SCIENTIFIC SUMMARY. 
343 
Photographic artists," 284 ; apparatus makers, 38 ; album makers, 38 ; 
chemists, 17 ; moimters, 6 ; paper makers, 15 ; publishers, 16 ; dealers in 
materials, 28. 
New Photo-Engraving Process. — The Chemical News asserts that a new 
process of photo-engraving by M. Baldus is about to be introduced, far 
surpassing in simplicity, certainty, and beauty of result, the best works 
produced by Messrs. Woodbury, Swan, and others, and at a price fabu- 
lously low. The process is a secret one but is said to be exceedingly 
simple. 
Long-kept Plates. — At a meeting of the Philadelphia Photographic Society 
a member exhibited a print from a tannin negative which had been kept 
five years previous to exposure, and a tannin negative developed one year 
after exposure. 
The Nature of the Latent Image. — Mr. Carey Lea has advanced what he 
considers “ some entirely new views,” on the nature of the latent image : he 
says : “When light considered in reference to its illuminating power falls upon 
any surface, we are accustomed to regard the effect of that illumination as 
passing away at the same instant of time that the illumination terminates. 
But there are a vast number of well recognised exceptions to this rule which 
we know under the name of phosphorescence and fluorescence,” which proves, 
says Mr. Lea, “ that bodies may by light be thrown into a state of vibratory 
motion, lasting for a longer or shorter, sometimes for a very considerable 
time after the exciting cause is removed, and that, so long as this vibratory 
movement continues they will themselves emit light.” The writer then 
proceeds to argue that there is no reason to doubt the property we con- 
veniently call actinism may have similar power on certain bodies and that the 
latent image “ is simply a phosphorescence of actinic rays. . . Pure iodide 
of silver undergoes no decomposition by light when thoroughly isolated from 
all substances, organic and inorganic, which are capable of aiding in effecting 
a reduction. But, if exposed to light, it continues for a certain time there- 
after to retain the vibrations it received ; and just for so long as these vibra- 
tions continue will it be instantly decomposed if brought into contact with any 
substance which would have caused its decomposition had the two been subjected 
to the action of light together. . . For this property of light I propose the 
name of * Actinescence.’ The more we examine these phenomena the 
more we shall perceive that actinescence must, so to speak, exist j for different 
phosphorescent bodies emit light of very different colours, showing that their 
respective capacities of prolonged impression are confined to rays of a certain 
refrangibility, differing from each other in each case. Now we know that 
the actinic influence accompanies rays of a certain refrangibility, especially 
the violet, the indigo, and the rays immediately beyond the visible. The 
permanence therefore of these actinic rays, under suitable circumstances is 
no more difficult of conception than that of other rays, a fact which has 
been known and recognised for centuries.” Mr. Lea then argues that the 
faculty of receiving a latent developable impression depends on the posses- 
sion of two properties, viz. sensitiveness to light, and actinescence ; that a body 
may be actinescent without being sensitive to light, and therefore unable to 
retain the latent image, and that on the other hand substances may be 
merely sensitive to light when brought in contact with others, but which 
not retaining the impressions made by light until the decomposing agent be 
