together with some remarks upon sensible cold. 73 



The circumstances that particularly engaged my attention 

 were wind, and moisture. With these views the following 

 experiments were made, and verified by repeated trials. 



Experiment i. 



1 82 1 , January 3. A strong east wind. 

 The temperature of the air 31°. 



The thermometer in this, and all the 

 experiments, being previously raised 

 to 100°, in the manner before-men- 

 tioned, the descent of the mercury 

 from that point was observed as fol- 

 lows : 



After 10" it was 78®. Decrement 22** 



20" 60° 18° 



30" 52° 8° 



By the decrements, it is to be under- 

 stood the descent in each successive 

 ten seconds. This is added, because I 

 consider it as the proper measure of 

 the sensible cold, so long as the ther- 

 mometer retains a heat approaching to 

 that of the human body. 



Experiment 2. 

 1821, Jan. 4. No perceptible wind. 

 The temperature of the air 30°, the 

 atmosphere hazy. 

 After 10" therm. 89® Decrement 11* 



20" 800 III 9*> 



30" 71° 9° 



Experiment 3. 

 1 8a I, Feb. 10. A strong east wind. 

 Temperature of air 47°. The atmo- 

 sphere clear, with sunshine. 

 After 10" therm. 82° Decrement 18° 



20" 

 30" 



73° 

 640 



Experiment 4. 

 1 824, Jan. 9. A cold fog. No wind. 

 Temperature of the air 370. 

 After 10" therm. 92° Decrement 8*^ 



20" 85° 70 



30" 790 6° 



The most superficial view of these experiments shows the 

 prodigious effect of wind to increase the rate of cooling, which, 

 I apprehend, constitutes sensible cold ; so that in experiment 3, 

 though the thermometer suspended in the open air was 17° 

 higher than in experiment 2, yet the sensible cold was very 

 considerably greater ; but when there was no wind, even a 

 wet fog did not much, if at all, increase it. This, which at 

 first sight may appear contradictory to experience is not, I 

 believe, really so ; for though the power of such air to carry 

 off the heat of the body be indeed increased, yet so long as 

 we remain at rest, we are in great measure unaffected by it ; 



MDcccxxvr. L 



