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saad ning OI 
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and on the refractive Powers of different Gases. 297 
drogen predominates, weakest where carbon prevails, and 
still weaker where oxygen abounds. Thus etuer refracts 
more than alcohol ; and the essence of turpentine more than 
the fixed oils: carburetted hydrogen refracts less than pure 
hydrogen, and so much the Jess as the proportion of car- 
bon is increased in it. These views, which by themselves 
furnish but a very slight induction, assume some importance 
when they agree with the results obtained by a rigorous cal- 
culation. 
But the diamond here presents a very great exception, 
The experiments. of Newton give as its reftadtive power 
= 3°2119, that of the air bene 1; this amount is almost 
double of that just now assigned to carbon. Condensation to 
the solid state will not explain so great a difference; for in 
gum, for instance, which ‘is also a solid, we do not see that 
this circumstance has an influence equally disproportioned : 
wax, which is equally solid; ought to refract much more 
than oil of turpentine, for it contains also more carbon ; ne- 
vertheless it refracts much less, and far less, for a stronger 
reason, than the diamond. 
«© What ought we to conclude,” say the authors, “ from 
~ the detail we have given? Is not the diamond a pure car- 
bonate? and does not its great refractive power display the 
presence of hydrogen, the most energetic of all other’ mnie 
in the power of refraction?” 
It would be necessary, according to the experiments of 
Newton, that the diamond should contain more than a third 
of its weight of hydrogen, in order to explain, by the 
presence of this ingredient, its great refractive power. If 
we want to reduce this number prépobtionally to the small 
differences remarked between the calculation and the theory, 
we should carry it to one-fourth, but we cannot descend 
lower without being in opposition to all the other re- 
sults, 
The authors, on this occasion, request the first class of 
the Institute to repeat, by a direct experiment, the analysis 
of the diamond with all the precaution which should attend 
their suspicions of the presence of hydrogen. We know 
that 
