- . Prophgation of Heat in Pluids. 335 
fia thofe motions would retard that effet: To determine 
this point, a certain quantity of heat was mdde to pdfs 
through a given quantity of pure water; and, noting the 
time employed, the experitnent was repeated with water 
mixed with fome fine fubftance, as eider-down, which, 
without altering its chemical ptoperties, or impairing its 
fluidity, could only ferve to obftruét and embarrafs the mo- 
tions of the particles of the water in tranfporting the heat, 
fhould heat be tran/ported and) carried in this manner, and 
not pafs freely through it, 
The body which received the heat, and which ferved at 
the fame time to meafure the quantity of it communicated, * 
was avery large thermometer cf (Plate IX. fig: '1.); with a 
eylindrical bulb. c made of thin copper; {pherical at the 
ends; 1°84 inches in diameter, 4:99 long, of 13°2099 cubic 
inches capacity; and meafuring externally 28-834 {quare 
inches: it weighed 1846 er. and could contain 3344 gr. of 
water at the teniperature of 55°... To this bulb was affixed 
a glafs tube ef (reprefented in the plate as broken off at f) 
24 inches long and ;*, of ah inich in diameter, by means of 
a cork fitted into a neck of copper t inch long; belonging 
to the bulb: This thermometer, filled with linfeed oil and 
graduated, was fixed in the axis of a hollow cylinder (a bis 
a feétion. of it) made of thin fheet-copper 114. inches long, 
and 2°3435 inches diameter within, with a fpherieal bot- 
tom, weighing 2261 gr. The bulb of the thermometer was 
made to occupy the lower part of this. cylinder by means of 
4 pins of wood ,% of an inch in diameter and + of an inch 
long, one of them faftened to the bottem, the other three 
round the infide of the cylinder at equal diftances, in very 
fmall fockets made to receive them. (Thefe pins may be 
 feen at the lower part of jig. 1. and alfo in fig. 2. which 
reprefents a horizontal fection of the cylinder and a bird’s- 
eye view of the thermometer in its place.) The: diftance 
_ between the externa! furface of the bulb of the thermometer 
| 
and the internal of the contaming cylinder was .0°25175 of 
Aa2 an 
