A RESUME OF THE VARIOUS METHODS EMPLOYED FOR THE DETERMINATION OF e/m FOR THE ELECTRON BY CHARNJIT SINGH B. S., in Electrical Engineering, University of Illinois, 1917 THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN PHYSICS IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS 1921 ... ■ ' ■ w \ 3 £\ %k G UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL May_az 19121 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY. ChARNJ IT SINGH ENTITLED A,MStIMiL P F_..m EM PL OYED F O R ini?, DETERMINATION OF e/m FOR TiiE ELECTRON BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR Recommendation concurred in* Committee on Final Examination* *Required for doctor’s degree but not for master’s A 4 Digitized by the Internet Archive in 2015 https://archive.org/details/resumeofvariousmOOsing TABLE OF CONTENTS I HISTORICAL SKETCH 1 II DETERMINATION OF e/m General Theory 3 Wiechert Method 6 Kaufman Method. 9 Thomson Methods (a) First Method 13 (b) Second Method 18 III DETERMINATION OF e/m FOR PARTICLES SET FREE BY ULTRA- VIOLET LIGHT AND FOR THE NEGATIVELY CHARGED PARTICLES EMITTED BY INCANDESCENT SOLIDS 23 (a) Lenard's Method (b) Sir J.J. Thomson's Method 25 IV M. AND MADAME CURIE'S INVESTIGATIONS CONCERNING RADIO- ACTIVE SUBSTANCES V SUMMARY OF RESULTS VI CONCLUSION 33 $ I. HISTORICAL SKETCH The word, "electron" was first suggested in 1891 by Dr. G. Johnson Stoney as a name for the natural unit of electricity: namely, that quantity of electricity wnicn must pass through a solution in order to liberate at one of the electrodes one atom of hydrogen cr one atom of any equivalent substance. The word "electron" was intro- duced to denote simply a definite elementary quantity of electricity without any reference to the mass or inertia which may be associated with it. Professor Stoney implies tnat every atom must contain at least two electrons; one positive and one negative, because other- wise, it would be impossible that the atom as a whole be electrically neut ral. It is obvious that a word is needed which denotes merely the elementary unit of electricity and has no implications as to where that unit is found, to wnat it is attached, with wnat inertia it is associated, or whether it is positive or negative in sign; ana it is also apparent that the word "electron" is the logical one to associ- ate with this conception. J.J. Thomson’s word corpuscle is a very appropriate one to denote tne very minute inertia with which the nega tive electron is found associated in cathode rays. With the discovery, due to use of the new agency, X rays, the atom as an ultimate indivisible rhing was gone, and tne era of the constituency of the atom began. And witn the astonishing rapid- ity during the past twenty five years the properties of the sub- atomic world has been revealed. Physicists began at once to ask diligently and to find at least partial answers to questions like these: 1. What are the masses of the constituents of the atoms torn ■ ' . ■ 2 asunder by x rays ana similar agencies? 2. What are tne values of the charges carried by tnese con- st ituents? 3. How many of these constituents are there? 4. How large are they, i.e., what volume do they occupy? 5. What are their relations to the emission and absorption of light and heat waves, i.e., of electromagnetic radiation? 6. Do all atoms possess similar constituents? In other words, is there a premordial sub-atom out of which atoms are made? The partial answer to the first of these questions came with the study of the electrical behavior of rarefied gases in so- called vacuum tubes. Sir J.J. Thomson and Wiechert showed independ- ently in 1897 that the value of e/m for the negative ion in sucn ex- 7 hausted tubes is about 1.8 x 10 electromagnetic units, or, about 180C times the value of e//m for hydrogen ion in solution. Since the ap- proximate equality of ne, (n is the number of molecules per cu.cm.) in gases and solution meant that e was at least of the same order in both, the only possible conclusion was that the negative ion which appears in discharges in exhausted tubes has a mass, i.e., a» inertia only l/1800th of the mass of the lightest known atom, namely, the atom of hydrogen. Furthermore, these and other experiments have snown that e/m for the negative carrier is always the same wnatever be the na- ture of the residual gas in the discharge tube. This was an indi- cation of an affirmative answer to the sixth question above, an indi- cation which was strengthened by Zeeman's discovery in 1897 of the splitting by a negative field of a single spectral line into two or three lines, for this wnen worked out quantitatively, pointed to the • ■ . . . , . 3 existence witnin tne atom of a negatively cnarged particle which had approximately the same value of e/m. Attempts had been first made at a direct determination of _e by Townsend in 1897, and was followed by J.J. Thomson, H. A. Wilson, Bogeman and Millikan. The latrer ap- plied a number of methods: One of them being the method of obser- vation. His results are given below in the table. The table is taken from Millikan's book entitled "Tne Electron":- Serles Charge Value of e Weight assigned 1 3e 4.59 7 2 4e 4.56 7 3 2e 4,64 6 4 5e 4.83 4 5 2e 4.87 1 6 6e 4. 69 3 The study of e/m for positive ions in exhausted tubes tnough first carried out quantitatively by fien has been elaborately and most successfully dealt with by Sir J.J, Thomson. The results of the works of all observers up to date seem to show quite conclusively that e/m for a positive ion in gases is never larger than its value for the hydrogen ion in electrolysis, ana that it varies with differ- ent sorts of residual gases just as it is found to be in electrolysis II. DETERMINATION OF e/m General Theory .- Different methods have been used to deter- mine the ratio e/m for small particles, but most of the calculations depend on some experimental investigations of the effect of a mag- netic force on the motion of the particle. The simplest case is that of a particle moving in a vacuum in which the electric force is . -f 4 zero and. tne magnetic force H is perpendicular to tne direction of the motion. If v be the velocity of the particle, tne force hev act- ing on it is in a direction at rignt angles to the direction of tne motion ana to tne magnetic force, so tnat wnen H is constant tne par- ticle moves in a circle witn a constant velocity. Tne radius r of tne circle is obtained by equating tne centrifugal force to tne force Hev along tne normal to the trajectory, nence: mv 3 /r = Hev or e/m = v 3 /rHv = v/rH. In a discharge tube containing a gas at a very low pressure tne electric force in the neighbornood of the cathode is large, so tnat tne particles set free from the catnode acquire a high velocity and may penetrate considerable distances without mucn loss of energy by collision with molecules. If tne electrodes are fixed at one end of tne tube, the rays move witn a velocity wmcn is approximately constant for tne remainder of their path, and tne curvature 1/r of their trajectory produced by a magnetic force may easily be found, so tnat one relation between tne two quantities e/m and v is tnus ob- tained. If in addition tne velocity v is known, or some otner rela- tion connecting e/m and v, tne values of botn of tnese quantities may be obtained. In 1890 scnuster read a paper before the Royal Society in which he mentioned tnat an upper limit and a lower limit for tne ratio e/m could be establisned. He mentioned that particles are projected from tne catnode. The observed effect of the magnet on tnem is exactly what it should be under the circumstances. The patn of tne particles can be traced by means of tne luminosity produced by tne molecular impacts. If . . . *- . . 