THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JUNE 1864. 



LXIV. On the Measurement of Heiyhts by the Barometer, and on 

 Atmospheric Refraction, haviny reyard to the Constitution of the 

 Atmosphere, resultiny from Mr. James Glaisher's Observations. 

 By Count Paul de Saint-Robert*. 



IN a former brief paper, published in the Philosophical Maga- 

 zine for February 1864, I pointed out the incompatibility 

 of the barometrical formula, generally used for the computation 

 of heights, with the constitution of the atmosphere as found by 

 Mr. James Glaisher in his balloon-ascents, and showed the 

 modification that it must undergo in order to take into account 

 the conditions of temperature actually observed in ascending 

 into the atmosphere. 



Having since calculated the density of the successive strata of 

 the atmosphere arising out of Mr. Glaisher's results, I have 

 noticed that the density of the air decreases nearly uniformly as 

 the height increases. This law of density being admitted, the 

 determination of altitudes by the barometer and of atmospheric 

 refraction is very much simplified. In fact, to obtain the alti- 

 tude in that case, it suffices to divide the difference of pressure 

 at the lower and upper stations by half the sum of the specific 

 gravities of the air at the same stations; and the trajectory 

 described by a ray of light passing through an atmosphere so 

 constituted is an arc of hyperbola. 



This law of density in the atmosphere was made use of very 

 early by mathematicians in the calculation of atmospheric refrac- 

 tion, on account of the facility that it affords for the integration 

 of the differential equation of refraction, and of the conformity 



* Communicated by the Author. 

 Phil May. S. 4. Vol. 27. No. 184. June 1864. 2 D 



