INVESTIGATIONS RELATIVE TO ILLUMINATING MATERIALS. 485 



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

 militate against it-s 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 liuids, 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 tlie 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 i)0wer 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 (iapillarity, because 

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

 had less capillarity — that is, less elevating i)ower in a flue tube — had 

 greater power in ascending in the meshes of a wick. 



The relative fluidity of the diflerent oils was obtained by flUing in 

 succession a ijear-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 fllled vcith 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 proportional to 

 gravity, tlie heavier the liquid the greater would be the power required 

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

 or, in 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 mercury, and then the same bulk of 

 distilled water, were allowed to run out of the A^essel 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 107. 



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 tlie 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 temijerature above that of the atmosphere on 

 the flowing of the two oils was observed. By this means the important 

 fact was elicited that as the temi)erature was increased the liquidity ot 

 the lard increased in a more rapid degree than that of the sperm, and 

 that, at the temperature of about 250° F., the li(piidity of the former 

 exceeded that of the latter. 



A simil'ir series of experiments was made in regard to the rapidity' ot 

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

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



