VOL. XXXVII.] PHILOSOPHICAL TRANSACTIONS. 565 



omitted ; for then it will be easy to keep the plane of the instrument so near 

 that of the beforementioncd great circle, as not to want any, if the situation of 

 that circle be known : if it be not, the observer, when he sees the two objects 

 together, may turn the instrument on the axis of the telescope, till he finds 

 that position of it by which he obtains the least angle ; and this, if the specula 

 are set truly perpendicular to the plane of the instrument, will always happen 

 when the objects appear to coincide in the line gh, as expressed in fig. 3, 

 pi. 13. 



In N° 420, a rule is given for finding to which hand of the observer the ob- 

 ject seen by reflection ought to lie, but is restrained to the particular form of 

 the instrument there described. The general rule is, that when the index is 

 brought to the beginning of the scale (i. e. to 0° when the instrument is designed 

 for angles under QO", or to 90° when it is designed for angles from gO° to 180°) 

 if then a line be conceived to be drawn on it, parallel to the axis of the teles- 

 cope, or line of direction of the sight, so as to point towards the object seen 

 directly ; which ever way this line is carried by the motion of the index along 

 the arch from 0° towards 90" in the first case, or from 90° towards 180" in the 

 second, the same way the object seen by reflection ought to lie from that which 

 is seen directly. 



Ephemerides Meteorologies, Barometriae, Thermometricie, Epidemics, Mag- 

 netics, Ultrnjeclincp, conscripts cl Pelro ran Muschenbroeh, L. A. M. Med. 

 et Phil. D. Phil, et Mathes. Profess, in Acad. Ultraj. Anno. 1729. 

 N°425, p. 357. 



May be consulted in this author's works. 



A Discourse concerning the difficulty of curing Fluxes, written occasionally on. 

 reading Dr. de JussieiCs Memoir in the History, &c. of the Royal Academy of 

 Sciences in Paris, for the Year 1729. By IVilliam Cockburn, M.D., F.R S. 

 and of the Coll. of Physicians, LoJidon. N°4'25, p. 385. 



There is nothing in this paper sufficiently interesting for republication. 



An Account of a Comet seen Feb. 29, 1731-2. By Mr. John Dove. 

 N°425, p. 393. 



Feb. 29, at about half an hour past 10 at night, being in lat. 34° 28' south, 

 and long. ll^SS' west from Cape Bonne Esperance, the moon shining very 

 bright, being near the full, they saw something very bright rise about west, 

 which Mr. Dove judged to be a comet : it set about east, passing from west to 



