in various Substances. 451 



cupying a greater space, is no more than what I expected, 

 from the idea I had formed of the causes of the warmth 

 of covering; but I confess I was much surprised to 

 find that there is so great a difference in the relative 

 warmth of these two coverings, when they are employed 

 to confine great degrees of Heat, and when the Heat 

 they confine is much less in proportion to the tempera- 

 ture of the surrounding medium. This difference was 

 very remarkable ; in the experiments with sheep's-wool, 

 and with woollen thread, the warmth of the covering 

 formed of 16 grains of the former was to that formed 

 of 1 6 grains of the latter, when the bulb of the ther- 

 mometer was heated to 70 and cooled to 60, as 79 to 

 46 (the surrounding medium being at o) ; but after- 

 wards, when the thermometer had only fallen from 20 

 to 10 of Heat, the warmth of the wool was to that of 

 the woollen thread only as 426 to 410 ; and in the ex- 

 periments with lint, and with linen thread, when the 

 Heat was much abated, the covering of the thread ap- 

 peared to be even warmer than that of the lint, though 

 in the beginning of the experiments, when the Heat was 

 much greater, the lint was warmer than the thread, in 

 the proportion of 80 to 46. 



From hence it should seem that a covering may, 

 under certain circumstances, be very good for confining 

 small degrees of warmth, which would be but very in- 

 different when made use of for confining a more intense 

 Heat, and vice versa. This, I believe, is a new fact ; 

 and I think the knowledge of it may lead to further 

 discoveries relative to the causes of the warmth of cover- 

 ings, or the manner in which Heat makes its passage 

 through them. But I forbear to enlarge upon this sub- 

 ject, till I shall have given an account of several other 



