RADIANT HEAT, AND ITS CONVERSION THEREBY INTO SOUND. 
321 
Bisulphide of Carbon 
Chloroform. 
Benzol. 
Iodide of Methyl . 
Iodide of Ethyl . . 
Amylene. 
Sulphuric Ether . . . 
Acetic Ether . 
Formic Ether . . . 
Alcohol. 
A barely sensible action. 
No action. 
No action. 
No action. 
No action. 
No action. 
A barely sensible action. 
No action. 
No action. 
No action. 
The minute deflections produced by bisulphide of carbon and sulphuric ether had 
nothing to do with liquid films, so that the words c f no action ” might have been 
written against these substances as against the others. While therefore recognising 
the fact of condensation, these simple experiments prove how incorrect it is to credit 
the condensed films with the effects which have been ascribed to them. According to 
Magnus, alcohol exhibits a force of vapour-hesion particularly strong: but we here see 
that even this vapour produces no sensible effect. The vapours have been tested with 
other sources of heat, with the same result. 
The deportment of dry and humid air is, as usual, very instructive. When the thin 
plate of rocksalt resting on the naked face of the pile, was exposed to the common 
air of the laboratory, it, of course, contracted a film corresponding to the humidity 
of the air. The sweeping away of this film by dry air produced a very small deflec¬ 
tion indicating cold. When, on the contrary, humid air was urged against the salt, 
the deflection indicating heat was prompt and large. We have now to test the 
action of the liquid film thus formed upon radiant heat. The circular plate of rock- 
salt before referred to was mounted, with the incandescent spiral on one side and the 
pile on the other. The slit was so arranged that dry and humid air could be sent in 
succession over the surface of the plate. As before, the radiation from the spiral was 
neutralised by the compensating cube, the needle pointing to zero when the two sources 
were in equilibrium. On sweeping dry air over the plate of salt, so as to remove the 
film contracted from the laboratory air, there was no motion of the needle. On pouring 
humid air from the slit over the salt, there was no motion of the needle. To moisten 
the air it was urged from bottom to top through a tall jar filled with wet bibulous 
paper. The same apparatus had furnished humid air which produced a swing of 80° 
when urged against the thin plate of rocksalt resting on the face of the pile. As a 
barrier to radiant heat it was nevertheless powerless. The condensation may even be 
considerably enhanced without producing any sensible effect. Through a glass tube 
I urged my breath against the plate of salt so as to produce the colours of thin plates, 
without any sensible effect upon the galvanometer. 
Having thus clearly shown what films, even in an exaggerated form, cannot 
MDCCCLXXXII. 2 T 
