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XXXIII. On the Date of the Application of Telescope i to 

 astronomic Iiislruments ; the Time wlien Astronomer s fist 

 observed the Stars and Planets in the Day-time ly means 

 of these Telescopes ; and on ttie Author of these Dis- 

 coveries. Translated from the Dench of M. De Fouchy *. 



J. HE two discoveries which form the object of this rriemoir 

 are among those tliat have contributed most to bring astro- 

 nomy to its present degree of perfection. It is very singular 

 that the gratitude of astronomers has not preserved to pos- 

 terity the person's name who made them ; aild that the 

 Academy has now, al the end of a century, this omission to 

 repair; — happily it is never too late to render justice: honour 

 and gratitude do not admit of prescription. 



It was required last year to point out the author of the ap- 

 plication of telescopes instead of siijhts to instruments; to 

 determine thfc date of this inventiori; and the tiine when 

 asiron(miers first observed the planets and largest stars by 

 means of them during the dav-time. The greater part of 

 astronomers attributed one of these two useful inventions t(5 

 M. Auzout, and the other to M. Picard. As I remembered 

 to have seen these two points very well established some- 

 where in a book I had formerly read, T merely observed^ 

 that I supposed the time might be obtained very nearly ; 

 and the Academy requested me to endeavour to find what I 

 could on this subject : — The following is the result of my re-* 

 search. 



The late M. de la Hiref gave in 1717 a memoir entitk'd 

 Inquiries respecting the Dates of the Invention of the Mi- 

 crometer, of Pendulum Clocks^ and of common Telescopes. 

 As I knew that he had spoken in this memoir of some other 

 astronomic inventioiis, I wished to see if he had not men- 

 tioned this. I found (hat he could neither discover the 

 exact time nor the name of the author of this invention j 

 that he spoke of it to M. Ficard, who merely told him that 

 M. Auzout had some concern in it; which agrees very well 

 with what Picard said himself at the beginninu; of his 

 Treatise on the Measure of the Earth, — that the idea of ap- 

 plying telescopes instead of siiffits to instruments^ had been 

 thought of for some lime. A'i. de la Hire adds also, thAt hd 

 had searched the Phdosophical Transactions nithout having 

 found any thing relating to the purpose. 1 therefore took 



• Read to the Royal Acnilemy of Scicrites at Paris, 12th ot November, 

 n:i, niid pii|j|i>-Iied in the Memoirs lor 1787. , 



t Memoirs for 1717, paje 78. 



Vol. 34. No. 139. October I8O9, Q the 



