Physics and Chemistry. 107 
this tension, the rays on whic € principal power of absorption is 
exerted, are gradually extinguished so that each increase of density pro- 
duces a less e case of olefiant gas for instance, by taking a 
one. 
The author studied the radiation of gases by making them pass over 
a sphere of heated metal from which they rose in a column in front of 
one molecule so great and another so feeble a power of producing or 
to produce a great effect. : 
3 like mndivier nitrogen and hydrogen which produce little effect when 
form ammonia. The sam , 
radiating powers of other simple gases and their compounds.— 
Rendus, T. li, p. 364, van OM ori se 
5. A Note on the power of Polarization of American Oil of aie ine ; 
by Dr. F. Manta, (In a letter to the Editor.)—It has oe HN ready 
mentioned by Guibourt and ear goon hema a oul of turpen- 
tine possesses a power of rotation of 18°°6 to the right. : 
east, experiments with commercial spirits of turpentine oe me 
to state, that its power of rotation is far from being constant. ave @x- 
* 
