286 



Art. VII. Examination of the Large Achromatic of the 

 Royal Observatory at Paris. 



Extract of a Letter from James South, Esq., F. R. S., to 

 M. Schumacher. 



Dear Sir, Passy, prh Paris, 1 825, Sept. 6. 



1 have the honour to transmit you the enclosed which I have 

 received from Mr. Herschel. I have hitherto been prevented from 

 doing much in the way of ordinary astronomy, by a resolution to 

 complete my observations of the double stars ; and I am glad to 

 say, that my labours in this department of astronomical science 

 are (at least for the present) fast drawing to a close. By the 

 latter part of October next, I have little doubt but that my ob- 

 servatory at this, place will be dismantled ; and it is my intention 

 to present the observations of 400 additional double stars to the 

 Royal Society, at its first meeting in November. 



From your Astronomische Nachrichten, and subsequently from 

 the Memoirs of the Astronomical Society of London, I am glad to 

 find that the Dorpat Achromatic realizes the expectations of its 

 possessor ; and I rejoice very heartily that it has fallen into such 

 hands. Mr. Struve will not allow it to remain idle. 



In the accompanying communication from Mr. Herschel, allu- 

 sion is made to the achromatic constructed by Lerebours, now 

 placed in, and belonging to, the Royal Observatory of Paris ; 

 perhaps a few lines devoted to it, will not be altogether unin- 

 teresting. 



The diameter of its object glass uncovered by the cell (in 

 English measure), is rather better than 9.2 inches, of which 8.4 

 inches only are in actual use ; its focal length is 1 1 feet. The 

 magnifying powers with which I used it, on the night of the 15th 

 of March last, are 136. 153. 224. 240. 420. and 5G0. With all 

 except 560 (which by some forgetfulness was not applied,) Venus 

 was extremely well defined during dark night ; of course, Jupiter 

 and Saturn were well shewn. The two stars of Castor, of y Leo- 

 nis, of £ Orionis, were exhibited with 240, 420, and 560 as round 

 as possible : « Leonis presented by its side a light blue star with 



