FREDERICK GUTHRIE OK THE THERMAL RESISTANCE OP LIQUIDS. 643 
travels downward through the liquid L, warms the platinum face of B, expands the air 
in B, and depresses the water in Q. 
§ 27. The arrangement for leading a current of water of constant temperature 
through A is shown in tig. 3, Plate LXY. A tinned iron cylindrical vessel containing the 
water, 1, about 1 metre high and 30 centims. diameter, is heated by a gas-lamp, 2. The 
gas supplying the lamp passes through the thermostat, 3. Supported near the bottom 
of the cylinder is a perforated conical mixer, 4*. In the immediate neighbourhood of 
the bulb of the thermostat is the bulb of the standard thermometer, 5, a small suspended 
beaker glass, 6, and the shorter limb of the siphon tube, 7. The longer limb 8 of the 
siphon may be introduced into the funnel 9 connected with the tube C of the diathermo- 
meter. The diathermometer itself, 10, is firmly clamped upon a substantial three-legged 
camera-stand, 11, and a wooden screen, 12, is placed between the lamp and cylinder, 
2 and 1, and the diathermometer. A tube attached to the tube D of the diathermometer 
conveys away the warm water which has passed through the cone A. When one expe- 
riment has been made and the instrument has been readjusted by passing cold water 
through A, the cone A is emptied by forcing air through D ; by this means there 
always remains a film of water on the bottom of A of about 0‘5 millim. in thickness. 
§ 28. Let us suppose that an experiment has to be made, that the diathermometer 
has been adjusted, and that the temperature in 1 is the required temperature. The 
siphon 7, 8 is hung away from the diathermometer and the water is set running through 
it. About 5 s before the appointed time, the beaker, 6, full of warm water is brought 
to the edge of the funnel, 9. At the appointed time it is emptied into the funnel, into 
which is immediately placed the end of the siphon, 8. A continual flow of hot water 
takes place through the cone A, the base of which is therefore thenceforth maintained 
at a temperature a given number of degrees above the temperature of the air, that is, 
above the temperature of the liquid, L. 
§ 29. The thermometer used was a standard Kew thermometer, the error of which 
was determined. The readings subsequently given are all reduced to Centigrade. 
IV. Sources of Error and Corrections. 
§ 30. It is clear that when the hot water passes through the siphon, 7, 8, into the cone 
A, the water in A is somewhat cooler than in 1, in consequence of the radiation from 
the siphon and cone and of the atmospheric convection. It is necessary therefore to 
estimate this loss of heat in order to know at what temperature the water in 1 must be 
kept, so that the water in A may have the required temperature. 
§ 31. The temperature of the air, T, being 18°T6 C., it was found that, 
When the temperature in 1 was .... 
28-16 
38-16 
48-16 
Then „ „ A „ . . . . 
27-88 
37-51 
46-40 
Loss .... 
0-28 
”(>65 
1-76 
* For description of thermostat and mixer, 
see Phil. Hag, 
July 1868. 
