51 



centre of the upper surface of the elastic box is a solid 

 cylindrical socket x> about half an inch high, to the top of 

 which the principal lever, c, d, e, is attached ; this lever, 

 which brings the box into a state of tension by separa- 

 ting the surfaces, rests partly on a spiral spring d, and 

 partly on two fulcrums having knife-edges, with perfect 

 freedom of motion ; the end e of the large or principal 

 lever is attached to a second lever /, from which a fine 

 watch-chain g extends to h, where it works on a drum 

 attached to the arbour of the hand ; a hair spring at h t 

 the attachments of which are made to the metallic plate 

 i, regulates the motion of the hand. 



As the weight of the atmosphere is increased or di- 

 minished, so is the surface of the corrugated elastic box 

 depressed or elevated, as is also at the same time the 

 spiral spring d y upon which the principal lever rests ; 

 and this motion is communicated through the levers to 

 the arbour of the hand at h. The tension of the box in 

 its construction is equal to 44 Ibs. At the back of the 

 Aneroid is a screw to adjust the hand to the height of 

 any standard mercurial barometer : for comparative ob- 

 servations the Aneroid must be placed in the position 

 for which the adjustment is made. 



