278 M. C. Lea—Action of the less refrangible rays of Light, ete. 
been due to a continuing power of the colored light upon an 
original impression caused by light accidentally admitted dur- 
ing the preparation, then the papers must have darkened all 
over by the agency of gallic acid, instead of developing an 
image. So that the system of experiment adopted was in itself 
incidentally a precaution against any such source of error. 
Nevertheless, wishing to obtain a result that would be en- 
romide 
In the foregoing pages, I have briefly given the result of one 
hundred and sixty experiments The results, with such slight 
and altogether unimportant variations as necessarily arise from 
slight differences of preparation and differences in the charac- 
ter of the sun’s light, were remarkably concordant, and may be 
summed up as follows: 
gBrand AglI are sensitive to all the visible rays of 
the spectrum. 
Aglis more sensitive than AgBr to all the less refran- 
2. 
gible rays and also to white li 
gl or AgBr separately. ie 
5. There do not exist any rays with a special exciting or & 
special continuing power, but all the colored rays are capable 
mencing and continuing the impression on silver 
iodide and bromide. 
Philadelphia, March 6, 1875. 
