FREDERICK GUTHRIE OH THE THERMAL RESISTANCE OE LIQUIDS. 639 
§ 12. Count Rumford* * * § froze some water at the bottom of a cylindrical vessel. Upon 
this he poured a known quantity of warm water. After a time the liquid contents of 
the vessel were again determined, and the increase was found to be so small that it was 
concluded to arise wholly from the direct contact of the ice with the warm water in the 
first instance. Count Rumford also took two cylinder glasses containing ice frozen to 
the bottom. Into one he poured boiling water, and into the other an equal weight of 
water at 0° C. In both cases the ice soon became covered with a layer of water at 
its maximum density (4° C.). After a time the ice was removed from both vessels and 
weighed. From the result the experimenter concluded that the quantity melted was 
nearly the same, and that consequently the water did not conduct the heat. 
§ 13. Dr. Th. Thomson f gently heated from below a column of coloured water covered 
with a column of colourless water, and found that the heat ascended even when no 
coloration of the upper water-layer took place, and when therefore no sensible diffusion 
or convection occurred. Such an experiment must be unsatisfactory for reasons already 
mentioned, unless indeed the water have the initial temperature of between 0°and 4° C., 
and the lower portion be heated to not above 4° C. In this case only can the water 
possibly remain in equilibrium, the denser layers being then the lower ones. 
§ 14. Mr. J. Murray $ employed a hollow cylinder of ice as the vessel to contain the 
liquid under examination. In such a cylinder he placed successively mercury and oil at 
0° C. The upper surface of the liquid was heated by means of a vessel of water at 100° C., 
supported in some cases a little above the liquid, in others in actual contact with it. 
The object of the ice-cylinder was to get rid of conduction, because the ice on receiving 
heat does not become warmer, — it melts. But, as pointed out by M. Despretz, the 
existence of the melted ice and the partial destruction of the vessel complicate and in a 
great measure invalidate the results. Indeed, in some respects, ice is the worst substance 
which could be chosen, on account of the distortion of the results due to the great latent 
heat of water and the small specific heats of mercury and oil. But although quantitative 
results were out of the question, Mr. Murray succeeded in establishing the fact, which 
we shall find confirmed, that mercury is a better conductor of heat than oil. 
§ 15. The question was in this unsatisfactory state when M. Despretz published his 
first memoir § on the subject. M. Despretz filled with water a wooden cylinder painted 
internally 1 metre high and from 0*218 to 0*405 metre internal diameter, the thickness 
of the sides being 28 millimetres. At equal intervals down the axis of the cylinder were 
the bulbs of horizontal thermometers whose stems pierced the side of the cylinder. The 
column of water was heated from above by means of a copper vessel, the bottom of 
which was in contact with the upper surface of the column. Into this vessel fresh 
portions of hot water were poured at intervals of from four to five minutes. After 
* Rumford, Essays, vol. ii. p. 199. 
f Nicholson’s Journal, vol. i. p. 81. 
X Arch. vol. rxlii. p. 195 ; also Gehler’s Worterbucli, Art. "Warme. 
§ Despretz, Ann. de Chim. et de Phys. 1839, p. 206. Also Comptes Rendus, 1852, p. 540. 
4 q 2 
