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.” 
