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 By James B. Francis, C. E. 
 
 From tlie Joujrual of tite Fraukllu Institute. 
 
 Articles have appeared in the May and August numbers of tliis 
 Journal relating to the obstruction of the strainer of the inlet-pipe 
 of the Detroit Water-works by ice in 25 feet depth of water. As sug- 
 gested by Professor Henry, this is undoubtedly an example of ground 
 or anchor-ice. Perhaps a brief account of some of the circumstances 
 attending this curious phenomenon, in another place, may aid in elu- 
 cidating the Detroit example. 
 
 The manufacturing establishments at Lowell are driven by water- 
 power derived from a fall of about 34 feet at Pawtucket Falls in the 
 Merrimack River. The dam at the head of the falls sets back the water 
 about eighteen miles to the foot of the next fall above. Usually, be- 
 fore the middle of December, the entire reach of eighteen miles is 
 frozen over. In ordinary stages of the river, nearly its whole flow is 
 diverted into the canals by the dam, and is used by the manufacturing 
 establishments. The current in most of these canals is too rapid to 
 allow them to be frozen over. At times, the operation of the mills is 
 seriously interrupted by anchor-ice, the formation of which is evidently 
 connected with the open water, as at the mills which are supplied with 
 water from the river through canals which are frozen over, there is 
 no anchor-ice, while at others, supplied from the same source, through 
 canals not frozen over, great trouble is experienced. In fact, it is 
 uniformly observed that anchor-ice is found only at or below open 
 water. The water is usually kept flowing through the canals during 
 the night, when the mills are not in operation, passing over dams or 
 weirs constructed for the purpose. During some part of most winter 
 nights anchor-ice forms, and, in severe weather, men are employed 
 through the night, in cutting it away from the tops of the dams, in 
 order to prevent overflows. 
 
 Anchor-ice is an aggregation of small crystals or needles of ice, 
 forming in the water a spongy mass, easily penetrated with any hard 
 substance. It is frequently found adhering in large quantities to the 
 bottom and sides of the water-courses, both open and covered. In 
 clear weather, as the sun approaches the meridian, masses of anchor- 
 ice often rise from the bottom of the open channels and float off", some- 
 times with earth and small stones adhering. It is produced in the 
 greatest abundance in cold, clear, windy nights. It unquestionably 
 originates at the surface of the water, the necessary conditions being, 
 that the water should be at the freezing temperature, the air below 
 that point and the surface of the water agitated, either by a current 
 
or by the wind. In its first stage, the ice is in small detached noedles 
 or crystals ; if there is little or no current, this ice accumulates at the 
 surface and finally consolidates into a sheet ; if the current is too st.-ong 
 to permit this, portions of it accumulate in spongy masses, and iloat 
 along at or below the surface, their specific gravity differing but little 
 from that of the water. In a current of water there is a constant inter- 
 mixture of the water at diflferent depths, producing a uniform tempe- 
 rature at all depths, and tending to distribute uniformly foreign mat- 
 ters held in suspension. This takes place even in the most uniforra 
 and regular channels. Natural water-courses are almost always 
 irregular in form; the more irregular the more rapid will be the inter- 
 mixture. 
 
 The anchor-ice being formed in small crystals at the surface.^ by 
 means of this intermixture, much of that which does not aggregate in 
 masses, is carried down from the surface, and is distributed thrcugh- 
 out the whole depth of the stream, much in the same manner as 
 earthy matters are carried along in suspension by currents. These 
 crystals have a strong tendency to adhere to each other or to any 
 other solid bodies they may come in contact with. The adherence can 
 only take place by freezing, that is, by a new formation of ice, and 
 here lies the mystery of anchor-ice. How can water become ice with- 
 out a loss of heat ? 
 
 Anchor-ice is observed to adhere to surfaces of stone or wood, over 
 which the water is running with considerable velocity, in some cases 
 exceeding 20 feet per second, growing up under this rapid current at 
 the rate 9f an inch or more per hour. It is clearly not dependent upon 
 radiation in the manner Dr. Wells has shown dew to be formed, for 
 we find the piers of bridges and the interior surfaces of subterranean 
 water-courses, where there can be no loss of heat by terrestrial radia- 
 tion, covered with anchor-ice. 
 
