214 



Professor Roscoe, 



[March 2, 



That these calculated results agree very closely with the experi- 

 mental data, — with the observed action, — is seen by comparing the 

 numbers in Table, No. II., expressing the observed and calculated 

 action. 



Table II. 



The amount of Chemical Action effected at a point upon the Earth's 

 Surface on any cloudless day, by the direct Solar Rays, depends 

 alone upon the Sun's zenith distance ; or upon the height of the 

 column of air through which the Rays have to pass. 



Knowing the law which regulates the absorption of the chemical 

 rays, we can calculate what the action would be if there were no atmo- 

 sphere to diminish the power of the rays. It is thus found that if the 

 sun's rays were not thus weakened, by passage through the atmosphere, 

 they would produce an illumination represented by 318 degrees of 

 light : or they would effect a combination in one minute, upon an un- 

 limited atmosphere of chlorine and hydrogen on which they fell per- 

 pendicularly, of a column of hydrochloric acid, 35 • 3 metres in height. 

 The sun's rays having passed perpendicularly through our atmosphere 

 to the sea's level, effect an action of only 14*4 light metres ; or nearly 

 two-thirds of their chemical activity has been lost by extinction and 

 dispersion in the atmosphere. 



A large number of most interesting conclusions may be drawn from 

 the facts already noticed. Thus, for instance, we may determine the 

 chemical action which the solar rays will produce on the various 

 planets ; for we know that the intensity of the chemical illumination 

 varies inversely as the square of the distance of the planet from the 

 sun. The numbers in Table III., express this chemical action in 

 degrees of light, and in heights of columns of hydrochloric acid called 



