438 
3-5, which reduced the striking distance to 2. The light 
was greenish, faint, and fluorescence almost insensible. 
“31. Concentrated acetic acid showed nothing worth 
notice; the light was livid, and fluorescence very faint. 
‘¢ 32. A fragment of camphor was fixed by pressure on the 
disc. The light was green, like that of alcohol; when the 
disc was positive, it was covered with intense emerald stars, 
and the mercury with bluish-green light, brighter than the 
rest. This was still brighter at the disc when negative, and 
red sparks flew from it. No fluorescence. 
‘¢33. This was again tried in the air vacuum 0:25, but 
with four double Groves. The light was light green, but the 
stream narrow, and the strata were well defined. Red sparks. 
flew from the negative electrede; quinine drawings were not 
visible outside, but one attached to the inside of the glass was 
seen faintly. This was probably caused by the residual air. 
** It follows from these facts, that though my original con- 
clusion, that the fluorescent rays can be produced only in 
oxygen and nitrogen, is not rigorously true; yet that in this 
respect they very far predominate over the others. It appears 
from (27) that they do not lose this quality in combination ; 
and from (23) that nitrogen is not deprived of it by carbon, 
though it is (28) by hydrogen, which seems eminently anti- 
fluorescent. It, sulphur, and carbon, seem entirely to destroy 
this power in oxygen; and probably the case is the same with 
all other highly electro-positive substances. Equally deserving 
of notice is the power of developing green light which seems 
to belong to the compounds of carbon. There remains a wide 
field for inquiry on these points, especially with respect to the 
various ethers and bodies of the same family, and also to the 
remaining electro-negatives, on which I hope soon to enter, 
with the advantage of having in some degree ascertained the 
difficulties which are to be encountered.” 
