VOL. LXXXII.] 



PHILOSOPHICAL TRANSACTIONS. 



139 



coverings which were formed were very different, owing to the different dispo- 

 sition of the material. The raw silk was very fine, and was very equally dis- 

 tributed through the space it occupied, and it formed a warm covering. The 

 ravelings of tafFety were also fine, but not so fine as the raw silk, and of course 

 the interstices between its threads were greater, and it was less warm; but the 

 cuttings of sewing silk were very coarse, and consequently it was very unequally 

 distributed in the space in which it was confined; and it made a very bad cover- 

 ing for confining heat. It is clear, from the results of the last 5 experiments, 

 that the air which occupies the interstices of bodies, made use of for covering, 

 acts a very important part in the operation of confining heat. 



Having found that the fineness and equal distribution of a body or substance 

 made use of to form a covering to confine heat, contributes so much to the 

 warmth of the covering, I was desirous, in the next place, to see the effect of 

 condensing the covering, its quantity of matter remaining the same, but its 

 thickness being diminished in proportion to the increase of its density. The ex- 

 periment made for this purpose was as follows: — I took l6 grains of common 

 sewing silk, and winding it about the bulb of the thermometer in such a 

 manner that it entirely covered it, and 

 was as nearly as possible of the same 

 thickness in every part, I replaced the 

 thermometer in its cylinder and globe, 

 and heating it in boiling water, cooled 

 it in ice and water, as in the fore- 

 going experiments. The results of 

 the experiment were as may be seen in 

 the annexed table; and in order that 

 it may be compared with those made 

 with the same quantity of silk differ- 

 ently disposed of, I have placed those 

 experiments by the side of it: 



The following table shows the results of like experiments, with the threads of 

 various kinds; and that they may the more easily be compared with those made 

 with the same quantity of the same substances in a different form, I have placed 

 the accounts of these experiments by the side of each other. I have also added 

 the account of an experiment, in which l6 grains of fine linen cloth were 

 wrapped round the bulb of the thermometer, going round it 9 times, and being 

 bound together at the top and bottom of it, so as completely to cover it. In 

 each of these experiments 16 grains of each of the substances were wound round 

 the bulb of the thermometer. 



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