iy2 CORRESPONDANCE. 1 664. 



N= 1289. 



[R. Hooke] à [R. Boyle]. 



25 DÉCEMBRE 1664. 



La lettre a été publiée dans „Iioylc''s IForks , Fui. F." 



December 15. 1664. 

 Moll honoured Sir 



This letter ') coming fo late to the pofthoufe on Tucfday night, was brought 

 back to me, fince which I hâve made farther trial of Monfieur Zulichem's experi- 

 ment, and both my lord Brouncker, Sir R. Moray and Dr. Wren, were judges and 

 cxaminers of the experiment, and find, that the trials made with thefe pendulums, 

 vvhofe balls were of ligniim vitae, did not anfwer to Mr. Zulichem's rulc, and there- 

 fore it is nowmuch doubted of 0- We had yefterday in feveral parts of England, an 

 account of the appearance of a very great comet^) in the foiith fouth-eafl:, with a very 

 long tail, extended towards the north-weft; fome fay about ten yards long, fome 

 about two; but how much that is, is difficult to guefs, unlefs we could fce it, which 

 I hâve done ail this lall: night, but to little purpofe, by reafon of the thicknefs of the 

 air. It has been feen in Yorkfhire, and in Chefliire, and at Portfmouth^), and feve- 



') Voir la Lettre N°. 1288. 



^) Dans les „Proceedings" de la séance du 14 décembre 1664 (V. st.) on lit, au sujet de ces 

 expériences, ce qui suit: 



The experiment of Monfieur Huygens for the univerfal meafurc was repca- 

 ted twice; and the firfl: time the ftring of the biggeft bail (which was offix 

 inches diameter) was 2 feet 1 1| inches long; and that of the fmaller bail was 

 3 feet li inch long. The prefident having calculated the proportions, accor- 

 ding to Monfieur Huygens's rule, found them vary from it y%, the ftring of the 

 fmaller bullet being y% longer than it fhould be, according to that hypothefis. 

 In the fécond trial the différence was y et greater, viz. -'g or -^^ or ^^^^ which 

 was thought too confiderable a différence for a fl:andard. 



It was thereupon concluded that there mufl: be either fome miilake in the 

 rule, or fome fault in the experiment. 



The prefident hinted, that the différence of the air and the bullet might 

 vary the lenght of the line So that a fmall bullet in a clear air, and a great bul- 

 let in a thick air, would caufe différent meafures. 

 3) Les éléments de cette comète à mouvement rétrograde , qui passa à son périhélie le 4 décem- 

 bre 1664, ont été calculés par 



Halley „Aftronomiae Cometicae Synopfis" (Philos. Trans. 1705) et par 



L. L. Lindelôf, De Orbita Cometae anni 1664. Helsingforfiae. 1854. 

 '*) Par lord Sandwich, qui se trouvait à bord du vaisseau „London." 



