OP ARTS AND SCIENCES. 



427 



it can be proved that such a relation exists between the relative moist- 

 ure of the ujjper atmosphere and the light of the sky, it is evident that 

 we have here a hydrometer with a widely extended range. 



A curve has been constructed for each series of observations, having 

 intensities as ordinates and natural sines of the sun's angular distances 

 as abscissas ; and an inspection of these curves shows a close agree- 

 ment in their forms, which indicates that, notwithstanding the great 

 differences in the intensity of the light, its variations followed the same, 

 or nearly the same law, in each case. Other curves were constructed, 

 with co-ordinates equal to the logarithms of the co-ordinates of the 

 curves just mentioned, which show by their approximation to straight 

 lines that the law of the variation of the light may be expressed by 



