HISTORY of the SOCIETY. 



1784. 



Dec. 20. 

 Efiay by Mr 



Dalzd. 



1785. 



Jan. 3. 



Mr Playfair on 

 barometrical 

 meafurements. 



Dr Blane's ac- 

 count of the 

 hurricane t- 

 Barb.icloes. 



2. FURNISH a telefcope with a plain mirror, inclined to its 

 axis in an angle of 45, and a feries of achromatic prifms re- 

 fracting 90. Suppofe the telefcope to be directed to a point 

 of the heavens, 90 diftant from a ftar which is viewed through 

 it. Suppofe alfo the earth to be at reft, and the images of this 

 flar, formed by the refracted and by the reflected light, to coin- 

 cide. Then fuppofe the earth to be in motion towards this ftar : 

 The images will feparate, both on account of a change in the 

 total deviation of the refracted light, and alfo on account of 

 a tranfverfe aberration, to which the refracted image is liable, 

 by the motion of the telefcope. 



3. IF a long achromatic telefcope be directed to a fixed ftar, 

 towards which the earth is moving, the focal diftance of the te- 

 lefcope will be lengthened. The augmentation will indeed be 

 very fmall, but Mr WILSON has fallen upon very ingenious 

 methods of increafing it, fo as to make it become fenfible. 



Lit. CI. Mr Profeflbr DALZEL read an Eflay towards an Ex- 

 planation of the Pleafure arifing from certain Scenes, Reprefen- 

 tations and Defcriptions of Diftrefs : But he did not incline 

 that the Eflay, or any account of it, fhould be given in this vo- 

 lume. 



Phyf. CL The Reverend Mr JOHN PL AY FAIR read the fe- 

 cond part of his Paper, on the Caufes that affect the Accura- 

 cy of Barometrical Meafurements, publiflied in this volume. 

 [No. HI. Phyf. Cl.~] 



Dr GREGORY read a paper communicated by Dr BLANK, 

 giving an Account of the Hurricane at Barbadoes on the loth 

 of October 1780. 



THERE had been nothing that could be called a hurricane 

 felt at Barbadoes for more than a century before 1780, fo that 



the 



