THE PHOTOMETER. 



55 



COMPARISON OF SHADOWS. 



would be nearly four times as great as that from the can- 

 dle. Of course, by exactly measuring the two distances 

 and squaring the numbers expressing them, the exact ratio 

 would be ascertained. 



It would be found, in using this instrument, that if, in- 

 stead of a lamp at A, candles of the same kind as the one 

 at B are used, and if the distance of A from the bar m, 

 which intercepts the light, is made double that of B, there 

 must be four candles at A to make the shadows equal. 



LAW VEBIFIED. 



There have been various other methods devised of meas- 

 uring the comparative intensity of light. One more I will 

 describe. 



