444 Prof. TyndalPs Contributions to Molecular Physics. 



liquid destroys the previous equilibrium, the galvanometer needle 

 moves, and finally assumes a steady deflection ; and from this 

 deflection we can immediately calculate the quantity of heat ab- 

 sorbed by the liquid, and express it in hundredths of the entire 

 radiation. 



For example, the empty cell being placed upon its stand, and 

 the needle being at 0°, the introduction of iodide of methyle 

 into the cell produced a deflection of 30 o, 8. The total radiation 

 on this occasion was 44°-2. Taking the force necessary to move 

 the needle from 0° to 1° as our unit, the deflection 30 o, 8 corre- 

 sponds to 32 such units, while the deflection 44 0, 2 corresponds 

 to 58*3 such units. Hence the statement 

 58-3:100 = 32:54-9, 

 which gives an absorption of 54*9 per cent, for a layer of liquid 

 iodide of methyle 0*07 of an inch in thickness. 



§ II. Absorption of radiant heat of a certain quality by eleven 

 different liquids at five different thicknesses. 



The following Table contains the results obtained in this 

 manner with the respective liquids there mentioned. It em- 

 braces both the deflection produced by the introduction of the 

 liquid, and the quantity per cent, intercepted of the entire radia- 

 tion. It has been intimated to me by some of my continental 

 friends that the publication of such details as would enable a 

 reader to judge of the precision attainable by my apparatus would 

 be desirable. In this paper I shall, to some extent, endeavour 

 to satisfy this desire, making use, however, of my ordinary ex- 

 periments. 



Table I. — Radiation of heat through Liquids. Source of heat, 

 red-hot platinum spiral. Thickness of liquid layer 0-07 of 

 an inch. 



Name of liquid. Deflection. Absorption per 100. 



Iodide of methyle . . 30*8 54-9 



Iodide of ethyle . . . 33-0 60-4 



Benzole 35-3 670 



Amylene 37*7 74-8 



Sulphuric ether . . . 39-0 79-4 



Acetic ether .... 39'6 81-6 



Alcohol 41-0 86-6 



Water* 43-3 91*4 



Total heat ..... 44-2 100 



* To prevent the water from attacking the cell, it was always first satu- 

 rated with the substance of the cell itself, namely, transparent rock-salt. 



