320 Mr Meikle on fimlhig the Deiv-point, S^^c. 



fessedly to shew the probabihty of a combination of lines being^ 

 found which should serve for the construction of a convenient 

 practical scale ; and from delineating two pretty large hyperbo- 

 las, I find that, by making the distances of the parallels for de- 

 grees of temperature to decrease a little in the lower part of the 

 figure, the results everywhere come very near those of the table, 

 except in a few cases which, like the above example, ran never 

 occur. I have also found that straight lines might be used in 

 place of the hyperbolas, by making the divisions for degrees of 

 temperature to decrease both ways from the 54th degree ; and 

 that by putting a curve, which would need to be one of double 

 curvature, in place of the asymptote, straight lines with almost 

 equal divisions might be got to answer in place of hvpcrbolas. 

 But perhaps a medium between these different constructions 

 would be the preferable one ; namely, to curve slightly all the 

 lines but the parallels of temperature, and to use intervals some- 

 what unequal between the latter. It is evident that if any sort 

 of curves were substituted for these parallels, a straight line or 

 ruler would not be sufficient to lay across this scheme; but 

 where a ruler is not at hand, its place may be very well supplied 

 by stretching a fine thread. 



The author of the article above quoted seems to have laid 

 hold of very apocryphal authorities for the specific heat of air 

 varying as the square root of the pressure. As for the experi- 

 ments of Desormes and Clement, to which he alludes, I do not 

 see how they warrant any thing of the sort. These distin- 

 guished chemists having inclosed air in a glass globe, placed it 

 in an empty trough, which they next filled with hot water, and 

 assumed that the specific heat of the air was exactly proportion- 

 al to the time which it and the globe took to acquire the same 

 temperature with the water; whereas, for aught that is known 

 to the contrary, the specific heat might follow some other power 

 or root, or some very complex function of the time. Nor do 

 they make any allowance for the share which the mass or mat- 

 ter of this globe, which far exceeded that of the included air, 

 had in protracting the time ; or for the different mobilities, and 

 consequently different conducting powers of different gases, or 

 of the same gas at different pressures. Thus, when the globe 

 was filled with hydrogen, it was probably from the extreme mo- 



