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L. On the Laws of the Expansion of the Transparent Liquids by 

 Increase of Temperature. By Professor Potter, A.M.* 



IN my paper " On the Definition of the Temperature of Bodies, 

 and on its Measurement by Thermometers," published in 

 this Magazine, vol. xxiv. p. 447, I showed that the expansion 

 of mercury, as determined by the experiments of MM. Dulong 

 and Petit, accorded very nearly to the law of uniform expan- 

 sion, or if V were the volume at any temperature, V the 

 volume at t° above it, a a constant depending on the magnitude 

 of the degrees on the thermometric scale employed, and e the 

 base of the hyperbolic logarithms, then 



V=V .€«<°; 



and for the natural unit of temperature, taken to be the interval 

 of sensible heat between the freezing- and boiling-points of water 

 under ordinary circumstances, the value of a was 



a= -0178576. 



The determinations of M. Regnault for the expansion of 

 mercury are found to be also according to the law of uniform 

 expansion very accurately, but with the value of a as follows : — 



a = -0179901, 



The differences between the calculated quantities and those 

 given by M. Regnault for a volume unity at the freezing-point 

 of water commence only at the fourth place of decimals. With 

 our thermometric scales still unsettled, it is useless to expect 

 greater accordance. 



On examining the valuable results of M. Ch. Drion and M. 

 J. Is. Pierre, given in the Annates de Chimie et de Physique, 

 on the expansion of many transparent liquids by increase of 

 temperature, it will be found that few, if any of them, are sub- 

 ject to the law of uniform expansion. 



When many years ago I was engaged in experiments on 

 photometry, I found that the quantity of light reflected out of a 

 given incident pencil of rays, at the surfaces of crown, plate, 

 and flint glass, was a hyperbolic function of the angle of inci- 

 dence. The results were first published in vol. iv. (for 1831) of 

 Brewster's ' Edinburgh Journal of Science' ; and the formula?, 

 with the values of the constants for the three kinds of glass 

 used, are also published in my ' Treatise on Physical Optics/ 

 vol. ii., " 0* the Corpuscular Theory of Light," p. 36. 



Finding that the results of M. Drion for the apparent volumes 

 of hydrochloric ether at temperatures from 0° C. to 133° C, 

 approaching its point of entire vaporization, were very far from 



* Communicated by the Author. 

 2 A2 



