POSITION OF DOUBLE STARS, 



267 



Otf^rvations 

 and Inferences 

 refpefting the 

 changes of rela- 

 tive fituation in , 

 ftars extremely . 

 near each other. 



As a confirmation of the accuracy of thefe obfervatjons, we 

 may have recourfe toa pofition of the lame ftars, deduced from 

 the places of them, as they are given in Mayer's Zodiacal 

 Catalogue. By two obfcrvations reduced to the beginning of 

 the year 1756, the preceding one was S'^S before the other in 

 right afcenfion, and 5'^3 more north than that ftar. From this 

 we calculate the petition, which was 54** 21' 37'^ north pre- 

 ceding. The interval from the ift of January, 1756, to the 

 21ft of November, 1781, is 25 years and 325 days. When 

 this is added to the period I have given, we have 47 years 

 and 105 days, for a motion of 24^ 2^ The annual motion, 

 deduced from this lengthened period, which is 30',5, differs 

 lefs than 1^ minute from that which has been calculated from 

 my obfcrvations. With the affiftance, therefore, of Mayer^s 

 obfcrvations, which greatly fupports our calculation, we may- 

 conclude, that the two ftars of y Virginis revolve round each 

 other in about 708 years. 



Account of the Invention of the Compound- Barrel and Winch, 

 and its ufeful Application on a Large Scale, In a Letter from 

 Afr.J. J. Hawkins. 



To Mr. NICHOLSON. 



SIR, 



IN No. 25 of your ufeful Journal, p. 50, you mention the 

 compound-barrel and winch, as the invention of the celebrated 

 Mr. George Eckhardt. 



Not in the leaft wiftiing to frbtrad from the well known in- The compound 

 ventive talents of that Gentleman, I beg leave to fay, that, t^alfotn-*"'^ 

 if it was invented by him, it was alfo invented to my certain vented by Mr. . 

 knowledge, by the late Mr. Robert Mc Kean of Philadelphia, ^* ^*^ ^^^' 

 fon to the prefent governor of Pennfylvania. 



4 Mr. 



