658 FEEDEEICK GTJTHEIE ON THE THEEMAL EESISTANCE OF LIQUIDS. 
heat well, and is consequently highly athermanous, forms on that very account an 
abundant source of heat to bodies in contact with it. And if the heat move through 
the liquid, by way of conduction, with facility, the quantity of heat which the heated 
liquid gives up in a given time to another body in contact with it, is great — that is, the 
resistance of the liquid is found to be small. 
§ 70. Though more or less heat passes instantly through a partly athermanous liquid, 
yet some is absorbed, and the amount absorbed, and therefore the degree of athermancy, 
is not independent of the specific heat of the liquid ; for the transmitted heat is mea- 
sured before the liquid has become a secondary source of radiant heat in virtue of the 
heat which it has arrested. It is found, indeed, that the order of absorption in the case 
of water, alcohol, and bisulphide of carbon is the same as that of the specific heats of 
the same liquids. 
§ 71. With contact heat the case is different; for when a liquid has a high specific 
heat, although the rise of temperature will be small when the heat enters it, yet this 
small increment of temperature corresponds to a large absolute accession of heat ; so 
that when, as in my experiments, the liquid becomes a source of heat the absolute 
quantity of heat given out is also great; hence the specific heat of the liquid in 
these contact experiments is of no influence. Accordingly we need not look to the 
different nature of the heat employed to reconcile my experiments with those of 
Dr. Tyndall. 
§ 72. Concerning the relation between thermal and electrical resistances, a few remarks 
may be allowed. It has been shown in §§ 46 seq., §§ 52 seq., that the hotter a liqiud 
(water) is, the less is its resistance, both as measured by the time t required for the first 
penetration, and by the quantity of heat arrested in a given time-lapse. This is in 
accordance with the observations of Wiedemann, who found that the resistance of a 
solution of sulphate of copper diminished more than one half when its temperature was 
raised 55° C., and with the general law of liquids that the resistance diminishes as the 
temperature increases. With metals, as has been long known, the electrical resistance 
increases with the temperature. If, therefore, in the case of electricity the law con- 
necting resistance with temperature is the reverse with liquids to what it is with solids, 
it may well be so with heat ; so that while hot solids may conduct heat worse than cold 
ones, a hotter liquid may conduct heat better than a colder one. 
§ 73. The experiments § 61 were especially made to determine whether the addition 
of sulphuric acid, which so greatly diminishes the electrical resistance of water, has a 
similar effect upon its thermal resistance. As with electricity so with heat, we find that 
strong sulphuric acid has greater resistance than dilute. But in the case of heat we do 
not find that enormous difference in resistance between water and dilute sulphuric acid 
which is found with electricity. Nor are we justified in expecting it; for in the case 
of the electrical resistance of a mixture or compound of electrolytes the magnitude of 
the effect is measured ultimately by the degree of induced polarity; in the case of 
thermal resistance, it appears to depend arithmetically upon the quantities and respective 
resistances of the constituents. 
