II 



195 



Propionyl-series. Succinyl-series. 



Propionic acid. . C 2 (C 4 H 5 )^ j O 2 Succinic acid. . C 4 (C 4 H 4 )O 4 ( 



Anhydrous pro- C 2 (C.H.)O 2 1 ^ Anhydrous sue- r- /n TT \r> r 

 picnic acid. C 2 (C 4 H 5 )0 2 / ^ cinic acid. C 4(C 4 H 4 )O 4 ,O 2 



rn 



Propionylamide N< H Succinamide. 



IC 2 (C 4 H 5 )0 2 



VII. "Description of an Instrument for registering Changes 

 of Temperature." By BALFOUR STEWART, Esq. Com- 

 municated by J. P. GASSIOT, Esq., F.R.S., Chairman of the 

 Kew Observatory Committee of the British Association. 

 Received June 12, 1856. 



It lately occurred to the author that advantage might be taken of 

 the capillary action of mercury to construct an instrument similar to 

 a thermometer, but in which the mercury should expand from heat 

 only in one tube, and contract from cold only in another. Accord- 

 ingly a bulb was blown between two thermometric tubes of differently- 

 sized bores, in such a manner that the tubes lay in one straight line, 

 with the bulb between them. The bulb was then filled with mer- 

 cury, and the tubes were hermetically sealed at both ends, having 

 been first carefully deprived of air. When the instrument thus con- 

 structed was laid in a horizontal position, or nearly so, its action was 

 precisely what the author had hoped ; the mercury contracting from 

 cold only in the narrow bore, and expanding from heat only in the 

 wide one, even when viewed by a microscope of considerable mag- 

 nifying power. 



It was suggested by Mr. Welsh, Director of the Kew Observatory, 

 that such an instrument might be used for measuring fluctuations of 

 atmospheric temperature ; and the following use afterwards occurred 

 to the author. Were it required to exactly estimate the radiating 



