[ 5o6 ] 



may fee what hygrometrical degree the obrervation fo reduced 

 would exhibit, whether higher, lower, or equal to the other. 



Thus, fuppofing an hygrometer on a mountain, at the tempera- 

 ture of 7"^ Reaumur, to ftand at XCVI, and an hygrometer 

 on a plain, at the temperature of 15° Reaumur, to ftand at LXXX, 

 and it is required to know at which place moft vapour exifis in 

 the air, let us then reduce the hygrometer on the plain to the tem- 

 perature of that on the mountain, and fee at what hygrometrical 

 degree, being fo lowered, it would ftand by finding its diftance 

 from C, and to reduce it to 7", the temperature of the mountain, 

 I muft take away S° of heat, for ij** — 8'' = 7^, and confequent- 

 ly fuperinduce 8" of cold. Now I find by this third table, that 

 an hygrometer at LXXX, let its temperature be what it may, 

 wants but 8*^,151 degrees of cold to bring it to C, therefore, by 

 thus fubftrading eight degrees of cold, I find it will arrive very 

 nearly at C, for it wants only 0,151 of it ; therefore more vapour 

 exifts on the plain than on the mountain, fince the hygrometer on 

 the mountain at the fame temperature marks only XCVI. 



This problem may be refolved more readily by infpedting the 

 firft table ; for there we find that XCVI, at the temperature of 7° 

 of Reaumur, indicate about 7,6 grains of moifture in the cubic 

 foot, and that LXXX, at 15^ Reaumur, indicate 8,045 grains — 



or 



