294 William Stevenson. By Professor Duns. 



Scoulari. When otlier fragments were forwarded Mr Stevenson's 

 guess was found to be correct, and the form was named JEury- 

 pterus Sfevensoni. 



A subject in Speculative Geology, which has ever had a charm 

 for students in whom a strong imagination is found united to 

 good attainments as workers and observers, early cast its spell over 

 Mr Stevenson. I refer to the hypothesis of the original fluid 

 condition of the whole earth, and of its present internal condition. 

 Field workers are necessarily much alone and have strong induce- 

 ments to take to waking dreams. Besides, accurate knowledge of 

 things ever tempts to enquiry after the thoughts which underly 

 them. Indeed, the whole bent of recent science is dissatisfaction 

 with the mere observation of phenomena, and an earnest desire 

 to find the laws of which they are the expression. Had Mr 

 Stevenson been satisfied with dreams without seeking their inter- 

 pretation, and with hypotheses without attempting to render them 

 into the form of laws, he would have escaped, perhaps, the 

 greatest disappointment connected with his scientific work. 

 Among his MSS. is an elaborate paper entitled " Calculations, 

 &c., relating to the Internal Fluidity of the Earth, " 1845. It is 

 loaded with complex calculations, marked by much shrewdness 

 and fair inductive power. But there are inaccuracies in the 

 calculations, and mistakes as to the import and value of phenom- 

 ena appealed to as illustrative proofs. Some of these errors are 

 corrected in subsequent copies, but after a careful perusal of the 

 paper, one finds it impossible to dissent from the criticism of 

 Professor Hopkins to whom he had sent it : 



" Cambridge, 



Dear Sir, ' Feb. 23, 1853. 



The subject which, you have discussed in the paper you sent me ha8 

 been frequently discussed before. And I am satisfied that neither further 

 discussion of it nor numerical calculations respecting it, can be of any use to 

 geology, unless conducted with far more mathematical accuracy than you 

 have pretended to in these researches Hitherto mathematicians have been 

 deterred from attacking the subject more determinedly, I imagiue, by the 

 want of the essential experimental data to give practical value to their results. 

 The effect of great pressure on the temperature of fusion of any substance, 

 the degree in which it contracts or expands in the act of passing from the 

 fluid to the solid state, the modification produced by great pressure or the 

 rate of contraction of volume from loss of heat &c. , &c. , are points to be 

 more or less approximately determined before we can enter with any hope of 

 practical success on the general problem I am now endeavouring, in con- 

 junction with Mr Fairbairn and Mr Joul of Manchester, to supply some of 

 these experimental data as far as they are attainable by direct experiment. 



