162 ANNUAL OF SCIENTIFIC DISCOVERY. 



tube, and a flat or elliptical bore for the narrow one, the greatest diameter of 

 which equals the diameter of the wide bore. In graduating, if, when the 

 instrument is vertical, the narrow bore being beneath, the mercury fills the 

 bulb and rises in the wide bore, then the wide bore may be pointed off at 

 different temperatures like an ordinary thermometer; but if under these 

 circumstances the mercury does not rise in the wide bore, then, in order to 

 point off the wide bore, the instrument must be laid horizontally in a dish of 

 water, and compared with a standard thermometer at different temperatures ; 

 the extremity of the mercury in the narrow bore being always kept at a fixed 

 point. When the wide bore has been pointed off we may, by running the 

 mercury along, find what length of the narrow bore corresponds to a certain 

 length of the wide one, and thus be enabled to point off the narrow bore. 

 In using the instrument it should be kept nearly horizontal, and there is pro- 

 bably for each instrument a small range of inclination, for every position 

 within which its peculiar action holds, but beyond which it is interfered with 

 by gravity. Before graduating such an instrument it should be ascertained 

 whether it is likely to answer, and the best test seems to be to lay it hori- 

 zontally, exposing it to changes of temperature of the same nature with those 

 which it is intended afterwards to measure; if its action be perfect, the 

 mercury will eventually be found to have retreated into the bulb from the 

 narrow bore ; but, should it have stopped at any point, the action will only 

 be perfect up to that point. If this demands too much time, it may be tested 

 by repeatedly applying to the bulb of an instrument so placed a few drops of 

 slightly warmed water. 



RESEARCHES RESPECTING HEAT, LIGHT, ETC. 



The recent investigations of Mr. Joule of Manchester, and Professors 

 Thomson and Eankine of Glasgow, relative to the mechanical equivalent of 

 heat, have already illustrated in a remarkable manner many of the most 

 obscure points of physical science, and promise to be productive of results 

 not inferior to any which have been reached since the days of Newton. 

 About twelve years ago, Mr. Joule demonstrated that the mechanical power 

 expended in overcoming the friction of any machine produces an amount of 

 heat of equivalent value to the power expended, so that, if this heat could be 

 employed again in an engine which worked without waste or loss, it would 

 exactly reproduce the power which had been expended in generating it. It 

 is obvious that as heat is producible by a machine without any waste of its 

 own substance, or is producible in water by agitation without the quantity of 

 water being diminished, heat cannot be a material substance, and both heat 

 and light are produced by vibrations similar to those which produce sound. 

 The steam generated in a boiler, when condensed by cold water, as is done ha 

 a condensing engine, produces a certain quantity of warm water; but a given 

 quantity of steam thus condensed wih 1 not produce the same temperature in 

 the water which has accomplished the condensation, if such steam has been 

 employed to work an engine, as it will produce if it has not been employed to 

 generate power. For, as power is equivalent to heat, the steam which is 

 employed to generate power would, unless there were a reduced temperature 



