336 
OX THE THEEHAL EEFECTS OF FLEIDS IX HOTIOX. 
produce a difference of level in the tubes h and d equal to 2'5 inches, hen c was put 
in the equatorial position, there was, on the contraiT, a suction equal to 1 -2 inch. "SMien 
c was made the posterior pole there was also a suction, equal, however, to only Off inch. 
Having tied a thick fold of silk over the orifice cZ, we tihff the same thing in a strong 
breeze of wind, when we found that on making c the anterior pole, we had a pressure 
amounting to 0-6 of an inch; on making c equatorial, a suction of 0-3; and on making 
c the posterior pole, a suction of 0'05 inch. 
We have not hitherto been able to detect any change in the thermal effect, owing to 
the whistling sound of wire or other bodies rapidly whirled. We think it possible that 
this vibratory action decreases the resistance and the evolution of heat. Some of the 
sounds produced are interesting and w^orthy of further investigation. When a small 
piece of paper was attached to the revolving wu’e, we obtained a continuous succession 
of loud cracks similar to those of a whip. 
But although this and other parts of our subject remain to be cleared up, we believe 
that it Avill be found that at all high velocities the thermal effect arises entirely fi'om 
stopped air, and thus is independent of the shape and mass of the body, and of the 
temperature and density of the atmosphere. From some experiments described in the 
‘Proceedings of the Koyal Society’ of June 19, 1856, p. 183, we uiferred that a body 
placed in a stream of air moving with a velocity of 1T80 feet per second, was raised 
137° C. above the temperature of that stream. This gives 152 feet per second as the 
velocity due to 1°, while our direct results, given in the present paper, indicate 179. 
It must be obvious that a thermometer placed in the wind registers the temperature 
of the air, plus the greater portion, but not the whole, of the temperature due to the 
vis viva of its motion. In a place perfectly sheltered from the wind, the temperatiu-e of 
a thermometer immersed in the air will be that of the nfind, plus the whole temperature 
due to the vis viva of the moving air. In accordance with this we have found that a 
thermometer placed in a sheltered situation, such as on the top of a Avail opposite the 
wind, indicates a higher temperature than Avhen it is exposed to the blast. A minute 
examination of these phenomena cannot fail to interest the meteorologist. 
