Jan., 1893 CORRESPONDENCE. 79 



[Dr. de Varigny brings forward the statement that "we possess, in the facts of 

 domestication," &c., in support of his view that Professor Weismann goes too far 

 when he asserts that we have no proof of the direct production of transmissible 

 changes by means of external influences. As used, the sentence amounts to a single 

 statement that we know many cases of variations due to environment being trans- 

 mitted. 



The whole controversy to which Dr. de Varigny is alluding, concerns the state- 

 ment which he brings up as an argument on one side of the controversy. 



In the matter of Le Conte, I am sorry that I attributed to Dr. de Varignv an 

 approval he now disowns. He wrote (p. 229) : — 



" What can the methods of experimental transformism be? The only answer 

 to this question is based on the consideration of what the factors of evolution are, or 

 are supposed to be. At the present moment five are usually recognised. I quote 

 from Le Conte' s able paper of recent date." 



In the two "factors" I quoted in my review, Le Conte runs together the 

 observed facts of phylogenetic variation and phylogenetic decay of disused parts, 

 with the theory that the result of the action of environment is inherited and integ- 

 rated. A chief object of " e.Kperimental transformism" must be to decide on these 

 theories, and any " method" involving preliminary acceptance or rejection of them 

 is valueless. 



I do not consider Dr. de Varigny's statements heretical, but if I did it would 

 be of no interest to anyone. I merely showed that they were confused. 



P. C M.] 



The Interior of the Earth. 



In thd summary of my late paper in the Pyoc. Cambridge Phil. Soc, given in 

 " Notes and Comments " of December, there are two points to which I wish to be 

 permitted to refer. It is stated that I have "reinvestigated mathematically " the 

 effects of a tidal yielding of the earth on a tide of short period, according to the 

 canal theory. Professor Darwin had already made that investigation, and there 

 was, consequently, no need to do it over again. But he had left his result in the 

 form of general symbols, and what I have done is to carry his calculation a step 

 further by substituting for the symbols their known astronomical values. It was in 

 this way that I arrived at a conclusion to what extent the ocean tide might be 

 expected to be diminished if the interior of the earth is liquid. 



The Reviewer has, however, given my result incorrectly in saying that I have 

 found that the tide, in the case of a liquid interior, "would be about two-fifths of 

 what it would be " in the case of the earth being solid. What I did say was, that 

 it would be diminished by two-fifths if the earth was taken as homogeneous, but only 

 by one-fifth when the fact is taken into account that the outer parts of the earth are 

 of half the mean density. This, of course, will leave four-fifths of the height on a 

 solid earth for the height on a liquid earth. For instance, if the height of the tide 

 from highest to lowest on a solid earth were fifty inches, it would still be forty 

 inches if the interior were liquid. Since we do not know what the exact height of the 

 tide would be on a solid earth, it is perfectly possible that the tides actually expe- 

 rienced may be of the height appropriate to a liquid interior, seeing the diminution 

 caused by liquidity to be so small. 



On a review of the whole question, it appears to me that what had been pre- 

 viously done by Lord Kelvin and Professor Darwin, and other mathematicians, had 

 been to show that, unless the earth is excessively rigid, the tidal forces must deform 

 it. But it had been assumed that, if so deformed, it would carry the water up and 

 down with it, so that the ocean (ides would not be noticeable; but the question 

 whether or not this assumption was valid, had never, so far as I know, been brought 

 to the test of numbers until I made the attempt. 



O. Fisher. 

 Harlton, Cambridge, December 12, 1892. 



