"274 



PRINCIPLES OF THE MECHANICAL THEORY OF HEAT. 



tare, the water froze, and thereby the copper index was fixed at the place which 

 Fig. 16. it occupied. The ni})ple of ice formed by the freezing of the water 

 in the conic space at c was removed, the copper cone / introduced, 

 and by means of the screw C driven in as strongly as possible. The 

 whole apparatus was now again reversed, so that E was above and 

 C below. 



After the apparatus, in this last position, was firmly secured in a 

 strong cross-piece between two bars, (Fig. 17,) and suiTOunded with 

 the freezing mixture, the index d being thus plunged in the ice deep 

 under g, the female screw or nut E was, by means of a lever six 

 decimetres long, gradually driven around, and thereby g more and 

 more pressed downward. If the ice remained firm under the com- 

 pression, there must, on the opening of the screw C, situated below, 

 appear at the copper cone/ first a cylinder of ice and then the index 

 d; but if water has been produced by the pressure, the index d must 

 descend to c, at the lower end of the cavity, a^id hence, on the with- 

 drawal of/, first th e in- 

 '"■ ■ dex and next in order 



S? the massive ice cylin- 



wmiimiimgii¥rai» der respectively make 

 their appearance. 



In order to prevent 

 the heating of the 

 apparatus by me- 

 ^" / chanical work the 



^__^ • .^ii_^ depression of g was 



'"^^ -•■ ■ ^" ^gj.y sio^YJy conduc- 



ted, the female screw E being turned only every five minutes to the extent of 4/)°, 

 and the operation being thus protracted through the space of some four hours. 

 "When, after these processes, the lower terminal screw was opened, still under a 

 very low temperature, the copjier cone /immediately protruded and ice instantly 

 formed on its sides. Directly behind the cone/ followed the index f?, and after 

 this a tliick cylinder of ice, which must have been formed at the moment of the 

 opening. 



Thus was the proof afforded that, hy a sufficlcnUij strong pressiire, ice is coit- 

 verted into water a^J = 18° C. The pressure to which the ice was subjected in this 

 experimeut is estimated by Mousson at some 13,000 atmospheres. Tliis lowering 

 of the melting point of iee through pressure plays an important part in the expla- 

 Dation of glacier-phenomena, and on that account will be again the subject of con- 

 Bideration in the section of cosmical physics. 



The value of ^^ (in equation 111) is, for water, a negative one, because ice, in 

 melting, contracts. For such substances, however, as are attended in melting 

 with an augmentation of volume, is positive, and for tliese therefore the melting 



\ 



> 



