270 PHILOSOPHICAL TRANSACTIONS. [aNNO l/Ql. 



cannot be depended on to push off the superfluous liquor equally every time; 

 and that the proper wiping of the bottle, when so covered, will be attended with 

 difficulties of various kinds. 



It is true that the experiments by weight took up much time, and demanded 

 great patience. But I believe that similar experiments, by the methods recom- 

 mended in the pamphlet, if executed with the same degree of accuracy, would 

 be found not much less tedious. However this may be, it is a consideration of 

 no consequence, provided the results at length obtained be right. Now of these 

 there is no direct impeachment, though some doubts are thrown on them, on 4 

 accounts; evaporation; condensation of moisture on the weighing-bottle; diffi- 

 culty of shaking the fluid in it; and uncertainty in determining the heat. With 

 regard to evaporation, its effect, we hope, has been ascertained, and allowed for, 

 in these new experiments. All error from condensation of moisture was obviated 

 by careful wiping. The fluid in the weighing-bottle was agitated, and mixed to- 

 gether, by means of the thermometer immersed in it; besides which, a consi- 

 derable degree of motion could be given to it, even when the ball was very nearly 

 full, by shaking the bottle in various directions. Mr. Gilpin's known accuracy, 

 and the care he bestowed on these experiments, must gain him credit for having 

 duly watched the thermometer, so as to seize the moment when it gave the just 

 temperature of the mass. 



Our experiments were finished, and the tables now given were drawn out, be- 

 fore the appearance of Mr. Ramsden's pamphlet. Yet if any of the methods he 

 proposed had been really preferable, the whole series should have been repeated 

 on that new plan, and particularly with regard to the effect of heat, if the in- 

 struments for that purpose had been found to answer the character given of them. 

 But as this was not the case, we have thought it right to adhere to an obvious 

 and direct method, in which, however laborious, there can be no fallacy, and 

 the uniformity of which ensures an equal degree of accuracy to every part of the 

 operation. 



Since the publication of our first tables, several hydrometers have been con- 

 trived, with the view of applying them to practice. Those of copper were re- 

 jected on account of the errors which small and almost imperceptible bruises in 

 them might occasion; and for the same reason no other metal was tried. Mr. 

 Gilpin has constructed 2 areometers of glass; one with the stem so divided that 

 an easy table may be formed for the correction necessary according to the dif- 

 ferent weights with which it is used; the other with a separate scale fixed to each 

 of those weights, made to slip into the tubular stem of the instrument; a con- 

 trivance that obviates the necessity of a table. Mr. Ramsden also has invented 

 a balance hydrometer, with several varieties of construction, one of which is 

 detailed in his pamphlet. All the above-mentioned instruments appear to have 



