1815.] Sir Benjamin Thompson, K?if. Count Rimford. 245 



size and weight is known. According as the powder under exami- 

 nation drives the bullet with more or less velocity than this powder, 

 it is above or below the standard. From Robins's theory it follows, 

 that when bullets of the same size, but of different weights, are 

 discharged from the same piece by the same quantity of powder, 

 their velocity is reciprocally as the square roots of their weights. 

 But our author shows that there are circumstances which prevent 

 this theory from holding good in all cases. The explosive force of 

 aurumfidminans he found equivalent to about 307 atmospheres, or 

 about i- of that of gunpowder.* The specific gravity of gunpowder 

 he found 1-745. When well shaken, its weight, compared to the 

 same bulk of water, was 0-'J37 to 1-000, and when lying loose as 

 ' 0-836 to 1-000. He attempted to increase the force of gunpowder 

 by mixing it with carbonate of potash, sal-ammoniac, and brass 

 filings ; but the effect was the reverse of his expectation, l he 

 swimming bladders of small fish filled with water or alcohol, and 

 put into the middle of the charge, likewise diminished the effect 

 very considerably. 



2. New Experiments on Heat. Phil. Trans. 1786. P. 2/3 



A thermometer surrounded with different mediums was plunged 

 into boiling water, or into melting ice, and the times that elapsed 

 during the heating or cooling were considered as indicating the 

 conducting power of the different mediums inversely. The follow- 

 ing table exhibits the conducting power of the different mediums 

 tried according to these experime^t^i : — 



Mercury 1000 



Moist air , , , , 330 



\Vater 342 



Common air, density 1 gO^. 



Rarified air, density ± 80i 



Rarified air, density -'^ 78 



The Torricellian vacuum 55 



But before the conducting power of these substances can be 

 concluded from these experiments, it would be necessary to take 

 into view their specific heats, and likewise thg radiation of heat 

 through different elastic mediums. 



3. Experiments on the Production of Dephlogisticated Air from 



Water with various Substances. Phil. Trans. 1787. P. 84. 



Dr. Ingenhousz had discovered that when the leaves of plants arc 

 put under water, and exposed to the rays of the sun, a quantity of 

 oxygen gas is evolved ; and Dr. Priestley had obscr\ed that when 

 water became green it always yielded more of this gas than common 

 water. On these experiments a theory liad been founded that vegeta- 

 bles decompose water, retaining the hydrogen, and giving out the 

 oxygen, and that hy this process the oxygen taken from common 



• I conceive its force docs not exceed t'u "i of that of gunpowder.— T. 



