Chenistry and Physics. 407 
em. dis- 
tance, and exposed to-the light coming from the brightest part of 
Sas pao As the numbers would be very large, however, if 
the chloride were taken as a unit, it was thought better to give 
them in even hundred thousands. 
SENSITIVENESS OF PLATES. 
Plates. Daylight. Gas-light. 
Carbutt Transparency .....--..---- 7 
Allen and Rowell V3 150 
Richardson standard 1°3 10 
Marshall and Blair aT 140 
Blair Instantaneous. < ic ss cans uucu 3°0 140 
Uarbukt Seetiahi ck o.au Kons cwnous 40 20 
OG sh oh ee ane See 4°0 25 
Wratten and Wainwright..-....--. 40 10 
Eastman Special 5:3 30 
Richardson Instantaneous.-..-..-- 5'3 
Walker Reid and Inglis _...--.---- 1° 600 
Edwards je ty 20 
Monckhoven 16° 120 
Sy peepee se FO 16° 20 
Cramer. __. 16° 120 
Tt will be noted that the plates most sensitive to gas-light are 
by no means necessarily the most sensitive to daylight; in sev- 
eral 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 
fina] result. 
Meanwhile two or three interesting investigations naturally 
Suggest themselves: to determine, for instance, ed relati 
a 
