136 MALUS. 
which our friend alleges, the instance of the light which _ 
is engendered in a vacuum, by the aid of the voltaic 
current, passed through simple substances, such as car- 
bon, platinum, &c. 
In the second part of the memoir Malus seeks to 
establish that the different natures of various lights only 
differ from each other in the greater or less proportion 
of caloric which they contain. The red light would 
thus be the most heating, the violet the least so, which 
agrees with experiment. According to a singular opinion 
professed by the author, all rays, if possessing a certain 
high intensity, ought to produce the sensation of white- 
ness.* 
The third part of the work is devoted to mechanical 
consequences which result by analysis from the supposi- 
tions explained in the first two sections. It may suffice 
to say, that the author finds, like all the partisans of the 
system of emission, that the velocity of light ought to be 
greater in water than in air: every one therefore will see 
how superfluous it would be now to go into a discussion 
of the details of such a subject. 
* The “singular’’ opinion here ascribed to Malus is perhaps not 
altogether without foundation, at least in some cases. It is certain 
that while the prismatic spectrum of the white light of the clouds 
present a clear yellow and green portion, that same portion, when the 
direct rays of the sun are substituted, appears to the eye intensely 
brilliant and white. And it is far from certain that in some other ex- 
periments, which have been the occasion of some little controversy 
and where the colour of certain parts of the spectrnm has appeared 
to undergo a change, the intensity of the light reaching the eye may 
not beconcerned. In fact, the sensation of colour is one so entirely de- 
pendent on unknown physiological causes, that we can hardly venture 
to predict what the result may be on different individual eyes, though 
all the optical conditions may be precisely the same. It may not be 
altogether without a bearing on this subject, to remark the extremely 
contradictory statements made by different observers as to the colour 
of intensely brilliant meteors.— Translator. 
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ae ee eres 
