measuring the comparative Intensities of Light, 87 
In this experiment, as the candles burnt with equal bright- 
ness, it is evident that the intensities of their united and single 
lights were as 2 to 1, and in that proportion ought, according 
to the assumed theory, the squares of the distances, 60,8 and 
43,4 to be ; and in fact, 60,8“ = 3696,64 is to 43,4 = 1883,56 
as 2 is to 1 very nearly. . 
Again, in another experiment, (No. 2.) the distances were, 
with two candles = 54 inches. Square = 2916. 
with one candle = 38,6. - = 1489,96 
Upon another trial (experiment No. 3.) 
with two candles = 54,6 inches. Square = 2981,16 
with one candle = 39,7. - = 1576,09 
And in the 4th experiment 
with two candles = 58,4 inches. Square = 3410,56 
with one candle = 42,2. - = 1780,84 
And taking the mean of the results of these four experi- 
ments. 
Squares of the distances. 
With two candles. With one candle. 
In the experiment No. 1, 3696,64 - 1883,56 
No. 2, 2916 - 1489,96 
No. 3, 2981,16 - 1576,09 
No. 4, 3410,56 - 1780,84 
4) i3 00 4’3 6 “ 4) 6736,45, 
Means 3251,09 and 1682,61, 
which again are very nearly as 2 to 1. 
With regard to these experiments it may be observed, that 
were the resistance of the air to light, or the diminution of the 
light from the imperfect transparency of air, sensible within 