5 the trajectory is originally straight, it bends under tne influence of a magnet. The curvature of the rays depends on two unknown quantities, the velocity of tne particles and the quantity of elec- tricity tney carry. If tne particles carrying a cnarge are moving with velocity at right angles to tne lines of force, tne radius of curvature r is determined by tne equation mv 2 /r = Hve or e/m = v/Hr, (1) where m is the mass of the particle, ana H the magnetic force. If the particles originally at rest start from the cathode at which the potential is taken as zero, and arrive without loss of energy, at a place where the potential is E, we should have another equation, namely 2Ee = mv 2 , (2) Eliminating v, we find e/m = 2E/H 2 r 2 . (3) A lower limit, he mentioned, can be calculated as follows: As long as the effect of the magnet on the particles projected from the cathode shows any directional preponder ence, we may take it that the velocities of the particles must be greater than the mean velo- city in their normal state. For it is clear that, if distribution of velocities was symmetrical in all directions, the magnet would have equal and opposite effects on the charges which move in opposite directions; and if by mutual impact the velocity is reduced to its normal value, it will also have lost any directional inequality. We may obtain a lower limit lor e/m if in equation (1) we calculate e/m = v/Hr (4) • . ■ , 6 by putting for r tne smallest radius of curvature wnicn can witn cer- tainty be traced in tne glow, and for v the mean velocity of tne par- ticle, according to tne kinetic energy of gases. In an actual experiment by Schuster, H was 200 gausses; r diminished with increasing distance from the cathode. The greatest value which could with certainty be measured was about 1 cm. E was 225 volts at the same place. Taking these numbers we get for the upper limit e/m 11 x 10^ and the lower limit he got to be e/m >1Q 5 . This lower limit for e/m as Schuster found, were very near the observed values. Wiecnert Method .- wiechert, in January, 18S7, first showed that tne ratio e/m for a cathode-ray particle is between 4000 and 2000 times as great as the value of e/m corresponding to an atom of hydrogen, tne velocity of the cathode being in some cases about one- tentn of the velocity of light, he attributed tne large value of e/m to the smallness of the mass m and considered the charges e and E to be the same. Wiechert, working with rays in hydrogen at a very low press- ure, measured the curvature 1/r of tne trajectory produced by a known negative force H, and obtained the value of Hv for substitution in the formula e/m = v/Hr. The velocity v was determined by a direct method in wmch tne period of oscillation of a condenser, discharging through a cir- cuit of known s elf- inductance was used to estimate the short interval h g d a 9 f £ ^ Figure i . 7 of time required by the rays to traverse a given distance in tne dis- charge tube. This principle had previously been used by aes Condres who found tnat the cathode rays nad a velocity exceeding 2 x 10 8 centimeters per second. Guided by this result Wiechert designed an apparatus by means of which it was possible to compare the time in which the rays traversed a distance of about 20 centimeters with the period of T of a condenser, T being between 10 ° and 10 second. The arrangement of apparatus is shown by the illustration of tne dis- charge tube (Fig.l). In front of the cathode, K, and at a distance 25 centimeters from it, he placed a plate of glass, G, that fluoresced brightly under the action of the rays. Two metal screens, and Bg, were placed between the catnode and the glass plate. The screen, Bg, was 5 centimeters from the glass plate and had a slit in tne centre a few millimeters wide. The otner screen, B^, 7-1/2 centimeters from the cathode extended across tne lower part of the tube, ana its edge was parallel to the slit in Bg. The positive electrode, which is not shown in tne figure, was in tne form of a ring ana was placed between tne cathode ana screen B^. The discnarge was produced by the secondary circuit of a Tesla transformer, and the rays from the cen- ter of the cathode, passed over the edge of tne first screen and througn the slit in tne second. A narrow fluorescent strip, a few millimeters wide, marJced tne points on the surface of glass, (*, on which the rays impinged. When a magnet was placed in a suitable position near the cathode most of the rays bent down and fell on tne screen B]_, and only a slight fluorescence was seen on the glass plate. Tne two wires, abed , and efgn , formed part of tne circuit of the oscillatory discharge of a condenser, which was charged * 8 inductively by tne Tesla apparatus used to produce tne cathode rays. Thus, a current flowed tnrough tne wires abed and at tne same in- stant the high potential was established between tne electrodes. When the wire is brought close to the tube, as shown in tne figure, the magnetic force due to the current in be counteracts tne effect of tne magnet, when the cathode rays are emitted, so that some of the rays pass over tne edge of B^. An increase is thus produced in tne fluorescence at G, due to the rays wnicn between K and B^, wnen tne alternating current in tne condenser circuit is in a certain phase. The effect of tne current on the rays as they pass from tne slit in Bg to the glass plate is tnen observed by bringing tne wire ef gh near tne tube. Let t be tne time in which tne rays travel from B 1 1 the Period of oscillation of the condenser discharge; tner if T is large as compared with t_, the deflection produced by the cur- rent in f£ is in the same direction as the deflection produced by be I If tne period of tne condenser discharge is reduced until f/4 = t, the deflection produced between Bg and G becomes very small. Thus, by observing tne displacement of tne fluorescence of tne glass plate obtained by reducing the period, T, the time, t, may be estimated. It was thus faund tnat for rays for which the value of &£ was 150, the velocity v was about b x 10^ centimeters per second}. 