\ 
 
 UNITED STATES COAST SURVEY. 
 
 DIRECTIONS 
 
 OBSERVATIONS OF TIDES. 
 
 FREWTEM* FOR VIEE USE OF TIME VEEt.EE ORSERVERS FROM 
 TEEE JfE^JTEJSCREJPr EJVSVREJCTEOJYS, 1852. 
 
 Gideon & Go ; Printers. 
 
 L 
 
r 
 
UNITED STATES COAST SUKVEY. 
 
 DIRECTIONS 
 
 OBSERVATIONS OF TIDES. 
 
 PRIJYTEB FOR TBE USE OF VBF TJB^JL OBSERVERS FRO. 11 
 TBE JfT^JTUSCRIPT EJTSTRWJCVIOJYS, 1852. 
 
 Gideon & Co. ; Printers. 
 
 i 
 
 ' > 
 
 \V- \ 
 

 <P 
 

 
 ^ 
 
 INSTRUCTIONS 
 
 FOR OBSERVERS OF TIDES EMPLOYED BY THE U. S. COAST SURVEY. 
 
 H 
 
 The tidal stations are either permanent (for the year) 
 or temporary. The object of the permanent stations is 
 to determine with precision the establishment, rise and fall, 
 and duration of tides, and the effect upon them of atmos- 
 pheric and other circumstances, so as to form a tide table, 
 or one for the prediction of tides at the place. The com* 
 parison of the precise results thus obtained at suitable 
 points of the coast, will give the progress of the tide wave. 
 (Genl. Hydrog. Instruc, 1845, Par. 19.) 
 
 There are certain tidal stations established for the spe- 
 cial purpose of determining the progress of the tide wave 
 by observations of a short period, where all the precautions 
 should be taken as at a permanent station. 
 
 INSTRUCTIONS FOR OBSERVERS AT PERMANENT TIDAL STATIONS OB- 
 SERVING HIGH AND LOW WATER ONLY. 
 
 Tide Gauge. 
 
 1. The gauge should, when practicable, be of the form 
 called the box gauge, having a copper float, a wooden rod 
 graduated to feet and tenths, and reading by a vernier, or 
 by estimation, to hundredths 5 graduated so that greater 
 readings correspond to rise of tide and smaller to fall 
 The holes admitting the water to the box should be nu~ 
 merous enough and large enough to admit it freely, but not 
 to permit oscillation. A slide should be provided which 
 will enable the observer to cover a greater or less number 
 of these holes, so as to vary the facility of access of the 
 water to the gauge under different circumstances of wind, 
 &c. 
 
In establishing the gauge, care should be taken that, at 
 the lowest water to be observed, there is still at least six 
 inches under the float, and that the highest range possible 
 is attainable by the marks on the staff. 
 
 If the situation will not allow a box gauge, a simple 
 staff, graduated upwards, and reading to feet and tenths, 
 may be firmly planted, and observed directly or through a 
 small telescope from a distance of twenty or thirty feet. 
 
 A permanent mark, corresponding to the zero of the 
 tide staff, should be made near the gauge ; a copper nail, 
 the centre of the head corresponding to the zero, and 
 surrounded by a circle of nails of the same material, or a 
 line cut into a stone ; or the zero should be referred by 
 the difference of level to some permanent mark, as the 
 plinth of a light-house, or the corner-stone of some adja- 
 cent building. 
 
 The highest or lowest tide known in the vicinity, its 
 date and circumstances, should be recorded. 
 
 Observations, 
 
 2. High and low water must be observed both night and 
 day; the time, and the height, and the interval of slack- 
 water being carefully ascertained. 
 
 About twenty minutes before the time of high water, 
 and ten minutes after, the observations must be made 
 every two minutes, and must be recorded, whether the 
 reading is the same or varies. 
 
 The time should be mean solar time. The watch used 
 should be corrected daily, when the sun shines, by a mark 
 furnished by the chief of the hydrograpbic party estab- 
 lishing the tidal station, or to be otherwise procured, when 
 this resource fails, for the sun's meridian passage, and an 
 almanac, or extract from one, showing the equation of 
 
time to be applied, and whether additive or subtractive, to 
 convert apparent solar time into mean solar or clock time, 
 
 3. Besides the observations of rise and fall of tide, me- 
 teorological observations are required, including those of 
 the barometer, thermometer, hygrometer, and of the di- 
 rection and force of the wind, for which special instruc- 
 tions will be given. 
 
 Records. 
 
 4. The observer will be furnished with printed forms for 
 his records. The original to be kept in a bound volume, 
 the duplicate on loose sheets. He should, from day to 
 day, make a copy of his observations on the loose sheets, 
 and at the end of each month send them to the Coast 
 Survey office, and on the acknowledgment of their re- 
 ceipt send the original. 
 
