xxiv BIOGRAPHICAL MEMOIR 



say, "We don't talk about it in this room." He amused 

 himself also with mathematical investigations, which he was 

 able to carry on in a remarkable manner, without paper or 

 figure, "in his head," as the common phrase is. It was in 

 this way that he discovered for himself what he believed to 

 be a new view of Napier's rules for the solution of right- 

 angled spherical triangles. His discovery involves so curious 

 a piece of history that I shall venture for a moment to dwell 

 upon it. Ellis found out in his illness, that Napier's rules, 

 instead of being, as they have been stated to be in Cam- 

 bridge books, from Professor Woodhouse downwards, a mere 

 memoria techmca, were all capable of being deduced from one 

 geometrical construction. He sent me a paper which he dic- 

 tated on the subject, and which I requested him to allow me 

 to communicate to the Cambridge Philosophical Society. Hav- 

 ing gained his permission, I thought it well to examine the 

 literature of the subject, and above all to see what Napier 

 had himself said. On turning to Napier's famous tract, Miri- 

 fici Logarithmorum Canonis Descriptio, I found that Ellis had 

 in fact rediscovered Napier's own original conception of the 

 problem. 



It was during his illness that he dictated his remarks con- 

 cerning the construction of bees' cells ; 1 believe also that he 

 thought out at this time his demonstration of the tautochronous 

 quality of the cycloid. Indeed he had usually some mathe- 

 matical question running in his head, which served him for 

 recreation during his easier moments. Nor were other subjects 

 excluded; it was in this season of extreme bodily weakness 

 that he corresponded with the late Dr Gilly on the Eomaunce 

 language, discussed the date of the "Noble Lesson," and criti- 

 cized Dr Gilly's edition of the Yaudois Gospel of S. John. I 

 have also before me a considerable number of letters dictated to 

 friends, dealing with subjects so different, according to the tastes 

 of the persons to whom they were sent, that it seems difficult 



