214 Mr. C. Y. Boys on an Addition to 



chison even held the view that at an early period of the earth's 

 history there were no great mountains *. We have ample 

 grounds for believing neither view to be correct. 



Prof. Bonney, in a Note appended to Mr. Davison's paper, 

 attempts to further elucidate the geological results that would 

 follow from this view of the effects of the earth's contraction. 

 I am sorry that I am unable to agree with his suggestions. 

 When I wrote the chapter referred to I felt, if the views 

 there expounded were admitted (which they practically are by 

 Messrs. Davison and Bonney), that they were fatal to the 

 Contraction-theory of Mountain-building ; I think so still. 



In what way, I may ask, could gneissic axial cores, having 

 the fan-structure which characterizes most great mountain- 

 ranges, have been forced up and the overlying beds thrown 

 back upon themselves, if the tangential compression, gradually 

 diminishing downwards, did not extend five miles vertically 

 into the earth's crust? for during the early periods of mountain- 

 making the depth of crust under compression must have been, 

 according to Mr. Davison, much less. 



For myself I go much further, and say that such axial cores 

 and other phenomena of mountain-ranges which I have else- 

 where dealt with at length, cannot be satisfactorily accounted 

 for except on the hypothesis, within certain limits, of the 

 compression increasing, not diminishing, with the depth. 



To illustrate these effects I made a series of experiments 

 which are partially detailed in pp. 331-333 and plate 42. ' 

 Although we differ radically in some important particulars, 

 I welcome Messrs. Davison and Bonney's theoretical investiga- 

 tions, as truth cannot but gain by the friction of various ideas. 



XXIV. On an Addition to Bunsen's Ice- Calorimeter. By 

 C. V. Boys, A.B.S.M., Demonstrator of Physics at the 

 Science Schools, S. Kensingtonf. 



IT is probable that no single instrument has excited so much 

 admiration on the part of physicists as Bunsen's calori- 

 meter ; its beautiful simplicity, its marvellous sensibility, and 

 its accuracy in skilled hands place it in the first rank among 

 instruments employed in investigations for which it is avail- 

 able. In our uncertain climate, however, it is not often found 

 in actual use ; for unless a large supply of perfectly pure snow, 

 free from all saline contamination, can be obtained, it cannot 

 be employed to its fullest advantage, and because possibly 

 according to Bunsen's directions, it should be used in a room 

 not much above the freezing-point. 



* ' Siluria,' fifth edition, p. 498. 

 t Communicated by the Author. 



