74 M. C. Lea on a Theory of Photo-chemistry. 
as in most light-phenomena that pass under our notice, where 
the return to photo-equilibrium is immediate, but this equilib- 
rium is only reached after the interval of hours or days. 
Consequently, so long as these vibrations of non-luminous 
normal influences. And if a film of such material has had parts _ 
exposed to light while other parts have been protected, and the 
whole be then exposed to influences provocative of decomposi- 
tion, it is evident that those influences may be so graduated that 
they will tell o- the parts predisposed by the impression _ 
e 
they have received. 
istence of, may be conveniently termed Actinescence. i 
That this word does not express with entire accuracy what is 
This function of light which I here endeavor to prove the ex: 
: 4 
intended to be conveyed, is sufficiently evident. But it has the 
advantage of connecting the phenomena with the parallel one 
of phosphorescence, and is perhaps on the whole as well sui 
as any other that could be found or made. 
Where, through phosphorescence, a body temporarily retains, | 
and subsequently emits light, that emission, in the gradual re 
turn to its photo-equilibrium, is rendered evident by the phe 
nomena that usually accompany the emission of light. Sur- 
rounding objects are illuminated, faintly but visibly. Should 
we not therefore expect similar results in the case of actines- 
cence? 
nce ray 
_ Not only should we find them, but they have actually been 
‘ibed, though not understood. For in actinescence we have 
explanation of the phenomena described by Niepce de St. 
Victor as the “storing up of light” (emmagasinement de la lu- 
miére). St. Victor showed that certain objects exposed to light 
and then carried into darkness had in some cases pon the 
which | 
power of acting chemically upon other bodies with , 
were placed in contact. His results were received at first 
something like derision, and the facts, which could not be denied, 
ision, an 
were said to arise from some chemical decomposition which had 
taken place in the body during its exposure to light, generat- 
ing reducing agents which were subsequently given off in the : | 
darkness. 
But until now, the identity between the latent physical mies = 
and the storing up of light has not even been guessed at, 
less the perfect parallelism between these phenomena and that 
of phosphorescence. That a body may immediately regain its 
equilibrium with respect to one sort of rays and slowly with 
respect to another, involves no difficulty cada 
ually see this in the facts of nmo L p hospno rescen 
. 
—_ 
we contiD- i 
