SENSITIVENESS OF PLATES.
Plates. Daylight. Gaslight.
Carbutt transparency 0.7 ..
Allen and Rowell 1.3 150
Richardson standard 1.3 10
Marshall and Blair 2.7 140
Blair instantaneous 3.0 140
Carbutt special 4.0 20
Monroe 4.0 25
Wratten and Wainwright 4.0 10
Eastman special 5.3 30
Richardson instantaneous 5.3 20
Walker Reid and Inglis 11.0 600
Edwards 11.0 20
Monckhoven 16.0 120
Beebe 16.0 20
Cramer 16.0 120
It will be noted that the plates most sensitive to gaslight 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 different countries. A somewhat prolonged research would indicate what effect the presence of sunspots had on solar radiation—whether it was increased or diminished.
From the Proceedings of the Academy of Arts and Sciences.—Amer. Jour.