.Amount of Light by the Precipitation of Gold. 

 No. IV.— October 13, 1858. 



93 



Nos. III. and IV. represent days nearly alike in temperature 

 and cloudy condition, and they also show a similar amount of 

 chemical power in the light of each ; but when compai'ed with 

 I. and II., we find the efi"ect of the cloudy condition of the sky 

 in the decreased amount of gold precipitated. 



Nos. V. and VI. represent extremes, the first being a clear 

 warm day, while the latter was cold, very cloudy, and dark; 

 accordingly we find the difiuse light of the clear warm day had 

 eight times as much chemical power as that of the colder and 

 darker day. 



These experiments serve to demonstrate the capabilities of 

 this process, and may perhaps recommend a trial of its merits 

 to such as are interested in photometric pursuits ; and by the 

 use of the same quantities of a similar solution, exposed in a like 

 manner in various countries, valuable tables might be con- 

 structed. 



