563 



TABLE VIII. Smaller Thermometer whirled along with glass globe. 

 Rise in divisions of scale. 



The effects of fluid friction are strikingly evident in the above 

 results, particularly at the slow velocities of 3 and 7 feet per second. 

 It is clear from these, that the air, after coming in contact with the 

 front of the globe, traverses with friction the equatorial parts, giving 

 out an accumulating thermal effect, a part of which is carried round 

 to the after pole. At higher velocities the effects of friction seem 

 rapidly to diminish, so that at velocities between 23 and 38 feet per 

 second, the mean indication of thermometers placed all round the 

 globe would be nearly constant. Our anticipation (written before 

 these latter experiments were made), that a complete verification of 

 the theory propounded at the commencement was impossible with 

 our present means, is thus completely justified. 



It may be proper to observe, that in the form of experiment 

 hitherto adopted by us, the results are probably, to a trifling extent, 

 influenced by the vortex of air occasioned by the circular motion. 



We have on several occasions noticed the effect of sudden changes 

 in the force of wind on the temperature of a thermometer held in it. 

 Sometimes the thermometer was observed to rise, at other times to 

 fall, when a gust came suddenly on. When a rise occurred, it was 

 seldom equivalent to the effect, as ascertained by the foregoing ex- 

 periments, due to the increased velocity of the air. Hence we draw 

 the conclusion, that the actual temperature of a gust of wind is lower 

 than that of the subsequent lull. This is probably owing to the air 

 in the latter case having had its vis viva converted into heat by 



