[ lot ] 



time leave the greateft poflible room for the reception of the 

 falling quickfilver. 



R E M A R K II. 



On the Adjujiment of the Injlrumcnt. 



This Inftrument is adjufted, once for all, at the time of making 

 it, in the following manner : 



Measure very exadly the inner diameter of the ivory cylinder, 

 which fhould be turned throughout perfedly true ; the infide 

 of the cover very fhallow and of the fame dimenfions with the 

 reft of the cylinder. You are likewife to meafure the diameter 

 of the aperture of the glafs tube, which fliould be alfo chofen 

 truly cylindrical and well drawn. Thefe diameters being known, 

 a very eafy calculation will fliew what the corredlion of the fcale 

 muft be within any afligned limits ; that is to fay, what the 

 elevation of a fluid in a cylinder of one inch diameter will be by 

 pouring into it the contents of another cylinder of one-tenth of an 

 inch in diameter, and three inches or any other given quantity in 

 height. There will in the prefent cafe be required another cor- 

 redion (viz.) an allowance for the fpace occupied in the cylinder 

 by the projeding part of the glafs tube. Thefe calculations being 

 made for every particular barometer, its fcale fhould be accom- 

 panied 



