VOL. LXXXII.] PHILOSOPHICAL TKANSACTIONS. 281 



the 2 tubes at 5.5 above 0. It was cooled down to 30°, and was found to sink 

 to I "20 below 0. I then heated it up to 6o°, and found the mixture in the 2 tubes 

 to stand at 5.5 above O as before. It was afterwards heated up to 100°, when 

 the mixture in the 2 tubes was found to have risen to 187 above O. I again 

 cooled it down to 30°, and found it to stand in the 2 tubes at 122 below O. 

 Lastly, I heated it again up to 6o°, and found it to stand in the 2 tubes at no 

 more than 4 above O. 



From the above experiments it appears, that the contraction of the mixture in 

 cooling down from 6o° to 30°, is 120 + 5.5 = 125.5; and the total expansion 

 on heating up from 30° to 100°, including the error arising from cooling it down 

 from 60° to 30°, will be 120 + 187 = 307; but in cooling down again from 

 100° to 30°, we shall have for the contraction 187 + 122 = 30g. The former 

 quantity of 307 errs from the experiments by weight 3.57, and the latter 1.'57 

 division, in defect. But by taking a mean of the quantities found on heating 

 the mixture up from 30° to 100°, including the error arising from son)e of the 

 fluid being left adhering to the tube, in cooling down from 6o° to 30° previous to 

 its being heated up from 30° to 100°, we shall have for the total expansion 

 307.25; and it was found in cooling down from 100° to 30° to be 309; the dif- 

 ference is 1.75; if then we say, as 182 : 1.75 :: 125.5 : 1.21, the last number 

 being subtracted from 307-25, we shall have for the true expansion in heating 

 up from 30° to 100°, 306.04; differing from the experiments by weight 4.53 

 divisions, in defect. 



From what was advanced by Mr. Ramsden respecting the accuracy of the 2 

 instruments with which the foregoing experiments have been made, there was 

 great reason to expect that different results would have been found. It appears 

 that no dependance ought to be placed on experiments made with that kind of 

 instrument which has a tube rising from the side of the ball, to be closed with a 

 stopper. More accuracy may undoubtedly be expected from experiments made 

 with the other kind of instrument which has 2 tubes, because one of the incon- 

 veniences attending the former is removed in it: but we have seen that even ex- 

 periments made with this instrument do not bear the same marks of accuracy as 

 the experiments by weight; nor can this be much wondered at, if it be consi- 

 dered that the trifling error of .027 of an inch, in constructing the instrument, 

 will produce an error of one division, which is equal to 0.24 of a grain on the 

 quantity contained in our weighing-bottle; and how difiicult and uncertain it is 

 in such an instrument to ascertain the exact temperature, by placing a thermo- 

 meter only by the side of it. It is not uncommon to see the fluid in the expan- 

 sion instrument, and the mercury in the thermometer, move contrary ways: and 

 I have more than once observed an alteration in the thermometer, of more than 

 half a degree, when no alteration whatever has been produced in the fluid in the 



VOL. XVII. O o 



