I'OPULAR SCIEi^CE NEWS. 



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iSSy, 



manner of tuitk's, at the time of its death, the 

 task of removing the fossil from its stony 

 matrix was one of no small dirticulty. Jt 

 was finallv accomplished, however, and the 

 thousand or more pieces into which it had 

 been separated in the jsrocess were carefully 

 joined together, making a most unique and 

 valuable paleontological specimen. 



The tortoise resembles, in many respects, a 

 species which has recently become extinct in 

 the island of Madagascar ; and the other fossil 

 remains which have been found in the strata 

 near Ferpignan are more or less tropical in 

 type, and indicate a much wanner climate in 

 the pliocene age, which gave way to the cold 

 and ice of the glacial period before the more 

 temperate climate of recent times was finally 

 established. 



-^♦► — 



SEA-WATER AND SEA-WATER ICK. 



BY \V. A. ASHE, F. R. 



Sea-water is variously stated 



A. s. 



as fret'zinsr at a 



lower than that of its molting point. The only 

 way to arrive at a proper. determination of a value 

 of the freezing point of any liquid, is by recording 

 the loAvest point attained whilst a mass under slight 

 agitation is being transformed into its ice, unless in 

 the case where no-chemical change has been under- 

 gone during the transformation. Let me put this 

 conclusion of mine beyond question, by an exam- 

 pie. 



In Hudson Straits, when the ice is first formed in 

 tidal waters, that portion of it that is left aground 

 above low-water mark, freezes to the bottom, the 

 temperature of the air being below that of the freez- 

 ing-point of the water, so that on the waters rising 

 again it is left there submerged. This formation of 

 a film of ice at the surface of the water and the 

 freezing of it to the film last submerged, goes on till 

 the whole outline of the coast is transformed, by the 

 building of a wall of ice from low to high-water 

 mark, with a perpendicular face seawards.' This 

 transformation yyould not be possible, if there were 

 agreement between the freezing and melting points 

 of sea water. Let me explain the order and nature 

 of the proceeding. 



In the first place it is essential that the tempera- 

 ture of the air should be below that of the freezing- 



temperature from 28^ to 

 28.8^. Experiments that 

 were undertaken by the 

 1 ludson Bay Expedition 

 of 18S5 proved that its 

 freezing point was at 

 26.7° — all temperatures ||1|] 

 being expressed in ac- 

 cordance with the Fareri- 

 heit scale. 



This discrepancy can 

 onU'be accounted for on 

 the supposition of there 

 being a difference be- 

 tween the freezing and 

 melting points of sea- 

 water. That the values 

 first above given repre- 

 sent the temperature ( 

 its melting point, tlio 

 latter of the freezini.; 

 point proper, seems evi- 

 dent. In general, the 

 freezing point of water, 

 both fresh and salt, is de- 

 termined by an admixture of water with its ice and 

 the agitation of the two until thermic equilib- 

 rium between them is attained, when the the tem- 

 perature that the mass is then at, is accepted as that 

 of its freezing-point. It is not unreasonable to sup- 

 pose that, in the case of fresh water this condition 

 of thermic equilibrium is really reached at the 

 freezing-point of the mass, because the chemical 

 combination of the water and its ice is identical. 

