24S Biographical Account of [April, 



Weight. 



Olive oil burnt in a common lamp, with a clear bright^ ^ 



flame without smoke / 



Rape oil. Burnt in the same manner 125 



Linseed oil. Likewise burnt in the same manner 120 



But it is necessary to observe that these experiments were after- 

 wards repeated by M. Hassenfratz, who obtained a very different 

 result. He found that more oil must be consumed to produce the 

 same quantity of light in an Argand's lamp than in a common 

 lamp. 



7. An Account of some Experiments on Coloured Shadows, 

 Phil. Trans. 1794. P. 107.--lt is well known that when two 

 shadows are cast upon paper, one illuminated by the light of day or 

 of the moon, the other by the light of a candle, the first appears 

 blue, the second yellow. Count Rumford observed this by accident, 

 and he was induced to make a set of experiments on the subject. 

 He found that the two colours could be produced by two candles by 

 interposing a pane of yellow or blue glass before one of them. 

 When two rays of light from different parts of the heavens on a 

 windy day were made to illuminate two shadows, a most fascinating 

 succession of colours took place, all perfectly harmonious, and ex- 

 hibiting every possible variety. He found that the blue colour was 

 merely an optical deception, being always produced when the other 

 shadow was yellow. But when he surveyed the blue shadow alone 

 through a long tube which excluded from sight the yellow shadow 

 and all surrounding objects, no blue colour was perceptible. 



8. Experiments to determine the Force of fired Gunpowder. 

 Phil. Trans. 1797. P. 222. — This is perhaps the most curious and 

 Interesting of all Count Rumford's papers. The experiments are 

 very ingenious, and appear to have been well conducted ; though 

 the conclusions which he deduces from them are by no means satis- 

 factory. Robins estimated the force of gunpowder at 1000 atmos- 

 pheres ; Daniel Bernouilii, at 10,000 atmospheres; and Dr. 

 Hutton, at 2000. Count Rumford endeavours to prove in this 

 paper that the force is equivalent to 50,000 atmospheres. But his 

 mode of reasoning is not correct. Twelve grains of gunpowder 

 were found to move a weight of 8800 lbs. out of its place. There 

 is no difficulty in calculating the quantity of elastic fluid formed 

 during' the combustion of a given quantity of giKipowder, sup- 

 po.>.ing the whole of it to be consumed. 100 grains of gunpowder 

 contaii? usually about 67*3 grains of nitre. This quantity of nitre 

 contains 35'8 grains of nitric acid, equivalent to 78 cubic inches of 

 '^^yo'"'' g"3 and 32 cubic inches of azotic gas, making a total of 

 liO cubic inches. Now as gunpowder is rather lighter than the 

 same bulk of water, we shall not err much if we suppose 100 grs. 

 of gunpowder to occujjy the bulk of-} of a cubic inch ; so that the 

 gas in the powder is equivalent to 330 atmospheres. Tltis gas is 



