Prof. W. G. Adams on a new Polariscope. 13 



of about 100 feet in length of the above diameter per minute. 

 We have thus 393,906 foot-pounds of work done upon the lead 

 per minute, dividing which by J we have 510*2 British units of 

 heat developed per minute from the transformed work. In the 

 actual machine the whole of this is ultimately dissipated and 

 lost ; but if none of it were dissipated, as the cylindric block of 

 lead of 8*5 in. diameter by 0*416 ft. (5 inches) weighs 116*3 lbs., 

 and the specific heat of lead is = 0029 (or perhaps a little 

 more at 400° Fahr.), it follows that the heat developed by its 

 deformation from the short cylindric block of 5 inches length 

 to a rod of about 100 feet length, is enough to raise the tem- 

 perature of the lead through 151° Fahr., or, were no heat lost, to 

 raise its temperature from 400° to 551° or thereabouts — that is, 

 within about 50° of its melting point. If, therefore, we could 

 by a reverse process squeeze the 100-foot rod back into the 

 original block of 8"*5 x 5", we should find the lead in the latter 

 not only liquid, but considerably above its temperature of fusion, 

 or at nearly 700° Fahr. It is obvious, therefore, that any viscous 

 or plastic body such as lava, continually forced through apertures 

 varying in area and form and suffering continual deformation, as 

 when forced through a volcanic tube or vent, must have its tem- 

 perature continually exalted so long as it continues thus to be 

 urged forcibly forward, assuming, as is very nearly the truth in 

 nature, that an extremely small proportion of the heat developed 

 in the process can be dissipated by conduction to the walls of the 

 tube. 



The preceding remarks apppear to the writer sufficient to 

 show that there is no physical difficulty in the conception in- 

 volved in his original memoir (Phil. Trans. 1873), but not there 

 enlarged upon in detail, that the temperatures consequent upon 

 crushing the materials of our earth's crust are sufficient locally 

 to bring these into fusion. 



II. A new Polariscope. By Professor W. G. Adams*. 



IN devising this instrument, the principal objects in view have 

 been : — 



(1) To obtain an extensive field of view. 



(2) To afford a means of measuring the rings and the angles 

 between the optic axes of biaxal crystals. 



(3) To have a means of immersing the crystal in a liquid in 

 those cases in which the optic axes are too far apart to be seen 

 in air. 



* Read before the Physical Society, May 22, 18/5. Communicated 

 by the Society. 



