lioyal Society. 379 



Zach gave a full account of his alleged discovery, drawn up from 

 Harriot's papers ; an English translation of which was circulated in 

 this country, and has been perpetuated by its being inserted in Dr. 

 Hutton's Mathematical Dictionary. The author, having been en- 

 trusted by Lord Egremont with Harriot's original papers, has ex- 

 amined them with every attention he could apply to the subject, and 

 gives in the present memoir the result of his inquiry. 



The observations of Harriot on the spots on the sun, fill seventy- 

 four half-sheets of foolscap, the first being dated December 8, 1610. 

 These papers are in good preservation : the writing is clear, and the 

 drawings well defined. Baron Zach says, that " lie compared the 

 corresponding ones with those observed by Galileo, and found betwixt 

 them an exact agreement." This, the author shows, is very far from 

 being the case, and he also brings evidence to prove that the discovery 

 of the spots on the sun was made by Galileo at latest in the summer of 

 the year IGIO, and very probably in or before the month of July. He 

 allows, however, that Harriot's observation in December of the same 

 year, was the result of his own spontaneous curiosity. 



The first observation made by Harriot of the satellites of Jupiter, 

 has for date the 17th of October IGIO. Those that follow, extend to 

 the '26th of February 1612: they are clearly written out on thirteen 

 half- sheets of foolscap. But, even by the statement of Baron Zach, 

 Galileo di.scovered them on the 7th of January IGIO ; that is, nearly 

 tight months before Harriot. 



The author has detected many other material inaccuracies in the 

 account given to the world by Baron Zach of Harriot's observations. 

 He concludes, however, by observing that Harriot ought not to be 

 deprived of tlie credit which is justly due to him, because a greater 

 sliare has by some persons been claimed for him than he is justly 

 entitled to. He himself made no pretensions to priority in the dis- 

 coveries in question. 



May 31. — The reading of a Paper, entitled, " On tlic Correction of 

 a Pendulum for the reduction to a vacuum, together with Remarks on 

 some Anomalies observed in Pendulum Experiments," by Francis 

 Baily, Esq. F.Il.S., — was commenced. 



June 7. — The reading of Mr. Baily's Paper on the Pendulum, was 

 resumed and concluded. 



The author observes, that in all the experiments hitherto made with 

 the pendulum, a very important correction, depending on the influ- 

 ence of the circumambient air, Ifas been omitted ; and that the phi- 

 losojihical world is indebted to M. Bessel for having first drawn the 

 attention of the ])ublic more immediately to this subject. For, al- 

 though Newton evidently suspected that such an influence existed, 

 and although the subject had been since fully discussed by the Che- 

 valier du Buat, nearly .'iO years ago, yf t it does not appear that any 

 of the distinguished individuals, employed by the difl'erent Govern- 

 ments in making experiments on liie pendulum in more recent times, 

 have had any notion that the efiect of the air, on the moving body, 

 was any other than that depending on its density ; and consequently 

 varying in amount according to tlie s|)ecific gravity of the metal of 



3 C 2 



