183 



exactly T - !- ( IZ2 J , that is, a lowering of temperature amount- 

 ing to 150 Cent. But the amount of cooling effect observed in the 

 experiment was only 13 Cent.; nor have we ever succeeded in ob- 

 serving (whether with thermometers held in various positions in the 

 stream, or with a thermo-electric arrangement constituted by a nar- 

 row tube through which the air flows, or by a straight wire of two 

 different metals in the axis of the stream, with the junction in the 

 place of most rapid motion, and in other positions on each side 

 of it,) a greater cooling effect than 20 Cent ; we therefore infer 

 that a body round which air is flowing rapidly acquires a higher 

 temperature than the average temperature of the air close to it all 

 round. The explanation of this conclusion probably is, that the 

 surface of contact between the air and the solid is the locality of the 

 most intense frictional generation of heat that takes place, and that 

 consequently a stratum of air round the body has a higher average 

 temperature than the air further off ; but whatever the explanation 

 may be, it appears certainly demonstrated that the air does not give 

 its own temperature even to a tube through which it flows, or to a 

 wire or thermometer-bulb completely surrounded by it. 



Having been convinced of this conclusion by experiments on rapid 

 motion of air through small passages, we inferred of course that the 

 same phenomenon must take place universally whenever air flows 

 against a solid or a solid is carried through air. If a velocity of 

 1780 feet per second in the foregoing experiment gave 137 Cent, 

 difference of temperature between the air and the solid, how probable 

 is it that meteors moving at from six to thirty miles per second even 

 through a rarefied atmosphere, really acquire, in accordance with 

 the same law, all the heat which they manifest ! On the other hand, 

 it seemed worth while to look for the same kind of effect on a much 

 smaller scale in bodies moving at moderate velocities through the 

 ordinary atmosphere. Accordingly, although it has been a practice 

 in general undoubtingly followed, to whirl a thermometer through 

 the air for the purpose of finding the atmospheric temperature, we 

 have tried and found, with thermometers of different sizes and va- 

 riously shaped bulbs, whirled through the air at the end of a string, 

 with velocities of -from 80 to 120 feet per second, temperatures 

 always higher than when the same thermometers are whirled in 



