VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. 277 



instrument is 125 + 1.5 = 12fi.5; but in heating up again to 6o°, the expan- 

 sion was 125 + 1 = 126; the mean is 126.25. The expansion in heating up 

 from 60° to 100° was 183.5 — 1 = 182.5, but in cooling down again from 100° 

 to 60° the contraction was 183.5; the mean is 183; and therefore the total ex- 

 pansion from 30° to 100° will be 309.25, differing from the experiments by 

 weight 1.32 division, in defect. The difference between the 2 methods of heat- 

 ing up from 60° to 100°, and cooling down again from 100° to 60*^, is l division. 



It appears from all the preceding experiments with the mixture of equal parts 

 of spirit and water, that the mean of all the quantities found on heating up from 

 30° to 100°, and cooling down again from 100° to 30°, t;iken together is, for 

 the total expansion, 308.46 by the long instrument, and by the short one 309.29; 

 the former errs 2.11, and the latter 1.28 divisions, in defect, from the experi- 

 ments by weight; and that the mean of all the quantities found by the long in- 

 strument, in heating up from 30° to 100°, gives for the total expansion 0.33 di- 

 vision less than the mean of all the quantities taken together, by the same in- 

 strument, in cooling down from 100° to 30°. The difference by the short instru- 

 ment is 1.83 division. 



Though the results found from the preceding experiments come nearer those 

 of the experiments by weight than might have been expected, considering the 

 many objections that instruments of this kind must naturally present, and the 

 great differences which were actually found among themselves on repeating the 

 experiments, especially in the expansion of pure spirit, where the difference has 

 been equivalent to 1.68 gr. in weight, on the quantity used in oiir experiments 

 with the weighing-bottle; yet I think, after a careful perusal of the foregoing 

 facts, I shall not be thought too precipitate when I say, that these instruments 

 neither do nor can possess that accuracy which we have been led to expect from 

 them. We have seen, in the foregoing experiments, that there has sometimes 

 been apparently a loss of some part of the fluid, after an alteration of the tem- 

 perature; at other times there appeared to be no loss at all; and sometimes there 

 appeared to be even more spirit in the instrument than there was at first. These 

 contradictory facts may, I apprehend, be accounted for in the following manner. 

 The mechanical operation of grinding a stopper that will fit so delicate a tube, 

 as is here necessary, perfectly tight, must be acknowledged to be difficult; and 

 should it happen to be done accurately, so that none of the fluid is lost in one 

 degree of temperature, it is very doubtful whether, on exposing this instrument 

 to a different temperature, the expansion would be the same in both the tube and 

 stopper. It appears most probable, from these experiments, that they actually 

 did not expand alike, as perhaps no 2 pieces of glass ever do; and the effect to be 

 expected from a less expansion of the stopper than of the tube is, either that 

 some of the fluid would leak out, or that the capacity of the ball would be en- 