7 and the value e/m about 3 x 10 , tne true value being possibly greater than these numbers. Weichert also considered tne possibility of determining e/m from measurement of tne potential difference, W, between tne elec- trodes. An upper limit of the velocity of tne electron in tne tube may be obtained on tne hypothesis that the rays start fram tne * A . . 9 negative electrode and move freely under the electric force. The maximum kinetic energy acquired by the cnarged particle is then, Biv 2 / 3 = eW, ana e/m is given by the equation e/m = v 2 /2W # 7 The upper limit of tne value of e/m tnus obtained was 4 x 10 . Subsequently, the arrangement of tne apparatus for measuring the velocity of tne rays was made; the most probable values of e/m were found to be between 17 17 4.b4 x 10 and 6 . 04 x 10 x in electrostatic units and 1.55 x 10 7 and 1.01 x 10 7 in electromagnetic units, Kaufman* s Met nod . - Kaufman performed a number of experiment i in 1897, on the determination of e/m for cathode rays. He introduced a method by wnich the deflection due to electric and magnetic force takes place simultaneously and can be measured witn great accuracy. His method depends on the simple principle that in a gas at suffi- ciently low pressures the kinetic energy acquired by the electrons in passing from tne catnode to the anode is eW, W being tne potential difference between tne electrodes. Under these conditions, tne value of e/m is given by the formula e/m = 2W/H 3 r 2 , r being the radius of curvature of tne trajectory in a transverse magnetic field H. This implies that tne loss of energy of the elec- trons due to collisions is very small, and tne investigations snow tnat any sucn effect must have been negligible. Kaufman made a number of experiments in which the gas was at different small press- ures, and the potential difference between the electrodes required to produce the discharges varied from bOOO to 4000 volts. The 10 velocity was liaole to be diminisned appreciably due to the collision between tne rays ana molecules, so if W aiminishes error in tne for- mulae would increase. But it was observed that tnere was no appre- ciable difference in the value of quantity W/H 2 r 2 for different pressures at which tne experiments were performea. So tnat if we tak i eW as tne kinetic energy tne error wouia not be serious. Tne apparatus that Kaufman usea is snown in Fig, 3. Tne glass tube, R, 11 centimeters long and 6.b centimeters wide, was closed witn a gas plate, G, tne eiectroaes K ana P being contained in tne tube T. Tne ca-cnoae K was raised to a nign potential Dy a Wims- nurst macnine, and tne potential difference W between the electrodes was measured by an electrostatic voltmeter. The case of tne volt- meter and the positive electrode P were connected to earth. A thin layer of cnalk, wmcn fluoresced under tne action of tne rays, was spread over the plate G, an electrode wmcn was a platinum wire naif a millimeter in diameter, cast a snaaow on tne fluorescent plate. The magnetic force n was establisned in tne space between P ana G oy tne current in tne solenoid S. The deflection of tne rays was meas- ured by tne displacement d of tne shadow of the wire, ana since d was small compared witn tne distance PG, tne radius of curvature r of tne trajectory was inversely proportional to d (2rd = a 2 approxi- mately, a, being tne distance PG) . Experiments made witn a copper electrode at K gave tne fol- lowing results: With air at different pressures,, .03 to .07 millimeters. The potential W required to produce the discharge varied from 10630 v ol 1 8 to 3260 volts, but the quantity W/Hr remained constant, the mean value being proportional to 393, 398, 406, in a series of 11 experiments in which the cathode was placed at various distances from the wire P. With coal-gas the mean value 401.5 was obtained in experi- ments in which W varied from 6410 to 11850 volts. In hydrogen and carbonic acid the quantity J %/ Hr was found to be proportional to 404 and 398, the potential difference W rang- ing from 4000 to 14000 volts. An aluminum cathode was also used with air in the tube, and the results were the same as those obtained with the copper elec- trodes. Thus, the value of e/m is independent of the pressure, the distance between the electrodes, and the nature of the gas. In order to obtain an exact value it was necessary to take into account the fact that the field is not absolutely uniform and to take accurate measurements of the force H along the line from P to G due to given current in the coil S. When the rays traverse a distance x in the transverse mag- netic field, the velocity v at right angles to the original direction of motion is: v — f* He/m dx. so that the small deflection d on a screen at a distance a from the origin is = e/mv f dx f Hdx J o J o = Je/ 2mW j d n j Hdx. Later, Kaufman made a complete investigation of the magnetic 13 7 field and found the value of e/m for cathode rays to be 1.77 x 10 . Simon, working with tne same apparatus as Kaufmann, with sorr i n improvements, found the value of e/m to be 1.8B5 x 10. Thomson's Methods .- Sir J.J. Thomson, in 1897, determined e/m by two different and independent methods; and his values are in general agreement with those obtained by Kaufmann and Wiechert. (a) First Method.- He considered a bundle of homogeneous cathode rays, m being the mass of each of the particles, _e the charge N the number of particles passing across any section of the beam in a given time; then £ the quantity of electricity carried by these particles is given by the equation: Ne = Q. When these rays strike against a solid body the temperature of the body is raised; the kinetic energy of the moving particles being con- verted into heat. If we suppose that all this energy is converted into heat, then, if we measure the increase in the temperature of a body of known thermal capacity caused by the impact of these rays, we can determine W, the kinetic energy of the particle, and if u is the velocity of the particles, l/2Nmv 2 = W. If r is the radius of curvature of the path of these rays in a uni- form magnetic field H, then mv/ e = Hr = I where I_ is written for Hr for the sake of brevity. From tnese equa- tions we get l/3v 2 m/e = W/Q v = 2W/QI m/e = I 2 Q/2W. therefore 13 If we know W and I, we can deduce the value of e/m. Thomson used tubes of three different types; the first one is represented in Fig. 3, except that the plates E and D were absent. Two coaxial plates are fastened to tne ends of the tube. The rays from tne cathode _C fall on the metal plug B, which is connected with the earth, and serves for the anode. A horizontal slit is cut in the plug B. The cathode rays pass througn this slit and then strike against the two co-axial cylinders at the end of the tube. Slits are cut in these cylinders, so that the cathode rays pass into tne in- side of the inner cylinder. The outer cylinder is connected with the earth. The