508 Scientific Intelligence. 
within a milligram. If a burner with an opening of known diam- 
eter be used, and the estimation be made, as is now common with 
the standard candle, by noting the height of the flame, and the 
number of the divisions the key is turned, the character of the 
flame and the consumption of material may be absolutely con- 
trolled and registered. The author suggests the use of this appa- 
ratus for determining vapor tensions, especially of the more dan- 
gerous burning oils.— Ber. Berl. Chem. Ges., vii, 103, Feb., 1874. 
si ae 
3. On the so-called Continuing Rays of Becquerel.—In 1848, 
Becquerel stated that, if silver chloride be exposed to the spec- 
trum directly, it begins to be blackened first in the outer violet 
rays, the action subsequently extending up to the line F. But if, 
previous to this exposure, diffused light be allowed to fall upon it 
long enough to permit a very feeble action to take place, then, 
when exposed to the spectrum, not only does the blackening take 
place in the outer violet, but throughout the whole spectrum even 
to the outer red. He hence called the violet the exciting rays, 
and the others continuing rays, because they appeared to continue 
the action when it was once commenced by the violet. These ex- 
plates in the camera, and then to give them a supplementary 
exposure behind red glass (or any glass which transmits no blue 
i ion with Zencker and P 
o 
ed to the violet argentous chloride (Ag,Cl); 2d, that this 
violet chloride, as proved by the experiments of Seebeck, Herschel, 
Poitevin, Zencker, and others, is sensitive for almost all the colors 
of the spectrum ; a fact of great significance in color photography. 
Becquerel therefore obtained an effect from all parts of the spec- 
trum because he used this violet chloride, produced by his pre- 
liminary exposure. In proof of this, the violet chloride produced 
aes : ry exposure can re- 
sult in so intense a darkenin Vogel thus explains: Ist, the violet 
is reduced to me silver by the light : 
o 
a 
= 
5. 
e 
H 
o 
2B 
oe 
5 
ig 
<} 
2, 
3, 
8 
Fe 
(a2) 
