I C E. 



641 



the wur. 



of that of the arctic : The nearest approach made to 

 ' the South pole being 1130 miles, ami to the North 

 pole 510. Icebergs and floating ice of all forms abound 

 in the southern sea*, and present similar appearances 

 to those found in the northern. 



We shall now take notice of one circumstance in the 

 history of ice which is seldom particularly described, viz. 

 that it is found forming at the bottom of water, even on 

 large scale, while the surface remains liquid. This seems 

 contrary to what might be expected from the order 

 which takes place in the successive reduction of tempe- 

 rature in different parts of the same portion of water, as 

 well as from the comparative specific gravities of water 

 and ice. The facts are well ascertained, as occurring 

 in Germany, in Great Britain, and in North America. 

 In Germany two kinds of ice are described as formed in 

 that situation : one which is called tichl-tii, is the first 

 that is formed at the beginning of a severe frost, and 

 immediately rises to the surface in small grains, similar 

 to hail. The other, from retaining its situation longer, 

 is more commonly observed and better known. This 

 it called in Germany grand- fis. In Scotland, where it is 

 not uncommon, it it called grund-gmr, i. e. " ground- 

 grown.'' Men of science, not having attended to these 

 phenomena, have considered them, when accidentally 

 met with, as extraordinary. It has happened, when 

 they were in quest of something else, that they have 

 found at the bottom of a river a sandy man agglutina- 

 ted in a manner which they did not comprehend, till 

 they found that the cementing medium was ice. At 

 other times they have been struck with great surprise 

 on finding gravel, earth, or mud, mixed with ice on the 

 surface. But such phenomena are familiar to the fish- 

 ermen and boatmen on some of the northern rivers, par- 

 ticularly the Elbe. They sometimes find it difficult to 

 fix their ancbots, on account of the smoothness which 

 the ice imparts to the bottom. When taken up, the an. 

 chon arc sometimes coated with ice, and at other times 

 it forms on them in ucb quantities, as to raise them to 

 the surface by its buoyancy. Ice, instead of fish, is not 

 frequently brought up with the fish-hooks. The 

 sluice* and flood-gates are sometimes rendered immove- 

 able by the ice formed at the bottom. It often ac- 

 quires great thickness Itefore it rises, and then brings 

 up with it not only earth and gravel, but stone* of 

 Urge *ice. We are told, on credible authority, that in 

 the Elbe the tone* to which buoys had been fixed 

 a* mark* of the dangerous shallows, have been brought 

 to the surface by the grvitd en, and removed to a diffe- 

 rent part of the river. On the margins of lakes nume- 

 fragments of rack how MOB found on the 



subsiding of frort, which had been brought up In this 

 manner from the middle and floated to the edge. 

 species of bottom are more favourable to this process 

 than others : sand and gravel are more so than solid 

 rock. M. Bnran*. a Hanoverian, after consulting with 

 much care the best sources of information, learned that 

 m the northern sea*, trace* both of ikhl-tit and grund- 

 eit were found where the depth of the water was 108 

 tat. In the Bahk alone it was found at depth* still 

 greater. On* reason why these phenomena are seldom 

 observed i* that ship* return before the setting in of the 

 strong winter frosts. Mr Knight, in the I^ondon F/iHoio- 

 fktui Trm*Mtiuut for 1816, thus describes the pheno- 

 mena as they occurred under hi* own obsenratkm, and at 

 the same time delivers his opinion of their physical cause, 

 " I fir-t witneMed the existence of ice in the bottom of 

 the water in the river Teme, which passes near my re- 



VOL- XI. FABT II. 



sidence in Herefordshire, in the last winter. In a Ice- 

 morning which succeeded an intensely cold night, the ^""V ^ 

 stones in the rocky bed of the river appeared to be co- 

 vered over with frozen matter, which reflected a kind of 

 silvery whiteness, and which, upon examination, I found 

 to consist of numerous frozen spicula crossing each other 

 in every direction as in snow; but not having any 

 where, except very near the shore, assumed the state 

 of firm compact ice. The river was not at this time 

 frozen over in any part ; but the temperature of the 

 water was obviously at the freezing point, for small 

 pieces of ice had every where formed upon it on its 

 more stagnant parts near the shore ; and upon a mill- 

 pond just above the shallow streams, in the bottom of 

 which I had observed the ice, I noticed millions of 

 little frozen spicula floating. At the end of this mill- 

 pond numerous eddies and gyrations were occasioned, 

 which apparently drew the spicula under water, and 

 I found the frozen matter to accumulate more abun- 

 dantly on such parts of the stones as were opposed to 

 the current where that wag not very rapid. On some 

 large stones near the shore, of which parts were out of 

 the water, the ice beneath the water had acquired a 

 firmer texture, but appeared from its whiteness to have 

 been first formed of congregated spicula, and to have 

 subsequently frozen into a firm mass, owing to the 

 lower temperature of the stone or rock." 



The theory Here given by Mr Knight falls short in ac- Theories on 

 counting for the facts which he himself observed ; for, tl' 8 subject. 

 by supposing the spicula to have been formed at the sur- 

 face, and afterwards precipitated by the tumbling mo- 

 tions of the water to the bottom, it does not contain art 

 explanation of that congelation which must go on at the 

 bottom itself before the spicula can adhere to the stones. 

 On other occasions it is formed in places where the mo- 

 tion is far from being sufficient to send the floating 

 crystals to the bottom. It is also to be remembered 

 that, instead of such spicula as Mr Knight describes, 

 smooth and compact ice is found in these situations. 

 We would therefore observe, that water, when reduced 

 to 52, and then deprived of an additional portion of 

 caloric, though it has a tendency to freeze, yet experi- 

 ences in this respect different degrees of facility accord- 

 ing to certain circumstances. One of these is the pre- 

 sence of certain solid points or rough surfaces. Hence 

 water reduced to 2<i without freezing, immediately 

 fronts when a crystal is dropt into it, and the ice forms 

 first upon the crystal itself. Agitation also seems to in- 

 fluence it. Water, when left quite stagnant, may re. 

 main liquid, and be immediately frozen by a gentle 

 shaking. But a great degree ot agitation while it is 

 cooling seems to retard congelation, and always prevents 

 it from proceeding with regularity. Now it appears to 

 us, that in w hiris and eddies, the water at the surface lo- 

 ses a certain portion of caloric, and receives a tendency 

 to congelation, which however is resisted by the motion 

 to which it is subjected, and may be promoted in ano- 

 ther place by a slight additional aid from an external 

 cause. The motion, indeed, while it prevents the freez- 

 ing of the surface, assists that process at the bottom by 

 accomplishing the reduction of the whole body of wa- 

 ter to the freezing temperature. It is well known that 

 the temperature of greatest contraction and specific gra- 

 vity of water i* somewhere above the freezing poiifl, 

 about the 40 of Fahrenheit. While higher than 4O, a 

 reduction of the temperature at the surface, by increasing 

 the specific gravity, produces a sinking of the superfi- 

 cial portion, and an intermixture with that which is be- 

 4 M 



