162 PROCEEDINGS OF THE AMERICAN ACADEMY 



SENSITIVENESS OF PLATES. 



riatcs. Daylight. Gas-light. 



Carbutt Transparency .7 



Allen and liowell 1.3 150 



liicliardson stanclarJ 1.3 10 



Marshall anil Blair 2.7 140 



Blair Ins^lantaneous 3.0 140 



Carbutt Special 4.0 20 



Monroe 4.0 25 



Wratten and Wainwright 4.0 10 



Eastman Special 6.3 30 



Richardson Instantaneous 5.3 20 



Walker Keid and Inglis 11. 600 



Edwards 11. 20 



Monckhoven 10. 120 



Beebe 16. 20 



Cramer 1(3. 120 



It will be noted that the plates most sensitive to gas-light are by no 

 means necessarily the most sensitive to daylight ; in several instances, 

 in fact, the reverse seems to be true. 



It should be said that the above figures cannot be considered final 

 until each plate has been tested separately with its own developer, as 

 this would undoubtedly have some influence on the final result. 



Meanwhile two or three interesting investigations naturally suggest 

 themselves : to determine, for instance, the relative actinism of blue 

 sky, haze, and clouds ; also, the relative exposures proper to give at 

 different hours of the day, at different seasons of the year, and in dif- 

 ferent countries. A somewhat prolonged research would indicate 

 what effect the presence of sun-spots had on solar radiation, — whether 

 it was increased or diminished. 