 The packages sent are to be placed in a cover addressed 
 " Coast Survey Office, Washington, D. C ,-" over which a 
 second cover is to be placed addressed " Hon. Thomas 
 Corwin, Secretary of the Treasury, Washington, D. C; " 
 on each cover, in the upper right hand corner, is to be 
 written "Official Business." 
 
 The original and duplicate must be commenced by a 
 description of the gauge, stating its form, dimensions, 
 graduations, &c, the points to which its zero is referred, 
 a sketch of the locality where it is placed, and notes of 
 the general character of the place in reference to sur- 
 rounding objects. Especially the influence which the 
 position is likely to have in retarding the tide wave, or 
 preventing or augmenting its rise, or the effect of winds in 
 raising or depressing the water, and on the time of high 
 or low water. 
 
 The mark of reference must be carefully described. The 
 date of observations and names of the tidal observers must 
 
appear on the face of the record, and all blanks in the 
 forms be filled up. 
 
 The time of high and low water should have written 
 opposite to them in the column of remarks, "H." and "L." 
 water, and the time of slack water, (when there is no rise 
 or fall,) should be noted below. 
 
 Remarks. 
 
 5. Observers cannot be too careful to note the facts pre- 
 cisely as they occur, without regard to what may seem to 
 them to be the regular succession of heights and of times. 
 What appear to be irregularities are frequently most im- 
 portant phenomena. Any attempt to force the observa- 
 tions, will, when detected by a comparison of results or 
 otherwise, deprive the observer at once of employment. 
 
 If an observation is accidentally omitted, its place should 
 be left blank, and allowances will be made for such omis- 
 sions, unless frequent, or the result of carelessness. 
 
 Negligence should be reported at once to the officer in 
 charge of the station, or, when there is no one in special 
 charge, to the office. 
 
 The observers will remark, that the observations of the 
 night tides are a& essential as those of the day tides. 
 
 Meteorological observations. 
 
 6. The directions of the wind are to be observed to the 
 nearest points ; an easy moving vane being mounted for 
 that purpose on a tall pole, with a small flag as a check, 
 and a circle divided below. 
 
 The circle is to be made on a stick of timber fixed firmly 
 in the ground, and divided like the mariner's compass into 
 points and half points. 
 
 In the centre of the circle the pole with the flag is to 
 be placed. The observer, in making the observations, has 
 
7 
 
 only to notice the direction in which the vane is blown, 
 and, referring to the stationary compass, notice the direc- 
 tion of the wind. 
 
 The force of the wind is to be recorded according to the 
 scale, as follows: 
 
 Table of force of winds. 
 
 Velocity in miles per hour. 
 
 0. Calm - - - . o 
 
 1. Light air ------ 1 
 
 2. Light breeze ----- 4 
 
 3. Moderate breeze - 13 
 
 4. Fresh breeze ----- 23 
 
 5. Strong breeze ----- 32 
 
 6. Fresh gale 40 
 
 7. Strong gale 50 
 
 8. Whole gale 60 
 
 9. Storm 80 
 
 10. Hurricane 100 
 
 7. The mean time to be given by a mark to be placed as 
 above stated ; by which, and an almanac to be furnished 
 to the observers for the equation of time, they will regu- 
 late their watches. 
 
 8. The height of the barometer, and temperature by 
 attached thermometer, to be noted when the tides are 
 observed. 
 
 The temperature, by a thermometer in the air, and 
 carefully screened from reflected or radiated heat, to be 
 observed at the same time. 
 
 The temperature of the wet bulb thermometer to be 
 also observed. 
 
 Description and use of the " Alexander barometer" 
 
 9. The following is a description of the mode of mount- 
 ing and using the Alexander barometer, which has been 
 furnished to most of the tidal stations : 
 
This barometer, as made by Mr. James Green, of New 
 York, consists essentially of an iron cup or cistern I, sup- 
 ported by a metal bracket E, (see the annexed sketch,) and 
 containing mercury, in which is immersed the barometer 
 tube, B, sustained at the upper end by a metal clamp and 
 hook, o and /, and attached to the wall by means of the 
 metal bracket F ; a scale of inches and tenths is marked 
 upon the tube, on which slides a vernier, L, reading to 
 hundredths, the zero of the graduation being a line marked 
 upon the tube near its lower extremity. A small iron 
 socket, g-, having in it a single hole, which can be closed 
 by the screw, c, is firmly attached to the lower end of the 
 tube. An ivory float, K, is made to fit loosely around the 
 barometer tube, and allowed to rest upon the surface, a &, 
 of the mercury in the cistern, it being easier for the eye 
 to note the coincidence of an ivory edge than a mercurial 
 surface with the zero line. The nut, G, serves to raise or 
 lower the tube at pleasure. 
 