inner cylinder which is insulated from the outer one, is connected with an electrometer, the deflection of which measures the quantity of electricity Q brought into tne inner cylinder by the rays A thermo-electric couple is placed benmd the slit in the inner cylin - der. This couple is made of very thin strips of iron and copper fastened to very fine iron wires. These wires passed through tne cylinders, being insulated from them, ana tnrough the glass to the outside of tne tube, wnere they were connected with a low resistance galvanometer. The deflection of which gave data for calculating the rise of temperature of the junction produced by tne impact against it by the cathode rays. The strips of iron and copper were large enough to insure tnat every catnode ray which entered the inner cylinder struck against the junction. In some of the tubes the strips of iron and copper were placed end to end, so that some of the rays struck against the iron and others against tne copper. in otn- ers the strip of one metal was placed in front of the other. No dif- ference, however, could be detected between tne results gotten with these two arrangements. The strips of iron and copper were weighed. 14 in one set or junction and the thermal capacity A was 5 x 10” ^ microfarad, ana in the other 3 x 10”* 5 . If we assume tnat tne catnoae rays wmcn strike against tne junctions give tneir energy up to it, tne deflection of tne galvanometer gives us W or l/2Wmv 2 . The value of _I, i.e.. Hr, wnere t is tne curvature of tne patn of tne rays m a magnetic field of strength H, was found as f ol 1 ows : The tube was fixed between two large circular coils placed parallel to eacn otner, and separated by a distance equal to tne ra- dius of eitner. These coils produced a uniform magnetic field, the strength of which is gotten by measuring with an ammeter the strength of the current passing them. The cathode rays are thus in a uniform field, so that their path is circular. Suppose that the rays when deflected by a magnet strike against the glass of the tube at E as shown in Fig. 4. Then, if x_ is the radius of circular path of the rays. 2r CE 5 AC + AC. Then if we measure CE and AC we nave the means of determining the radius of curvature of tne path of the rays. The determination of r. is rendered to some extent uncertain, in consequence of the pencil of rays spreading out under the action of the magnetic field sc that the phosphorescent patch at je is sev- eral millimeters long. Thus values of jc differing appreciably from each other will be gotten oy taking E at different points of this phosphorescent patch. Part of this paten was, however, generally considerably brighter than the rest. When this was the case, E was taken as the brightest point. When such a point of maximum bright- ness did not exist the middle of the patch was taken for E. The 15 uncertainty in tne value of r tnus introduced amounted sometimes to about 20 per cent. By tnis it is meant tnat if we take E first at one extremity of the patch and then at the other, we should get val- ues of r differing by this amount. The measurement of £, the quantity of electricity which ent- er® the inner cylinder, is complicated by cathoae rays, making the gas through wnicn they pass a conductor, so that though the insu- lation of the inner cylinder was perfect when the rays were off, it was not so when they were passing through tne space between the cylin - ders. This caused some of the charge communicated to the inner cylinder to leak away, so that the actual charge given to the cylin- der by the cathode rays was larger than that indicated by tne elec- trometer. To make tne error from this cause as small as possible, the inner cylinder was connected to the largest capacity available, 1.5 microfarads, and the rays were only kept on for a snort time, about one or two seconds, so that the alteration in potential of the inner cylinder was not large, ranging in the various experiments from about .5 to 5 volts, another reason why it is necessary to limit the duration of the rays to as short a time as possible, is to avoid the correction for the loss of heat from tne thermo-electric junction by conduction along tne wires. The rise in temperature of the junction by conduction was of the order 2°C. a series of experiments showed that with the same tube and the same gaseous pressure, £ and W were proportional to each other when the rays were not kept on too long. Tubes of this kind gave satisfactory results. The chief drawback being that sometimes in consequence of the charging of the glass walls of the tube, a secondary discharge starfed from the cylinder to the walls of tne tube, ana the cylinders were surrounded Fig. 5- 16 by a glow. When this glov; appeared, the readings were very irregular The glow could, nowever, be gotten rid of by pumping ana letting the tube rest for some time. The results gotten with this tube by Sir. J.J. Thomson are given in Table I. The second type of tube was like the one shown in Fig. 5. A double cylinaer with a thermo-electric junction like those used in the previous tube were placed in the line of fire of the rays. The inside of the bell jar was lined with copper gauge connected with the earth. This tube gave very satisfactory results. There never ap- peared any glow around the cylinders, and the readings were more con- cordant. The only drawback was that some of the connections had to be made with sealing wax, ana hence it was not possible to get the highest exhaustion with this tube so that tne range of pressure was less than that for tube wo. 1. The results gotten with this tube are given in Table II. The third type of tube used by Sir J.J. Thomson was similar to the first one except that the openings in the two cylinders were made very much smaller. In this tube the slits in the cylinders were replaced by small noles about 1.5 millimeters in diameter. In con- sequence of the smallness of the openings the magnitude of the ef- fect was very much reduced. In order to get measureable results, it was necessary to reduce the capacity of the conaenser in connection with the inner cylinder to .15 microfarad, ana to make tne galva- nometer exceedingly sensitive, as the rise in temperature of the thermo-electric junction was in these experiments only about .5°C on the average. Tne results obtained in this tube are given in Table III. It will be noticed that the value of m/e is greater. . , . 17 TABLE I Gas Value of W/Q I air 4.6X10 11 230 air l.BxlO 12 350 air S.lxlO 11 230 air 2.5xl0 12 400 air 5. 5X10 11 230 air 1 P l.oxicr 285 air l.OxlO 12 285 hydrogen 6. OxlO 12 205 hydrogen 2. lxlO 12 460 card Ohio acid 8.4X10 11 260 carbonic acid 1. 4?xl0 12 340 carbonic acid 3. OxlO 12 480 m/e e/m V .57xl0” 7 1. 75xl0 7 4. OxlO 9 . 34xl0” 7 2, 94xl0 7 1. OxlO 1 . 43x1 0” 7 2. 33xl0 7 5. 4x1 0 9 . 32x1 0” 7 3. 12x1 0 7 l.BxlO 1 ' . 48x10” 7 2. 08x1 0 7 4. 8xl0 9 . 40x10” 7 2. 5x1 0 7 7. OxlO 9 . 