268 PHILOSOPHICAL TRANSACTIONS. [aNNO 179'2. 



liable to the following objections. 1. The difficulty of obtaining the full pene- 

 tration of the spirit and water, in a vessel of the shape required, where, by the 

 intervention of such a narrow neck as is wanted, the free agitation of the fluid 

 must be greatly impeded. 2. The difficulty of getting out all the air-bubbles, 

 ])roduced by the shaking, &c. in a vessel so shaped. 3. The difficulty, or almost 

 impossibility, of bringing the mixture, by the repeated fillings, to coincide ex- 

 actly with the ring on the neck: for this purpose, the last quantities of water 

 must be put in by such small portions at a time, that scarcely any attention will 

 be equal to tlie task; and if at length too much be added, it cannot be taken 

 out again without injuring, in some degree, the accuracy of the experiment, 

 which depends on combining the precise quantity of water required to fill the 

 vessel up to the mark, when the full penetration has taken place. 4. In opening 

 the vessel so frequently to fill it up, a sensible part of the spirit must be lost by 

 evaporation. 5. Further, it is necessary that, at the end of the operation, the 

 fluid should throughout be exactly of the same temperature as the pure spirit 

 was in the preparatory experiment with it alone: the difficulty of effecting and 

 determining which must be obvious to every one, especially in a vessel of such a 

 size and shape. Lastly, as this vessel is much less manageable than the weigh- 

 ing-bottle, I think the fluid in it cannot be brought to the mark with nearly the 

 same degree of accuracy. These objections, joined to the consideration that no 

 object can be attained in this way, which was not accomplished, with at least 

 equal accuracy, and probably no greater trouble, by weighing the spirit and 

 vi'ater separately, determined us not to attempt any experiments with such an 

 instrument. 



Thirdly, it is now to be explained why we undertook to determine the effect 

 of heat and cold on the fluids, by means of the weighing-bottle. When, pre- 

 paratory to our former experiments, that part of the subject came under consi- 

 deration, the method of ascertaining the expansions and contractions, by means 

 of instruments like thermometers, was one of the first that presented itself. On 

 this occasion, Mr. Cavendish was so good as to mention some experiments made 

 by his father, Lord Charles Cavendish, with instruments on that construction, 

 for the very purpose of determining the expansion of fluids; and other experi- 

 ments, of the same nature, have appeared in print. The application of this 

 method however was thought liable to a most important objection, from the great 

 difficulty there is of being sure that the spirits in the ball are exactly of the tem- 

 perature indicated by the thermometer placed by the side of it. To enlarge on 

 this circumstance would be useless, as every person accustomed to experiments is 

 aware, that all possible precautions, joined to the utmost attention in the ob- 

 server, are scarcely sufficient to ensure this essential correspondence of tempera- 

 ture; which reason alone would have induced us to prefer the method by weight. 



