362 PROFESSOR W. THOMSON AND MR. J. P. JOULE OX THE 
We have now adduced enough to illustrate the immense and sudden changes of 
temperature which exist in the « rapids” of a current of air, changes which point out 
the necessity of employing a porous plug, in order that when the air arrives at the 
thermometer its state may be reduced to a uniform condition. Figs. 4 Fig. 9. 
and 9 represent our first arrangement for the porous plug, wheie n is a 
brass casting with flange to bolt to the copper tube. It has eight studs, 
0 , and eight holes, pp, drilled into the inner part of the flange. I he 
studs and holes furnish the means of securing the porous materia » 
(in the present instance of cotton wool) in its place, by binding it down tighth’ with 
twine. Immediate contact between the cotton and metal is prevented by the mseition 
of a piece of india-rubber tubing ; qqq are three pieces of india-rubber tube mserte 
within each other, the inner one communicating with a glass tube r, through which 
the divisions of the thermometer may be seen, and which serves to convey the air to 
the meter In the experiments about to be given, the thermometer was in immediate 
contact with the cotton plug as represented in the figure, and the nozle was im- 
mersed in the bath up to the line .. The weight of the cotton wool m a dry state 
was 251 grs., its specific gravity 1*404, and being compressed into a space 1^ inch 
in diameter and 1*9 inch long, the opening left for the passage of air must have been 
equal in volume to a pipe to 1*33 of an inch diameter. 
First series of experiments. Atmospheric air dried and deprived of carbonic acid 
by quicklime. Gauge 73-6 ; barom. 30-04=14-695 lbs. pressure per square inch. 
Gauge. 
Total pressure 
iu lbs. per 
square inch. 
37-7 
37*9 
37*69 
35-854 
35-647 
35-866 
Cubic inches 
of air passed 
per minute 
reduced to 
atmospheric 
pressure. 
Temperature of hath* ascertained 
by Thermometer No. 1, in Centi- 
grade degrees. 
Temperature of the issuing air, 
ascertained by Thermometer No. 2, 
Cooliug 
effect. 
12703 
12703 
12703 
445 1 
445-5 ! 
445- 9 
446 
446- n 
446-6 ' 
446- 8 
447- 1 
447-2'1 
447-5 ■ 
447-8 
448 
445'6 =18-2676 
446-65 = 18-3128 
447-62 = 18-3545 
414-35=17-8298 
414 q 
414 I 
414-6 r 
414- 8J 
415- 4 ) 
tits )«6-46=.7-9C95 
417- 6 J 
418 1 
418- 2 I 
418-4 
418 j 
‘ i>418-15 = 18-0110 
0-4378 
0-3833 
0-3435 
A Liebig tube containing sulphuric acid, specific gravity I'S, gained 0-03 of a grain 
by passing through it, during the experiment, 100 cubic inches of air. 
. Bt varying the temperature of the water in which the coils were immersed, it was found that the tempe- 
rature of the water surrounding the first coil exercised no perceptible influence, the temperature of the rushmg 
air being entirely regulated by that of the termiual coil. However, the precaution was taken of keeping 
coils at nearly the same temperature. 
