Count Paul de Saint-Robert on Atmospheric Refraction, 423 



p , p densities of the air mixed with aqueous vapour at the same 

 respective stations. 



vr , w pressures of the vapour contained in the atmosphere at 

 the same stations. 



t , t absolute temperatures at the same stations, the absolute 

 zero being 274° C., or 493°*2 F. below the melting-point 

 of ice. 



g gravity at lower station. At 45° of latitude and at the sea- 

 level G = 9 m *80604 = 32*172 feet (Bessel). 



r , r distances of the stations from the earth's centre. 



Example. Measurement of Monviso, August 12th, 2 h 30 m p.m. 

 1863, taking Verzuolo (425 metres) as the lower station : — 



Verzuolo. Monviso. 



Barometer reduced to the \ 

 freezing-point . . J 



Thermometer in open air . . . 27°*15 C. 6° C. 



Thermometer with wet bulb . . 21°*3 6°* 



Therefore 



^ =0 m -7239 p =0 m *4836 



t =301°-15 t =280° C. 



CTo =O m -01535 sr =0 m 007 



Monviso above Verzuolo # = 341 7*3 metres. 

 Verzuolo above the sea . 425*0 „ 



Monviso above the sea . 3842*3 " 



Taking into account the diminution of gravity in receding 

 from the centre of the earth, the difference of level between 

 Monviso and Verzuolo comes out 3426*7 metres, and the alti- 

 tude of that peak above the sea 3851*7 metres. 



Delcros's barometrical Tables, founded on Laplace's formula, 

 give 3860*7 metres. It must be remarked that, if this result is 

 only 9 metres in excess of that deduced from my formula, that 

 is due to the use of the coefficient 18336 therewith made, in 

 place of 18405, resulting from the more accurate determination 

 of the relative weight of the air and mercury by M. Regnault, 

 which should be used, and which would bring the difference to 

 22 metres. 



Geodetical Formula. 



x = 2r C sin -sin 



! sin ( v ~d 



r — r —x-\ , 



r -x 



* The temperature of the thermometer with wet bulb was not observed 

 on the top of Monviso ; but as we were in the mist, the difference of wet and 

 dry bulb must have been very small. 