 Faraday has shown, ( G-laciers of the Alps-, by J. Tyndall, page 851,) 
 "that when two pieces of ice, with moistened surfaces, were placed in 
 contact, they became cemented together by the freezing of the film of 
 water between them, while, when the ice was below 82° Fahr., and 
 therefore dry, no effect of the kind could be produced. The freezing 
 was also found to take place under water ; and, indeed, it occurs even 
 when the water in which the ice is plunged is as hot as the hand can 
 bear." It has been suggested that the union in these experiments is 
 accomplished by a process analogous to the welding of metals. It 
 might account for the adherence of the crystals of anchor-ice to each 
 other, but not to other substances. 
 
 The following explanation of the process has been suggested. The 
 formation of ice is a kind of crystallization, requiring time for its 
 development. Anchor-ice commences to form at the surface of water, 
 agitated either by a current or by the wind. The water being at the 
 temperature of 32° Fahr., and the air at a lower temperature, heat 
 passes from the water to the air, equivalent to the formation of a cer- 
 tain amount of ice ; the water being agitated and the ice in minute 
 crystals, the latter become mixed witti the water before all the ice due^ 
 
t.t the loss of heat is formed ; and, although the crystals are removed 
 trmi further loss of heat, they will continue to enlarge, until an equi- 
 librium is attained. The amount of ice formed after the crystals leave 
 tiie surface may be very small, but still be sufficient to cause them to 
 avlhere, when, by means of the current, they are brought in contact 
 with each other, or with any other solid at the freezing temperature. 
 
 If this explanation is correct, the freezing process must continue 
 for a considerable interval of time after the crystals leave the surface, 
 as we have found, on drawing the water out of a subterranean water- 
 course, the whole interior surface of the channel coated with anchor- 
 ice, with great uniformity and symmetry, and several inches in thick- 
 ness. This ice must have formed before it entered the subterranean 
 channel and subsequently adhered. 
 
 Great inconvenience from anchor-ice is occasionally experienced at 
 Lowell. It has been stated, that the dam there sets back the water 
 about eighteen miles, forming a quiet reach of water usually frozen 
 over early in the winter, which prevents the formation of anchor-ice 
 on its surface. This ice is sometimes carried out, in the depth of win- 
 ter, by a freshet. In December, 1863, this happened. On the 13th 
 and 14th there were heavy rains, causing a rise in the river, which 
 carried out the ice and discolored the water with earthy matter. In 
 the night between the 15th and 16th, the wind was high from the 
 north-west, anchor ice making freely with the thermometer at 30°. 
 At 6 A.M., on the 16th, the wind was fresh and the thermometer at 
 26°, the anchor-ice forming very freely. The water-wheel for moving 
 the sluice-gates of the Northern Canal could not be started, on ac- 
 count of anchor-ice having choked up the orifice through which the 
 water is drawn. No anchor-ice is ever found at this wheel when 
 the river is frozen over. The unusual amount of anchor-ice at this 
 time, forming at such a high temperature, was attributed to the high 
 wind and rapid current in the river, and the great extent of open water 
 surface above the dams on which anchor-ice could form. Part of the 
 anchor-ice thus formed passed into the canals, where it adhered to the 
 sides of the water-courses and orifices, greatly obstructing the flow of 
 the water. In such a case, the frozen surface of some of the canals 
 is very little protection, as the anchor-ice made in the river becomes 
 so thoroughly mixed with the water that it forms part of the stream 
 at all depths, entering the canals with the water and flowing under the 
 surface-ice. Strainers, used to prevent other substances than water 
 from passing into orifices, are sometimes obstructed to such an extent 
 that little or no water can pass through them. 
 
 The circumstances attendinsr the formation of ice on the strainer of 
 the Detroit Water-works do not appear to differ in any essential par- 
 ticular from that attending the formation of anchor-ice at Lowell. 
 The depth of 25 feet, at which ice was formed at Detroit, is greater 
 than it is found at Lowell, where none of the canals exceed 20 feet 
 in depth, and are generally 10 feet or less. If, however, they were 25 
 feet deep, we should expect anchor-ice to gather at the bottom of them, 
 pretty much as it does now, if the surface remained unfrozen. 
 
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