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XIX. On the Thermal Effects of Fluids in Motion. — Part III. On the Changes of Tem- 
perature experienced by bodies moving through Air. By Professor W. Thomson, 
A M., LL.D., F.E.S. &c., and J. P. Joule, LL.D., F.B.8. & c . 
Eeceived June 21, — Eead June 21, 1860. 
This interesting branch of our researches has been prosecuted by us from time to time 
since 1856. In the spring of that year we commenced our experiments by trying the 
effect of whirling thermometers in the air. This process had been confidently recom- 
mended as a means of obtaining the temperature of the atmosphere, but we were sure 
that the plan was not absolutely correct, and one of us had, as early as 1847, explained 
the phenomena of “ shooting stars ” by the heat developed by bodies rushing into our 
atmosphere. In our early experiments we whirled a thermometer by means of a string, 
alternately quickly and slowly, and it was found that the thermometer Avas invariably 
higher after quick than after slow whirling, in some cases the difference amounting to 
as much as a degree Faheenheit. We also succeeded in exhibiting the same pheno- 
menon by whirling a thermo-electric junction. In 1857 we resumed the subject, using 
an apparatus consisting of a wheel worked by hand, communicating rapid rotation to 
an axle, at the extremity of which an arm carrying a thermometer, with its bulb out- 
wards, was fixed. The distance between the centre of the axle and the thermometer 
bulb was 39 inches. The thermometers made use of were filled with ether or chloro- 
form, and had, the smaller 275, and the larger 330 divisions to the degree C. The 
lengths of the cylindrical bulbs were and 1^ inch, then* diameters *26 and -48 of 
an inch respectively. The method of experimenting Avas to revolve the thermometer 
bulb at a certain velocity until we knew by experience that it had obtained the full 
thermal effect, then to stop it as suddenly as possible and observe the temperature. 
Alternately Avith these observations others Avere made to ascertain the temperature 
after a slow velocity, the effect due to which Avas calculated from the other observations, 
on the hypothesis that it varied Avith the square of the velocity. In all cases the results 
in the Tables are means of several experiments. 
2 X 
MUCCCLX. 
