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POPULAR SCIENCE REVIEW. 
direction to the former will result. Therefore, if equal quan- 
tities of heat fall simultaneously on both sides of the pile, the 
effect produced by the one source will be counterbalanced by 
the equal effect of the other source, and the needle will remain 
at zero. 
Let SS 1 represent a glass tube 2' 9" long and 2*4 inches 
in diameter; the ends of this glass tube closed air-tight by 
plates of rock salt, in order that the tube may be used empty 
or filled with the gas to be examined. By means of air-pump 
A A, through the opened stop-cock S, SS' can be exhausted, 
and the gas to be examined admitted into experimental tube 
S S' through the flexible tube j) n. JSTN is the galvanometer, 
P the thermo-pile, and C a cube filled with hot water. Moving 
carefully screen H by means of a screw, such an amount of 
heat may be allowed to impinge from cube C' against the pile 
P, as to counterbalance the effect produced by the heat passing 
through the exhausted experimental tube SS' and striking 
against the opposite face of the thermo-pile. Now, if a gas 
be admitted through n p, a portion of the heat passing through 
S S' will be absorbed, unequal amounts of heat will fall on 
the two sides of the pile, and the source C will preponderate. 
Accordingly, a deflection in this sense takes place, and the 
degree of deflection indicates the amount of absorption by the 
gas in SS'. The heat is supplied to SS' in the following 
manner. G is a cube with boiling water, or as in most ex- 
periments, a copper hood kept at the constant temperature of 
about 270° C and united by bracing with tube P, eight inches 
long, which in its turn is joined ah- tight to S S'. During the 
experiments, chamber F is kept exhausted, and in order to 
prevent conduction of heat from G to SS', F is surrounded 
by a chamber through which a continual current of cold water 
is passing. 0 0, which is graduated and filled with mercury, 
communicates through cl cl with tube S S' ; it serves to deter- 
mine the tension of the gas to be examined in S S'. Y, B, Z, 
are tubes used in purifying and drying the gases. Pure air, 
oxygen, hydrogen, nitrogen, admitted respectively into S S', 
caused a deflection of the needle of 1°. The total amount of 
heat, passed through the exhausted experimental tube, deflected 
the needle of the galvanometer 71° 5 ; if the amount of heat 
necessary to move the needle from zero to 1° be taken as a 
unit, the above 71° 5 deflection corresponds to 308 units. 
Hence, the absorption exercised by the gases mentioned 
amounts to 0‘33 per cent, of the entire heat presented to them. 
Very striking results were obtained with olefiant gas. Of 360 
units of heat transmitted through the exhausted experimental 
tube, 290, or more than seven- ninths, were absorbed after the 
admission of olefiant gas. This result entirely removes the 