40x1 0” 7 2. 5xl0 7 7. OxlO 9 . 35xl0~ ? 2. 86xl0 7 6. OxlO 9 . 50xl0” 7 2. OxlO 7 9. 2x1 0 9 . 40x10” 7 2. 5x1 0 7 7. 5x10® . 40xl0” ? 2. 5xl0 7 8. 5xl0 9 . 39x10” 7 2.57xl0 7 1.3X10 1 17a TABLE II gas value of W/Q I m/ e e/m V air 3. 8xlO n 175 ,53xl0” 7 1. 89xl0 7 3.3x10^ air 4.4X10 11 195 . 47xl0” 7 2. 13xl0 7 4.1x10' air b.SxlO 11 181 . 47xlO" 7 3.13xl0 7 3.8x10' hydrogen 3. 8X10 11 175 . 53x10*" 7 1. 89xl0 7 3. 3x10’ air 3.5X10 11 160 .51xl0” 7 1. 96xl0 7 3.1x10' carbonic acid 3. OxlO 11 148 . 54xl0~ 7 1.85xl0 7 2. 5x10* air 1.8X10 11 151 . 63x1 0" 7 1. 59xl0 7 2. 3x1 0^ hydrogen 3. 8x1 0 11 175 . 53x10” 7 1. 89xl0 7 3. 3x10' hydrogen 4. 4X10 11 301 . 46xl0” 7 2. 18xl0 7 4.4x10' air 3.5xlO U 176 . 61xl0~ 7 1 . 64xl0 7 2.8xl0 ! air 4. 3X10 11 300 . 48xl0” 7 3.08xl0 7 4. 1x10' TABLE Ill gas air value of W/Q 2.5X10 11 I 330 m/ e 90xl0” 7 e/m l.llxlO 7 V 2. 4xl0 9 air 3.5X10 11 235 70xl0” 7 1.43xl0 7 5.3xl0 9 hydrogen 3. OxlO 11 350 1. OOxlO*" 7 1. OOxlO 7 3.5xl0 9 18 considerably, for tube No. 3 than for Tubes No.l and 2. In tube No. 3 the opening is a small nole ana in No.l and 2 in is a slit of much greater area. The values of m/e gotten from tube No.l and 2 are too small, in consequence of leakage from tne inner to the outer cylinder by tne gas being rendered a conductor by the passage of the cathode rays. It will also be noticed that the value of m/e is independent of tne nature of the gas. Thus, for the first tube the mean for tne air is .4 x 10 7 , for hydrogen, .42 x IQ 7 , and for carbonic acid gas . 4 x 10 7 . For the second tube the mean value of m/e for air is .52 x -7 -7 -7 10 , for hydrogen .50 x 10 , and for carbonic acid gas .54 x 10 . (b) Second Met nod of Sir J.J. Thomson.- This method is based upon the simultaneous deflection of cathode rays in an electro- static field and in a magnetic field. If the deflection experienced by tne rays when traversing a given lengtn under a uniform electric intensity, and the deflection of the rays when tney traverse a given distance under a uniform magnetic field, are measured, the values of e/m and v can be found in the following way: Let the space passed over by the rays under a uniform elec- tric intensity F be 1_, the time taken by the rays to traverse this space is 1/v, the velocity in tne direction of F is therefore Fe ^ 1 m * v so that 0, the angle through wmcn tne rays are deflected when they leave the electric field ana enter a region free from electric force is given by the equation _ Fe 1 . 0 “ m • v^ 19 If, instead of the electric intensity, the rays are acted on oy a magnetic force H at right angles to the rays, and extending across the distance .1, the velocity at right angles to tne original path of tne rays is ■ . y , so that , tne angle tnrough which tne rays are deflected wnen tney leave tne magnetic field, is given by tne equation 6 = He 1 . ' gi * v From tnese equations we get and _e _ F_ 1 . m “ 0 * H 2 ‘ 1 In tne actual experiment ft is adjusted so tnat 9 = . In tnis case tne equation becomes and e _ £0_ . m H 2 1 The apparatus used in tnis experiment is represented in Fig. 6. The electric field is produced by connecting tne two alumi- num plates to tne terminals of a battery of storage ceils. The phos- phorescent paten at tne end of tne tube is deflected ana tne deflec- tion measured by a scale pasted on tne end of tne tube. As it was necessary to darken tne room to see the pnospnorescent patQh, a needle coated witn luminous paint was placed so tnat by a screw it could be moved up ana down tne scale. This needle could be seen when the room was darkened, ana it was moved until it coincided witn tne pnospnorescent patch. Thus, wnen light was admitted the deflec- tion on the pnospnorescent patch could be measured. . 20 The magnetic field is produced by placing outside tne tube two coils wnose diameter is equal to the length of tne plates. The coils are so placed so tnat tney cover tne space occupied by tne plates, me distance between tne coils is equal to tne radius of eitner. The mean value of the magnetic force over tne lengtn is determined in tne following way: A narrow coil 0 whose lengtn is 1 , connected witn a bal- listic galvanometer, is placed between the coils. Tne plane of tne windings of jC is parallel to the planes of tne coils. The cross- section of tne coil is a rectangle 5 cm. by 1 cm . 4 With a given cur- rent sent tnrough the outer coils, the kick of tne galvanometer is observed when this current is reversed. The coil C: is then placed at the center of the two very large coils, so as to be in a field of uniform magnetic force. The current through the large coil is re- versed and the kick of the galvanometer is again observed. By com- paring both kicks, first one called^, and the second one /3 , tne mea value of the magnetic force over a lengtn 1 is gotten. This was found by Sir J. J. Thomson to be bQ x i wnere _i is tne current flowing through the coils. Thomson maue a series of experiments to see if tne electrostatic deflection was proportional to tne electric intens- ity between tne plates. This was found to oe tne case. The results obtained by Thomson are given in tne following L table, he adjusted tne current through tne coils so that tne electro- static deflection was tne same as the magnetic. . , . . . . 21 gas 0 H F 1 m/e e/m V air 8/110 5.5 1.5 x 10 10 5 1.5 xllO“ 7 .77 x 10 7 2.8 xlO* air 9.5/110 5.4 1.5 5 1.1 .91 2.8 air 15/110 b. b 1.5 5 1.2 . 85 2, 5 hyarogen 9/110 b. 5 1.5 5 1.5 .67 2.5 carbonic acid 11/110 b. 9 1.5 5 1.5 • b? 2.2 air b/110 5.0 1.8 5 1.5 .77 2. 6 air 7/110 5.6 1.0 5 1.1 .91 2.8 The cathoae in the first five experiments was aluminum. In the last two experiments it was maae 01 platinum, in the last ex- periment Sir William Crookes' metnod of getting rid of the mercury- vapor by inserting tubes of pounded sulphur, sulphur iodide and cop- per filings between the bulb and the pump was adopted. In the calcu- lation of e/m and v, no allowance has been made for the magnetic force due to the coil in the region outside the plates. In this re- gion the magnetic force will be in the opposite direction to that be- tween the plates, and will tend to bend the cathode rays in the op- posite direction. Thus the effective value of H will be smaller than the value used in the equations so that the values of m/ e are larger and those of v much less than they would be if this correc- tion is applied. It will be seen from these determinations that the value of m/ e is independent of the nature of the gas, and that its value, 4 . 10 , is very large as compared with the value 10~ , which is the largest value of this quantity previously known, and which is the value for tne hydrogen ion in electrolysis. The same method as described above has been used a number 22 of times in the laboratory of physics at the University of Illinois, by Professor C.T. Knipp, The following results were obtained by three members of the graduating class of 1921, under his supervision. TABLE IV * Time PD I I s y z z 2 V e/m P 2.25 328.0 .183 .0335 1.25 1.75 6. 