 But, in the case of sea-water and its ice, there has 

 has been a change produced in the transformation, 

 whereby four-fifth.s of the saline particles have been 

 excluded from the ice. No one will question the 

 statement that thermic equilibrium between sea- 

 water and fresh-water ice, or the opposite, would 

 represent either the freezing point of sea or fresh 

 water. Yet it has been assumed that ice which no 

 longer contains the constituents of its water, (more 

 closely agreeing with that of fresh than sea water), 

 will melt at the same temperature that it was frozen 

 at, quite forgetting that this expelling of saline par- 

 ticles was not performed without the loss of some 

 energy; and, as the only energy that is present in 

 our mass is heat, this transformation was only per- 

 formed at a loss from this source; and that in con- 

 sequence, the freezing point of tea water must be 



point of sea water; and in the next place, it is evi- 

 dent that the temperature of the earth forming the 

 bottom, must be above the freezing-point, orelse ice 

 would form there ; still, it need not be much abo\e 

 it. as the water, being very nearly at the tempera- 

 ture of its freezing-point, would reduce the surface 

 of the bottom to that point, less the increase in 

 temperature consequent on the convection of the 

 earth's heat to that surface. The freezing-point of 

 sea-water being 26.7'', the melting point 28. S", and 

 the temperature of the bottom being assumed as 

 being between these values, (a not. improbable as- 

 sumption, after the reasons given) we can under- 

 stand that when the ice is placed in contact with it 

 by the falling tide, the temperature of the air, re- 

 duces the water, which is running off the ice as the 

 tide leaves it, so that freezes and cements the ice to 



! the bottom. To free the ice again would require, 

 either that the temperature of the air or water 

 should rise above 28.8'^ which, Avith the water at 

 26.7° and the atmosphere below this point, is not 

 possible; therefore the ice remains fast to the bot- 

 tom. 



Fresh water freezing, and its ice melting at the 

 same temperature, it cannot freeze to the bottom ; 



I for, granting that the temperature of the water may 



be 32°, that of the bottom must be above, both on 

 account of the water in contact with it being at a 

 higher temperature than this, and because, even 

 I if we assume the temperature of the whole mass 

 of water as being 32'^", that of the bottom must 

 j be above this, owing to convection, as before stated. 

 : Anchor-ice does form in fresh water occasionally. 

 ; but not on the bottom proper, as it attaches itself to 

 bowlders or pebbles which are not themselves in 

 perfectly continuous connection with the bottom, 

 and are therefore largely siu'roundcd by the water, 

 and correspondingly affected by its temperature, 

 w-hilst insensibly affected liy convection: so that if 

 we cark assume conditions under which the water's 

 temperature would be below the freezing point, we 

 I have those cases in which anchor-ice will form. In 

 j no other way is it possible to account for the freez- 

 ing of sea-water ice to the bottom than bv the as- 

 sumption of a difference between its freezing and 

 melting points. 



Fresh water always freezes at the surl'ace first; 

 sea-water, during cold, calm weather is converted 

 into ice at some point beneath the surface, for then 

 the ice-spicules are seen rushing with the momen- 

 tum they have acepiired from their increased vol- 

 ume and consequent less specific gravity than the 

 water, from their posi- 

 tion of formation to the 

 surface where their nio- 

 nientmn is generall\ 

 ^utiiciently great to per- 

 iiiil of their thrusting 

 ihenisches some dis- 

 lance beyond this sur- 

 face, when, falling back 

 ;o it again, they aggre- 

 uato into a surface film. 

 Iiuler tliese conditions 

 nl' cold and calm, the 

 I'lrniation of sea-water 

 ice proceeds indifterent- 

 ly as to position : but 

 if. as is generally the 

 case, there is any wind 

 blowing the permanent 

 formation takes place 

 I'rotn the windwartl 

 .--liore in tlie form of long, 

 narrow •■ streamers. " 

 which, starting witli 

 a width of a tew 

 yards, may reach a length of three or four hun- 

 dred; in the meantime, adjacent • streamers" swa\- 

 ing towards each other under the influence of the 

 wind, become joined and the whole surface evcnt- 

 iu:lly covered. The cf)heNion ot' the iiarticles must 

 necessarily be very great to withstand the strain 

 that the mass is under whilst in this exaggerated 

 form, under the influence of the wind that is blow- 

 ing and the small, though quite sensible ripple of 

 the surface. 



'I'hc specific gravity of fresh water increasing to 

 a certain lower temperatere. then decreasing to the 

 freezing-point, permits of its ice being formed at 

 the surface. In the case of sea-water, as the ice 

 does not form at the surface, it is evident that its 

 density must increase to the freezing point, when 

 the increase in its volume, consequent on its trans- 

 formation into ice, brings it to the surface. .Such 

 an assertion would seem to allow of the conclusion 

 that sea water ice must form from the sea bottom 

 where, becoming fast to it, subsequent freezings 

 would eventually t'orm a solid mass from the bottom 

 to the siu'tace. This is luidoubtedlv a fair conclu- 

 sion, if we ignore the fact that although the water 

 at the bottom is at the freezing-point, the bottom 

 itself mu.st be above tbi* temperature owing to the 



