448 Prof. Challis on the Hydrodynamical 



ellipticity seems to be such-and-such ; but this is not to be taken 

 as any proof of such ellipticity. The idea was not his, either. 



One remark more, and I have done. Kater is recognized, 

 and Borda — the one in speaking of "Kater's pendulum," and 

 the other in alluding to " Borda's method of coincidences " — 

 which, by the way, was not any more peculiarly Borda's than 

 the formula (as given) was Clairaut's ; Clairaut's name also 

 is mentioned, as we have seen ; not a single other author or 

 experimenter in this field is mentioned from the first line to 

 the last. Surely this is carrying " originality in experimental 

 research" too far — even to the very verge of decency. I 

 would suggest to the students of the Japanese college that 

 they return to the discarded convertible pendulums, and de- 

 mand to know, as a matter of scientific interest, why their 

 results were so unsatisfactory. They may rest assured that it 

 was because they had neglected some of those precautions and 

 reductions which " well-known experiments " are especially 

 useful in inculcating. 



No experimental result is worth publishing which does not 

 carry with it direct or indirect evidence of reliability — or the 

 means of correcting its errors. In the present case we have 

 neither the one nor the other. The force of gravity at Tokio 

 in Japan may be known more certainly from the above for- 

 mula than from the experiments recorded in the paper under 

 review. 



I am, Gentlemen, 



Yours truly, 



J. Herschel. 



LX. Supplement to Researches on the Hydrodynamical Theory 

 of the Physical Forces, including a Theory of the Microphone. 

 By Professor Challis, M.A., F.R.S., F.R.A.S* 



WHEN I wrote the article on Newton's " Eegula Tertia 

 Philosophandi," inserted in the Philosophical Maga- 

 zine for January 1880, I supposed that I should not have 

 occasion to say more relative to the hydrodynamical theory of 

 physical force. As, however, I have since discovered that some 

 points of considerable importance have been either insuffi- 

 ciently explained or altogether omitted, I propose to supple- 

 ment the previous researches by the subjoined corrections and 

 additions. 



( 1) In the first place, the postscript to the above-mentioned 

 article, which was written and despatched somewhat hastily, 

 requires to be corrected by the following considerations. 

 * Communicated by the Author. 





