12 REPORT — 1853. 



temperature evolved by a small compression of a volume of air to the diminution of 

 temperature required to produce the same condensation under a constant pressure, 

 although originally intended to supply the data required by La Place in his peculiar 

 views on the transmission of sound, have also been employed ■with good effect in ad- 

 vancing the physics of gases with relation to temperature and mechanical force. 

 The ratio is in fact approximately an initial or differential ratio, which affords the 

 means of obtaining integrals that express simple laws of great importance. The ex- 

 periments of MM. Clement and Desormes have shown that the value of the ratio is 

 constant throughout a considerable range of temperature and density ; and Mr. Ivory 

 proved that it is constant under every change of density anq,temperature as long as 

 the laws of Marriotte and of Dalton and Gay-Lussac are maintained, or the air- 

 thermometer is an exact measure of heat (Phil. Mag., 1827). The mathematical 

 reasoning is much simplified by reckoning all temperatures from the zero of gaseous 

 tension. This zero by M. Rudberg's experiments, confirmed by Magnus and 

 Regnault, is situated at minus 461° upon Fahrenheit's scale, or minus 273°"89 Cent. 

 To save circumlocution, the author calls this the g temperature. This g temperature 

 of a gas is a definite and essential quality belonging to it, to be classed with its 

 density, volume and pressure. The author then proceeds to lay down the dif- 

 ferential equations, simplify their expressions by the results of experiments, and 

 state the final equations deduced by integration, from which he draws the following 

 conclusions: — 1. When air is compressed or dilated, the g temperature varies as 

 the cube root of the density, and the tension as the fourth power of the g tempera- 

 ture or cube root of the fourth power of the density. 2. The mechanical force 

 exerted by a given quantity of air while freely expanding from one density to 

 another is proportional to the difference of the cube roots of these densities, or to 

 the difference of their g temperatures, and the fall of temperature is proportional to 

 the force expended. 3. The mechanical force exerted upon a given quantity of air 

 while compressing it from one density to another is proportional to the difference of 

 the cube roots of these densities, or to the diffei-ence of their g temperatures, and the 

 rise of temperature is proportional to the force exerted. 4. The total force exerted 

 by a volume of air while expanding to infinity is equal to its tension acting through 

 three times its volume and the limit of its g temperature while thus expanding 

 in zero, and the same reasoning applies to compression. 5. The total mechanical 

 force exerted by a volume of air while expanding to infinity is proportional to its 

 G temperature. 6. A given quantity of air while expanding under a constant 

 pressure from one temperature to another exerts a mechanical force equivalent to 

 one-third the difference of temperature, and the quantity of heat required to change 

 the temperature of air under a constant pressure is four-thirds that required to effect 

 the same change of temperature with a constemt volume. Hence the author shows 

 that 1 lb. raised through 600 feet is the mechanical equivalent of 1° of heat applied 

 to 1 lb. of water; but if 0-267 be the specific heat of air under a constant pressure, 

 800 feet will be the number equivalent to 1° of heat, which is the number ex- 

 perimentally deduced by Mr. Joule. The author notes this as perhaps the simplest 

 example of that correlation of natural forces brought to light by the elegant researches 

 of Mr. Grove. 



Astronomy, Sea Currents, Depth of Sea. 



On the Currents of the Indian Seas. By George Buist, D.C.L., F.R.S. 



Water in motion is found to exercise two classes of agencies on the surface of 

 our globe : — first, a destroying one, levelling and throwing down continents and 

 mountains, transferring them to the depths of the ocean, either to be raised gra- 

 dually by those mysterious elevations now in operation or upheaved by violent 

 cataclysms, such as seem so frequently to have burst asunder the crust of the 

 earth ; and second, a destroying and reconstructing agency as in the case of the 

 Gulf-stream, redressing the equilibrium which it had just before disturbed — trans- 

 ferring the heat of the torrid zone to mitigate the rigour of the northern temperate 

 and polar regions, and eating away the roots by which the icebergs would have 

 remained for ever anchored, and so enabling them to transport themselves to cool 



