480 
POPULAR SCIENCE REVIEW. 
•with a pale blue flame giving a feeble light. A jet of g as, obtained by the 
action of nitric acid on copper, being allowed to play through this burning 
vapour, the result is a very brilliant actinic light, which can be kept up for 
a considerable time with a very small amount of trouble. It must be 
remembered, in using this light, that the burning bisulphide of carbon gives 
off fumes of sulphurous acid. 
The Nature of the Latent Image. — In our last we gave what were called 
11 some entirely new views” on this subject, as advanced by an American, 
Mr. Carey Lea. This gentleman has since been very active in promulgating 
his theory; and although it has been very clearly shown in the English 
j oumals to which he contributes that, as we suspected (see note page 344), 
he has no claim to be regarded as the originator of such views, still, in the 
American journals, he continues to assume the position of one who first com- 
municated them to the public, and to strangely exaggerate their importance. 
Air. W. H. Harrison laid claim to having first published the ideas Air. Lea 
pertinaciously claims as his own, and a controversy ensued, in which the 
latter gentleman strove to show that Mr. Harrison’s views entirely differed 
from his own, and that they were false, basing his argument upon the 
assumption that Air. Harrison held the action of light to be simply an 
augmentation of the amplitude of the ordinary vibrations of molecules com- 
posing the sensitive surface — an assumption not warranted by Air. Harrison’s 
remarks. At an early stage of the controversy, Air. Harrison gracefully 
withdrew his claims to priority of publication in favour of Air. Alungo 
Ponton, F.R.S.E., who, in reply to Air. Lea, says * u The vibrations which 
we (himself and Air. Harrison) suppose to be effected by the light, are not 
the ordinary vibrations between molecule and molecule of the sensitive 
compound incident to its temperature ; but a totally distinct set of very 
minute vibrations established between atom and atom of the constituent of 
each molecule 'of the substance. Whether such minute vibrations exist at all 
before exposure to the light, is unimportant ; but it is evident that the greater 
the motive energy of the light brought to bear upon them, the greater will 
be the amplitude of those vibrations ; consequently the greater will be the 
facility for effecting a separation between the atoms. The rate of vibration 
is a different affair, and will depend on the nature of the constituent atoms, 
and the strength of the chemical attraction by which they are held together. 
The more nearly the natural rate at which these atoms tend to vibrate 
approaches to the rate of the violent waves, the more readily will they take 
up the motion from those waves and have their amplitude thereby enlarged. 
But their rate will not be altered by the energy which they absorb from the 
ethereal waves ; while, even if it were quickened, such acceleration of the 
rate could not produce any increased tendency to decomposition. An increase 
of motive energy can affect a vibration in only one of two ways : it must 
either quicken its rate, or enlarge its amplitude. Now the doubling or even 
the trebling of the rate of vibration between two heterogeneous atoms 
constituting a compound molecule, could have no effect in promoting their 
permanent^separation : but every increase in the amplitude of the vibration 
In the British Journal of Photography. 
