SCIENTIFIC SUMMAKY. 
481 
removes the one atom to a greater distance from the other, at the moment 
of farthest departure from the point of rest ; while such an increase of 
distance must produce a corresponding momentary weakness in the attrac- 
tion by which the two atoms are held together, so rendering more easy their 
permanent separation. The tendency to separation would also be increased 
by a lowering of the rate of vibration simultaneously with the increase of 
amplitude, because it would prolong the moment of weakest attraction. It 
is obvious that no augmentation in the amplitude of those ordinary vibra- 
tions of the molecules of a compound body which are incident to its 
temperature could produce the same effect ; because the atoms of each 
molecule are not in this manner made to vary their distance one from an- 
other. ... In order that the vibrations between the atoms constituting 
a compound molecule may have their motion amplified by those of the 
lumineferous ether, it is not necessary that the latter should be exactly 
synchronous with the natural rate at which the atoms tend to vibrate, 
although the more nearly they are synchronous the more effective they will 
be. Where we have 800 billions of vibrations in a second, a few millions 
more or less can be of little importance.” Mr. Ponton concludes that the 
action of light in fluorescence, is quite different from what it is in photo- 
graphy. u In fluorescence, the molecules, or their constituent atoms, on 
taking up the motion from the ethereal waves, change its rate. The incident 
light is absorbed and a new set of ethereal waves is propagated by the vibrat- 
ing atoms or molecules, and these new waves have a rate of vibration 
slower than that of the incident waves ; hence the colour corresponds to 
these more leisurely vibrations ; hence, also, incident ethereal waves too 
rapid in their rate of vibration to affect the optic nerve, may stimulate the 
molecules or atoms to propagate waves of that slower rate of vibration 
which is capable of exciting the nerve into action. The waves whose 
vibrations are thus appropriated and lowered in their rate by the fluorescent 
body, are those most active in photography ; and hence fluorescent surfaces 
are photographically inert, the waves which they propagate being of too 
slow a period to be effective in this manner. The continuance of the 
vibratory action, after the exciting light has been removed, is similar to 
phosphorescence. Every motion once begun has a tendency to continue 
till checked by some retarding force. It is, therefore, not at all wonderful 
that the vibrations between the constituent atoms of the molecules of the 
sensitive substance should continue for a considerable time after being re- 
moved from the excitement of the light. The phenomenon is of the same 
nature as the retention of its heat by a body for a considerable time after it 
has been taken out of the fire.” * At an earlier stage of the controversy, 
other views were advanced, but we have not space for further particulars. 
Awards of Photographic Jurors at the Paris Exhibition. — We give a list 
of the English photographers who have carried off honours at the Paris 
* E. C., writing in the British Journal of Photography , in reply to the 
above statement, asks : u How is it, then, that dry plates have been 
developed several years after exposure, and commonly months' afterwards, 
without more than ordinary difficulty P It is evident that in the film the 
c excitement ’ must still be kept up without appreciable diminution .” 
