TRANSACTIONS OF THE SECTIONS. 17 
under ee conditions—temperature of liquid=20°17 C., temperature-difference 
=10°C. 
Specific resistance. 
for water ............ 1:0 ¥f 
» glycerine.......... 3°8 
Pye MLCOHOlis. ie oes ot 9:08 
y amylic alcohol...... 10:2 
» lodideofamyl...... 13°27 
The column of specific resistance is obtained by dividing the resistances of the 
other liquids by that of water. Of all liquids, with the exception of mercury, water 
has the least resistance. Of bodies belonging to the same series, those have the 
greatest specific resistance which have the greatest molecular complexity. 
Experiments were made to determine the rate at which heat of different tempe- 
ratures travelled through water. Through 3 millimetres of water the first effect of 
the heat was manifested 
rl 
in 11 when the temperature-difference was 5:8 
9 ” ” ” 15°8 
7-6 i os i 25°8 
It appeared from numerous experiments made in this direction that for the above 
thickness of water the time for the production of the first effect is diminished 
about 1” for every increase of 5° C. in the temperature-difference. 
With regard to the time required for the heat to penetrate different thicknesses 
of water, it was found that the time increases more rapidly than the thickness. 
‘Thus for a temperature-difference of 10° C. 
millim. * 
For thickness 1 the time required was 3-4 
” ” 3 ” ” 10:4 
91- 
” ” ° ” ” 21:0 
The quantities of heat passing through various thicknesses of water in a given 
time were also determined; and it was found that the resistance was not by any 
means proportional to the thickness. Thus if the resistance through 
millims. 
25 be represented by the number 63:07, 
then 4°5 is He i » 86:24, 
and 6'5 ,, a i » 102-33. 
On examining aqueous saline solutions, it was found that their resistances were 
always greater than that of water, even when the metal in solution was a good 
conductor, and when the solutions were saturated. From the experiments made 
in this direction, it is concluded that the solution of a salt in water affects the re- 
sistance of the latter only either by displacing some of it and altering its specific 
heat. 
Lieut. 
Certain facts bearing on the Theory of Double Refraction. By A. R. Carron. 
On Actinometry. By Lovis Brne. 
The writer describes a series of experiments which he made for the purpose of 
ascertaining the actinic power of light. He shows that the transmission of acti- 
nism through a transparent medium varies with different intensities of light in such 
a manner that instruments constructed for actinometric purposes by means of a 
transparent medium are practically almost useless. He describes an actinometer 
which he constructed, and which consists of a single rectangular tube, at one end 
of which light for measurement is admitted, and to one side of which sensitive 
1868. 2 
