INVESTIGATIONS RELATIVE TO ILLUMINATING MATERIALS. 485 



be due in part to the imperfect liquidity of the oil, which would also 

 militate against its use in mechanical lamps. 



The lard-oil was subjected to experiments in regard to each of .these 

 points. It was found, by the usual method of weighing equal quantities 

 of the two fluids, that the specific gravity of the lard was greater than 

 that of the sperm ; and also by dipping two portions of the same wick 

 into the two liquids, and noting the height to which each ascended in a 

 given time, that the surface attraction of the sperm was greater than 

 that of the lard, or, in other words, the ascensional power of sperm was 

 much greater than that of lard at ordinary temperatures. This method 

 was also employed in obtaining the relative surface attraction of various 

 other liquids ; we say surface attraction instead of capillarity, because 

 it was found in the course of these investigations that substances which 

 had less capillarity — that is, less elevating power in a fine tube — had 

 greater power in ascending in the meshes o^ a wick. 



The relative fluidity of the different oils was obtained by filling in 

 succession a pear-shaped vessel, with a narrow neck, of about the ca- 

 pacity of a pint, having a hole in the lowest part of the bottom of about 

 a tenth of an inch in diameter. Such a vessel filled with any number 

 of perfect liquids would be emptied in the same time, whatever their spe- 

 cific gravity. As at any given horizon, inertia is directly i)roportional to 

 gravity, tbe heavier the liquid the greater would be the ])ower required 

 to move it, but the motive power would be in proportion to the pressure, 

 or, iu other words, to the weight, and therefore all perfect liquids should 

 issue from the same orifice with the same velocity. To test this propo- 

 sition, eight fluid ounces of clean mercurj^, and then the same bulk of 

 distilled water, were allowed to run out of the vessel above mentioned; 

 the time observed was the same within the nearest second. It was found, 

 in repeating this experiment with sperm and lard oils that the rapidity 

 of the flow of the former exceeded considerably that of the latter; the 

 ratio of time being 100 to 1G7. 



The results thus far in these investigations were apparently against 

 the use of lard-oil; it was observed however in the experiments on the 

 flow of the two oils on different occasions, that a variation in the time 

 occurred, which could be attributed only to a variation in the tempera- 

 ture at which the experiments were made. In relation to this point the 

 effect of an increase of the temfierature above that of the atmosphere on 

 the flowing of the two oils was observedv By this means the important 

 fact w\as elicited that as the temperature was increased the liquidity of 

 the lard increased in a more raj^id degree than that of the sperm, and 

 that, at the temperature of about 250° P., the liquidity of the former 

 exceeded that of the latter. 



A similar series of experiments was made in regard to the rapidity of 

 ascent of the oil in the wick, and with a similar result. At about the 

 temperature of that before meutidned, the ascensional power of the lard 



