41 
founded liis conclusions, we cannot but be struck with the 
clearness of perception of truth which enabled him to argue 
correctly from inexact experiments. In the notable case, 
indeed, in which Dalton announces the first instance of com- 
bination in multiple proportion (Manch. Mem., vol. 1, series 
2, page 250) the whole conclusion is based upon an erroneous 
experimental basis. If we repeat the experiment as described 
by Dalton we do not obtain the results he arrived at. Oxy- 
gen cannot as a fact be made to combine with nitric oxide 
in the proportions of one to two by tmerely varying the 
shape of the containing vessel, although Iby other means we 
can now effect these two acts of combination. We see, 
therefore, that Dalton’s conclusions were correct, although 
in this case it a23pears to have been a mere chance that his 
experimental results rendered such a conclusion possible. 
‘^Action of Light on certain Vanadium Compounds,” by 
Mr. James Gibbons. Communicated by Professor H. E. 
Roscoe, F.R.S. 
Potassium divanadate, in combination with organic matter, 
is first rendered green, and ultimately blue, by exposure to 
light, being reduced probably to the state of vanadium 
tetroxide. The salt is not sensitive to light in the absence 
of organic matter. 
Gelatine, mixed with potassium divaiiadate, becomes 
slightly less soluble in warm water after being exposed to 
light; this is apparent by the unexposed portions of the 
film swelling and dissolving more quickly vdren treated 
with water than the exposed parts. 
If a colourless film of dry sodium orthovanadate (MaoVO^), 
free from organic matter, be exposed on glass to the sun for 
several hours, it only acquires a faint brown tint. The film 
kept in the dark, with access of air for some hours, regains 
its normal colourless condition. The salt does not undergo 
any change when exposed to diffused daylight. 