 When the barometer is to be set up, the tube filled with 
 mercury, and closed at the lower extremity by the screw, 
 c, is taken from the case carefully inverted, and, with the 
 lower end immersed in the cup or cistern of mercury, is 
 held in that position until the ivory float and moveable 
 vernier can be slipped round it, and the metal hook clamped 
 to its upper extremity ; the finger is then carefully inserted 
 beneath the mercurial surface, and the screw taken out — 
 slowly, so that the mercury in the tube may fall gradually 
 to its proper height. The vernier is then adjusted to the 
 scale, and the instrument is ready for use. 
 
 In taking down the barometer, the ivory float, the ver- 
 nier, and the metallic hook by which the tube is suspen- 
 ded, are first detached from it. The tube is then carefully 
 inclined, its lower extremity being kept immersed in the 
 mercury until the fluid rises to the top and completely fills 
 
9 
 
 the tube. The small screw is then inserted in the orifice, 
 and the barometer being removed from the cistern is in- 
 verted and placed in its leathern case, which is so contrived 
 that the tube hangs in it suspended from its metallic socket. 
 The diameter of the tube is about one-sixth of an inch. 
 
 The reading of the barometer is noted by first making 
 the edge of the ivory float coincide with the zero mark on 
 the tube. This is effected by means of a screw, H, inserted 
 underneath the iron cistern, and working in a metal support, 
 so that the cup of mercury, and with it the float, can be 
 elevated or depressed at pleasure. Supposing this done, 
 we proceed to observe the height of the summit of the 
 column. Take hold of the tube with the left hand so that 
 it may retain as closely as possible its vertical position, and 
 tap slightly upon it near the top of the column ; this breaks 
 any adherence which may have taken place between the 
 mercury and the glass. Then move the slide, M, which 
 carries the vernier, until the plane, passing through its zero, 
 is tangent to the top of the convex surface of the mercurial 
 column. It is well to have a screen of white paper placed 
 behind the barometer to assist the eye in determining when 
 the meniscus thus formed is perfect, that is, when the 
 summit of the column and the edge of the slide just touch 
 each other, leaving no line of light between. Before read- 
 ing it, it is better to allow the barometer to remain at rest 
 a few moments, and then note whether the zero line still 
 remains tangent to the convex surface, and whether the 
 edge of the float still coincides with the zero of the scale. 
 If these adjustments still continue exact, the inches and 
 tenths are then read off from the scale, and the hundredths 
 from the vernier. 
 
 10. A small thermometer should be attached to the 
 tube, and the bulb of another be allowed to dip in the cup 
 of mercury, by which the temperatures of the tube and 
 of the mercury may be noted. 
 2 
 
10 
 
 For the mode of placing the thermometer to give the 
 temperature of the air, of reading and verifying, see the 
 directions for meteorological observations by the Smith- 
 sonian Institution .* 
 
 11. The same directions are to be followed in regard 
 to placing, observing and verifying, the wet bulb ther- 
 mometer, the rain and snow gauges, the character of the 
 sky and of the clouds. The direction and force of the 
 wind, however, will be observed and recorded as already 
 stated in these instructions. 
 
 12. Those observers to whom the Smithsonian barom- 
 eters have been furnished should follow the same instruc- 
 tions for using that instrument. 
 
 INSTRUCTIONS FOR OBSERVERS AT PERMANENT TIDAL STATIONS 
 OBSERVING HOURLY. 
 
 13. To the requirements in the foregoing instructions 
 are added observations hourly during the day and night. 
 
 When the rise and fall of the tide is small, as in the 
 Gulf of Mexico, the observations near the times of high 
 and low water need not be taken more frequently than 
 every fifteen minutes ; and where the time of occurrence 
 of high and low water is irregular, so that there are 
 sometimes two high and two low waters, and at other 
 times there is only one high and one low water, in the 
 twenty-four hours, regular half hourly observations are to 
 be preferred to any attempt to determine more minutely 
 the time of high and low water. 
 
 When hourly tidal observations are made, the barometer 
 and attached thermometer, the detached thermometer, 
 with dry and wet bulb, and other meteorological instru- 
 ments, will be observed at the times and according to the 
 
 * Directions for meteorological observations, intended for the first class of observers, 1850. 
 
11 
 
 rules given in the instructions of the Smithsonian Insti- 
 tution in the chapter entitled " Time of observations." 
 The direction and force of the wind, and general character 
 of the weather, will be recorded every hour. The scale 
 to be used for the force of wind is that given in these 
 instructions. 
 
 THE END. 
 
THE ALEXANDER hAKOMKTKK 
 
 D 
 
 V„ - X 
 
AI.KXAXDKH KAHOMKTKK 
 
 £■ 
 
 I- J 
 
 • Mi. ;pn /. 
 
i 
 
\ 
 
 LIBRARY OF CONGRESS 
 
 a' 029 ivTzsF™