VOL. LXXXIl.] PHILOSOPHICAL TRANSACTIONS. 269 



But there was another argument which still more forcibly determined us in favour 

 of the latter; namely, that the effect of mixture was found in that way, and 

 therefore we were sure it admitted of as great accuracy as was obtained in the 

 other part of the experiments. Greater nicety, if there had been a method 

 which allowed of it, would have been superfluous; and to incur the risk of less 

 accuracy would have been absolutely unjustifiable. By using the same method 

 to determine all the changes of specific gravity, those from heat as well as those 

 from mixture, a uniformity is given to the whole series of experiments, and no 

 one part of the results is liable to more suspicion than another. 



Till this time, I believe, the instruments with a ball and tube, for trying ex- 

 pansions, had all been constructed in the manner of real thermometers, to be 

 filled by means of heat; which circumstance, and the trouble attending it, was 

 a further objection to their use: but in the pamphlet above-mentioned are pro- 

 posed 2 instruments of this nature, to be filled without heat; one being provided 

 with 2 equal tubes, the other with a short tube, closed by a stopper. Though 

 both these instruments, and especially the latter, seemed liable to several causes 

 of error, yet, to remove doubts, and bring the method by weight to a proper 

 test, Mr. Gilpin was desired to make some trials with them; Mr. Kamsden, the 

 author of the pamphlet, having been previously requested to go through the 

 whole series of experiments on his own plan, which he declined to do. With 

 no small difficulty Mr. Gilpin got the instruments executed; and an account of 

 the experiments to which he subjected them shall be given, in his own words, at 

 the end of this report. From the perusal of that account, it will be perceived, 

 that the disagreement of the experiments among themselves, is nearly equal to 

 the quantity by which any of them differ from the expansions as obtained by 

 weight. On the whole however, they give the expansion somewhat less, the 

 cause of which I do not see; possibly it may depend on the fluid in the ball not 

 being quite heated and cooled to the degree shown by the accompanying ther- 

 mometer; possibly there may be a difference in the expansion of the glass with 

 which the instruments were made, and that of the weighing-bottle, for these 

 numbers are in both cases the excess of the expansion of the fluid over glass; or 

 it may turn on some other circumstance, which has eluded our attention. What- 

 ever may have occasioned the deficiency, I think the experiments will satisfy any 

 one, that most dependence is to be placed on the weights; and at all events the 

 difference is not such as to eff'ect the 3d place of decimals, or consequently the 

 tables intended for practice. 



Probably no one will be surprised that we did not think it necessary to make 

 trial of the weighing-bottle proposed by Mr. Ramsden. Not to mention other 

 inconveniences attending this instrument, it seems evident that a piece of flat 

 glass, with a thermometer projecting from it, laid down on the mouth of a bottle. 