06 3.10 X 10 9 1.97xl0 7 . 00692 2.32 327.6 .180 .0324 1.275 1.80 3.24 3.01 X 10 9 1. 75xl0 7 .0078 2.39 327.2 .181 .0326 1.325 1.85 3.41 2.96 X 10 9 1. 75xl0 7 .0088 2.46 326.8 .175 .0306 1.42 1.90 3. 61 3.93 X 10 9 1. 82xl0 7 .00988 2.53 326.4 .182 .0331 1.50 2.00 4.00 2.80 X 10 9 1. 68xl0 7 .0106 3.00 326.0 .182 .0331 1.50 2.05 4.3 2.81 X 10 9 1. 69x10? .01116 3,07 325.6 .182 .0331 1.55 2.10 4.41 2.85 X 10 9 1.70xl0 V .0118 3.14 325.3 .183 .0335 1.56 2.15 4.61 2.89 X 10 9 1. 89xl0 7 . 01204 3.21 325.0 .183 .0335 1.60 2.20 4.84 3.88 X 10 9 1. 87xl0 7 .01268 3.28 324.6 .180 .0324 1.60 2.20 4.84 2.93 X 10 9 1.98xl0 7 .01312 3.35 324.3 .180 .0324 1.62 2.2 4.84 2.91 X 10 9 1. 90xl0 7 .01380 3.42 324.0 .176 .0310 1.725 2.2 4.84 2.78 X 10 9 *7 1.87x10 . 01428 3.49 323.5 .175 .0306 1.75 2.2 4.84 2.75 X 10 9 1. 80xl0 7 .01476 3.56 o23. 3 .181 .0326 1.80 2.2 4.84 2.58 X 10 9 1. 71xi0 7 . 01508 4.03 .175 .0306 1.85 2.15 4.61 2.54 X 10 9 1. 69xl0 7 . 01508 Another i set of data taken on a different date. 2.05 324. .187 .035 1.05 1.70 2.89 3.30 X 10 9 1. 74xl0 7 .0040 2.15 322.8 .1865.0347 1.18 1.80 3.24 2.95 X 10 9 1. 75xl0 7 .0067 2.25 321.6 .1865.0347 1.35 1.875 3.53 2.82 X 10 9 1, 66x10? .0085 2. 35 320. 4 . 1865 .0347 1.45 1.90 3.61 2.67 X 10 9 1.77xl0 7 .0100 2.45 319.2 .1865 .0347 1.55 2.00 4.00 2.62 X 10 9 1. 85xl0 7 .0112 2.55 317. .1865 JD347 1.60 2.05 4.20 3.51 X 10 9 1. 67xl0 7 .0116 23 While in the process of taking this data something went wrong and so after waiting a short time a new set of data was taken. The same is given below: Time PD I I 3 y z z 2 V e/m 9 3.25 317. .1865 .0347 .90 1.65 2. 72 3. 72xl0 9 1.91xl0 7 .0048 3.35 317. .1865 .0347 1.05 1.70 2.89 3. 29xl0 9 1.81xl0 7 .0050 3.45 317. .1865 .0347 1.10 1.75 3. 06 3.09X10 9 1. 77xl0 7 .0056 3.55 317. .1865 .0347 1.15 1.80 3.24 3.12x10 s 1. 75xl0 7 .0071 4.05 317. .1865 .0347 1.20 1.85 3.41 3.06xl0 9 1. 775xl0 7 .0081 III. DETERMINATION OF e/m FOR PARTICLES SET FREE BY ULTRA VIOLET LIGHT, AND FOR THE NEGATIVELY CHARGED PARTICLES EMITTED BY INCAN- DESCENT SOLIDS (a) Lenard's Method.- The earlier investigations of the negatively charged particles obtained by different methods in gases at low pressures show that the ratio e/m was probably exactly the same in all cases. Lenard in 1900, using a similar method to that of Xaufmann, determined the ratio of the charge to the mass of a particle set free by the action of the Ultra-violet light from a metal surface, and obtained the number 1.15 x 10 7 . His apparatus is shown in Fig. 7. A is an aluminum plate on which the ultra-violet light shines. This light comes from a spark between zinc electrodes and enters tne tube through tne quartz window, B. E is another metal electrode perforated in the middle and connected with the earth. It shields the right hand apparatus from tne electrostatic action of 34 the charged electrode, A. D and £ are electrodes which can be con- nected witn an electrometer. When A is cnarged up a stream of nega- tive electricity goes through the opening in E and, striking against the plate D, charges up the electrometer with negative electricity. If the electrometer be connected with £ instead of with D, it will net receive any charge. A charge, however, can be given to £ by de- flecting the stream of negative ions by means of a magnet until they strike against £. As we still further increase the magnetic field, the ions will be deflected by the field past £, and the charge com- municated to £ will fall off rapidly. The amount of negative elec- tricity received by the electrodes D and £ respectively, as the mag- netic force is increased, was in Lenard's experiments represented by the curves in Fig. 8. The ordinates are the charges received by the electrodes ana the aoscissae are the values of the magnetic force. The curve to the left is for the electrode D, that to the right for £. Since the negative ions are not exposed to any electric field in the part of the tube to the right of E3, their paths in this region under a constant negative field will be circles whose radii are equal to mv/eH. £ will receive the minimum charge when the circle with this radius passing through the middle of the hole in E, and having its tangent horizontal at this point, passes also through the middle of the electrode 0. The radius R of this circle is fixed by the relative positions of E and £. Hence, if we measure H when £ re- ceives its maximum charge, we have R = mv/eH. (1) Reiger found for the negative ions emitted by glass when exposed to ultra-violet light, values of e/m ranging from 9.6 x 10 to 1.2 x 10 7 . . . 25 (b) Sir J.J. Thomson’s Method..- Elster ana Geitel have shown that tne rate of escape of negative electrification at low pressure is much diminished by magnetic force if the lines of mag- at netic force are A right angles to the lines of electric force.. Let us consider wnat effect a magnetic force would have on the motion of a negatively electrified particle. Let the electric force be uniform and parallel to the axis of x, while the magnetic force is also uni- form ana parallel to tne axis of _z. Let tne pressure be so low that the mean free path of the particles is long as compared witn tne dis tance tney move while under observation, so that we may leave out of account the effect of collisions on the movements of the particles. If m is the mass of a particle, e. its charge, X tne elec- tric force, H tne magnetic force, the equations of motion are: Mfx _ y He dy and md s y _ tt dx . dt 2 " ne dt Eliminating x we have m 77^3 =lr 'Ue-iie The solution of tnese equations if x,y, dx/dt, dy/dt all vanish wnen t; is zero, is expressed by Xm eB 2 y = | -sxn^j X = Xm eH 2 cos Hte m 1 The equations show that the path of tne particles is a cy- cloid, the generating circle of which has a diameter equal to , eH 2 and rolls on the line X = 0. 26 Suppose now that we have a metal plate AB exposed to ultra violet light, placed, parallel to a large metal plate £D perforated so as to allow the lignt to pass tnrougn it and fall upon the plate AB . See Fig. 9. Then if CD is at a higher electric potential tnan AB, tne particles travel along the lines of electric force. Let us now suppose that a uniform magnetic force equal to h ana at right angles to the electric force acts on tne particles. These particles will now describe a cycloid ana will reacn a distance 3Xm eH 3 * Every particle whicn leaves AB will reacn £D provided CD stretcnes forward enougn to prevent tne particles passing hy on one side, now, tne distance parallel to jr tnrougn wnich tne particles have travelled wnen it is at tne greatest distance from AB is gjto . hence, if CD stretches beyond AB by this distance at least, all tne particles will be caugnt by CD ana tne magnetic field will produce no dimin- ution in the rate of leak between AB and _CD. If, on the other hand, tne distance between the plates is greater tnan then a particle starting from AB will turn back before it reaches CD. It will thus never reach it, ana tne rate at which CD acquires negative electri- fication will be diminished by the magnetic force, hence, if this view of the action of the magnetic field is correct, and if we begin with tne plates very near together, and gradually increase the dis- tance between them, we should expect that, at first with the plates quite close together, the rate at which CD received a negative charge would not be effected by the magnetic force, but as soon as the distance between the plates is equal to the magnetic force will greatly diminish tne rate at whicn CD receives a negative charge and will in fact reduce tne rate almost to zero if all tne negatively electrified particles came from the surface of AB. hence, if we . *"S . V * • , 27 measure the distance between the plates when the magnetic force first diminishes the rate at which CD receives a negative cnarge, we shall determine the value of and we can easily determine X and H, and eH 2 “ from tnem the value of e/m can be deduced. In the apparatus shown, AB is a carefully polished zinc plate about one centimeter in diameter; while CD is a grating com- posed of very fine wires crossing each other at right angles, the ends being soldered into a ring of' metal. The wires form network with a mesh about one millimeter square. This is placed parallel to AB on the quartz plate EF which is about four millimeters thick. The grating was very carefully insulated. The sy stern is enclosed in a glass tube which is connected with a mercury pump provided with a McLeod gauge. The ultra violet light is supplied from an arc about three millimeters long between zinc terminals. The induc- tion coil giving the arc is placed in a metal box, ana the light is placed through a window cut in the top of the box. Over this window the quartz base of the vessel is placed. A piece of wire gauze connected with the earth is placed between the quarts and the win- dow. The plate AB is carried by the handle L which passes through a sealing-wax stopper in the tube K, The magnet used is an electro- magnet of the horse shoe type. The magnetic force due to magnet is determined by observing the deflection of a ballistic galvanometer when an exploring coil, of approximately the same vertical dimen- sions as the distance between the plates AB and CD was withdrawn from between its poles. The coil is carefully placed so as to oc- cupy the same part of the magnetic field as that occupied by the space between AB and _CD when the magnet was used to affect the rate of leak of electricity between AB and CD . In this way the intensity of the magnetic iield between the poles of the magnet was determined 28 by Thomson for a series of values of the current through the magnet- izing coils of the electromagnet ranging between 1 ana 4.5 amperes, and a curve was drawn wnicn gave the magnetic force wnen tne magnet- izing current read, by an ammeter was known. The pressure of the gas in the tube containing the plate is reduced by tne mercury pump to 1/100 of a millimeter of mercury. The rate of leak of negative electricity to CD when AB was exposed to ultra-violet light is measured by an electrometer. The zinc plate is connected witn the negative pole of a battery of small storage cells. The positive pole of which is put to earth. One pair of the quadrants of the electrometer is kept permanently connected with the earth. The other pair is connected with the wire gauze CD. Initial- ly the two pairs of the quadrant are connected together; the connec- tion is then broken and the ultra-violet light is allowed to fall on the zinc plate. The negative charge received by the w[ire gauze in a given time is proportional to tne deflection of the electrometer in that time. By this method the following results were obtained by Thomson, When the difference of potential between the illuminated plate and the wire gauze was greater than a certain value depending upon the intensity of the magnetic force, ana the distance between AB and CD, no diminution in the deflection of the electrometer was produced by the magnetic field, in fact in some cases the deflection was just a little greater in the magnetic field. The negative ions travelling between the plates will disturb to some extent, the uniformity of the field between the plates. But if the intensity of the ultra-violet light is not too great, so that the rate of the leakage and the number of ions between the plates is not large, this want of uniformity will not be important. • . ‘ ' . . . ■ ■ . 29 Following is a specimen of Observations: Distance between the plates .29 centimeters Strength of the magnetic field 164 units Pressure P. D. between poles in volts 240 120 80 40 1/100 millimeter Deflection of electrometer in 50 seconds Magnet off Magnet on 180 160 160 150 190 165 140 75 These observations showed that the critical value of tne po- tential difference was about 80 volts. A series of observations was then made with potential difference increasing from 80 volts by two volts at a time, and it was found that 90 volts was the largest poten- tial difference at wmch any effect due to tne magnet could be de- tected. The results of a numoer of experiments are given in the fol- lowing table: d (in cm. ) H V (in absolute measurement) e/m .18 170 40 X 10 8 8. b x 1G 6 .19 170 50 X 10 8 5.8 x 10 6 . 20 181 46 X 00 o rH 7.1 x 10 6 .29 16? 84 X M O 00 7.1 x 10 6 .29 164 90 X O 00 7.6 x 10 6 . 50 160 86 X M O 00 7.4 x 10 6 .45 100 80 X M O 00 7.9 x 10 6 The mean ■ value for e/m is 7.3 x 10 6 . The value of e/m in case of tne convection of electricity under tne influence of ultra-violet lignt is of tne same order as in tne case of tne catnode rays, and is very different from tne value of e/m in tne case of hydrogen ions in ordinary electrolysis which is equal to 10^. The value, _e, is tne same, nence the mass must be dif- ferent and is of tne order of 1/1000 of nydrogen ion. Tnomson conducted experiments on tne determination of e/m for tne negative ion produced by an incandescent wire, nis metnod was tne same as descrioed above in case of ultra-violet lignt fall- ing on a plate. He found tne value of e/m to be 8.7 x 10^. Owen determined tne value of e/m for tne particles emitted by a glowing Nernst filament. He found tne value to be b.bb x 10^ and for tnose emitted by glowing lime Wennelt found tne value of e/m to be 1.4 x id 7 , IV. M. and MADAME CURIE’S INVESTIGATIONS CON- CERNING RADIOACTIVE SUBSTANCES M. and Madame Curie nad shown tnat tne radioactive suostanc^ radium emits negative ions. Becquerel determined the velocity of tnese ions and the value of e/m. His method was based upon tne de- flection of tne rays produced by an electrostatic and also by a mag- netic field. Tne pressure was atmospheric, ana the resistance of- fered to tne motion of tne ions by tne gas through which they pass was neglected. The case cannot be justified but for ions emitted by radium, as they are very much more penetrating than those tnat nave been hitherto considered, ana are able to travel as far tnrougn a gas at atmospheric pressure as others at low pressure. so tne value of v and e/m by this method would be right if the resistance of tne . - . . ' \ gas is neglected. V. SUMMARY OF RESULTS Careful investigations nave been made of tne ratio e/m and o tne results are in good agreement witn tne value 1.77 x 10' original- ly found by Kaufmann for catnode rays. The following are some of the recent determinations, _e being expressed in electromagnetic units. Slowly moving becquerel rays, oy magnetic ana electro- static deflection: Kaufman 1.884x 10 7 (1906) Buchner 1.766 x 10 7 (1909) Neumann 1.765 x 10 7 (1915) Cathode Rays: Bestelmeyer 1.73 x 10 7 (1907) Magnetic and eiec.defl, Malassez 1.769 x 10 7 (1911) n " " " between electrod Catnode Rays from glowing oxides, by magnetic deflection and potential difference oetween electrodes: Classen, 1.776 x 10 7 (1908) 7 Besrelmeyerl. 766 x 10 (1911) Photoelectric effect of magnetic deflection ana potential difference between tne electrodes: Allusti 1.756 x 10 7 and 1.766 x 10 7 (1913) Zeeman effect: Weiss and Colton 1.767 X 10 7 (1907) Stellenheimer 1. 791 X £V O i — i (1907) Omens s 1.771 X 10 7 (1909) (13 !i :w - . . 32 TABLE OF VALUES OF e/m e Source of Ions Observer Date Method of Value Determination of e/m v • 10 “ Cat node ray 8 J. J. Thomson 1897 g Magnetic and 7.7 x 10 electrostat ic deflection 2. 2-3. 6 Catnode rays J. J. Thomson 1897 Magnetic de- 1.17 xlO 7 flection and heating ef- fect 2* 4-3* 2 Catnode rays Kaufrnann 1897-8 Magnetic de- 1.86xl0 7 flection and potential dif- ference Cathode rays Simon 1899 7 Magnetic de- 1.865 x10 flection and potential dif- f er enc e Catnode rays Wie chert 1899 Magnetic de- 1.01 x 10 7 - f lection and 1.55 x 10 7 velocity of ions Cathode rays Seitz 1901 Magnetic and 6.45 x 10^ electrostat ic deflection 7* 03 Cathode rays Seitz 1902 Magnetic and 1.87 x 10 7 electrostatic deflection, heating ef- fect amd po- tential dif- ference 5. 7-7. 5 Cathode rays Starke 1903 Magnetic and. 1.84 x 10 7 electrostat ic deflection 3.8-12 Cathode rays Reiger 1905 Magnetic de- 1.32 x 10 7 flection and potential dif- ference Cathode rays Becker 1905 7 Magnetic de- 1.8 x 10 flection and retardation in electric field 10 . . 33 Source of Observer Dat e Metnod of Determination Value _g of e/m v • 10 Lenard rays Lenard 1898 Magnetic and electrostat ic deflection 6.39 x I0 6 Lenard rays Lenard 1898 Magnetic de- flection and retardation in electric field 6.8 x 10 6 3.4-10 Ultra-violet light J. J. Thomson ;899 Retardation of discharge by magnetic field 7r6 x 10 6 Ultra-violet light Lenard 1900 Magnetic de- flection and potential dif- ference 1.15* 10 7 Ultra-violet light Reiger 1905 Magnetic de- flection and potential dif- ference 9.6 x 10®- 1.3 x 10 7 Incandescent metals J. J. Thomson 1899 Retardation of discnarge by magnetic field 8.7 x 10 6 Incandescent oxides Owen 1904 Retardation of discharge by magnetic field 5.6 X 10® Incandescent oxiaes Wehnelt 1904 Magnetic de- flection and potential dif- ference 1.4 x ll 7 Radium Becquer el 1900 Magnetic and electrostatic deflection 10 7 approx- 3 x 10^ imately Radium Kaufmann 1901-3 Magnetic and electrostatic deflection 1.77 x 10 7 f or small velocities Polonium Ewers 1906 Magnetic and electrostatic deflection 1.7 x 10 7 « . . s . . . ■ . b4 VI. COwOLUSIOwS If compared, witn the charge on a univalent ion in a liquid electrolyte tne cnarge of tne negative ion obtained in nign vacua will be found to be tne same, Charge is not effected by pressure so tnere is a good reason to believe tnat tne cnarge is tne same a z all pressures. Tne large value of e/m Obtained for negative ion is due to tne smallness of m wnicn is less tnan tne mass of an atom of nydro- gen in tne proportion 1:1830. Kaufman investigated tne ratio e/m at nigner velocities approacning to tnat of light, and found tnat tne value of e/m dimin- 7 isnes from tne small velocity value to l.ol x 10 , wnen the velocity is 3.36 x lO 1 ^ and to .63 x 10^ when the velocity is 3.33 x 10^°. This fact has an important bearing on electromagnetic theory When an electric charge is in motion tnere is a certain amount of electromagnetic energy resident in the surrounding field, and the charge when accelerated exhibits the phenomena of inertia, even when supposed to devoid of ordinary mass. When the velocity approaches that of lignt the mass of an electron increases, while for slow speeds the electromagnetic mass is in the order of e 3 /a. j is the charge and a is the radius of the electron. For acceleration in the direction of motion tne charge be- haves as though it had a mass ^(longitudinal electromagnetic mass). While for acceleration at right angles to the direction of motion it appears to have a different mass transverse electromagnetic mass). Abraham and Lorentz in their theoretical investigations . . . . 35 have mentioned that the longitudinal mass is greater tnan the trans- verse mass. Abraham’s theory considers the electron as rigid, and Lorentz’s theory, for a special reason, considers it as contracting in the direction of the motion. Lorentz’s theory leads to the following formulae for m^ and in terms of the velocity v of the particle. m l = U-vVc 2 ) 0 ^ 2 = m Q / ( 1- v 2 / c 3 ) both masses being equal to m when v is small compared with £ the velo - city of light. This theory is justified since Kaufman’s original determin- ation of the transverse electromagnetic mass and the recent experi- ments of Bucheret with rays, and those of Hupka on fast cathode rays, are in agreement with it. All this supports the view that the mass of an electron is entirely electromagnetic. My most grateful acknowledgments are due to Professor A.P. Carman, Head of the Department, ana to Professor C.T. Knipp. The former afforded me all the facilities that were necessary to improve my knowledge, and generously helped me in every way possible in my work. I am mucn indebted to that knowledge and information which is acquired by one who has had the privilege of working in the Labora- tory of Physics of the University of Illinois under Professor C.T. Knipp who gave invaluable suggestions and also made a critical re- vision of the manuscript before it w'as typewritten in the final form. . . . . . . . , ■■ ' . . . BIBLIOGRAPHY Crowther, J.A.- "Ions, Electrons, ana Ionizing Radiac ion, iyi9. Millikan, R.A. - "The Electron", lyl7. Ramsay, Sir William - "Elements ana Electrons", 1912. Thomson, J.J.- "Conduction of Electricity tnrough Gases", 1906; Philosophical Magazine, Vol.44, p 293,(1897); Pmlosopnical Magazine, Vol.48, p 547, (1899). Townsend, J.S.- "Electricity in Gases", 1915. Schuster, A. - Proc. Royal Society of London, Vol.47, p 045 (1890/.