Intelligence and Miscellaneous Articles. 457 



medium attains its maximum conductive power, although it still 

 offers a readily appreciable resistance. 



The diminution of the elasticity of the different gases gradually 

 diminishes the difference between their conductive powers until, 

 when we arrive at a pressure of only 3 or 4 millimetres of mercury, 

 all the gases form equally good conductors. 



It is remarkable to see heat acting in the same manner as diminu- 

 tion of pressure in rendering the differences between the resistances 

 of the gases gradually less. But if heat diminishes the quantity of 

 matter lying in the way of the electric current in a given space, so 

 as to facilitate the passage of the electricity, it has also a very 

 distinct action of its own ; since at ordinary temperatures even the 

 most perfect vacuum that can be produced by air-pumps does not 

 possess conductive power ; whilst at a red heat the electricity can 

 pass through, even a condensed gas, where the mass submitted to 

 experiment is greater. 



It is easy to understand how complicated the comparison of the 

 resistances of gases must be, since their conductive power varies 

 with their temperature, their pressure, and the intensity of the cur- 

 rent. The results are also influenced by the nature of the metals 

 •employed in passing the electricity into the gas ; and it is necessary 

 to ascertain the resistance offered to its passage from the electrodes 

 into the gas in order to arrive at the actual resistance presented by 

 the latter. 



The author gives the following table of the conductive powers of 

 the gases employed in his experiments, at a red heat and at the 

 pressure of the atmosphere, with platinum electrodes. The resist- 

 ance of the air is regarded as unity, and the gases are arranged in 

 the order of their conducting power, commencing with the best 

 conductors. 



Hydrogen (resistance from 0*3 to 0'4 of that of the air, accord- 

 ing to the conditions of the experiments). 



Light carburetted hydrogen. 



Oxygen (resistance between 0*4 and 0*7). 



Chlorine (resistance not more than 0*92). 



Air. 



Protoxide of nitrogen 1 d;ffer ^ from ^ 



Nitrogen J 



Carbonic acid (resistance from 1*2 to 2*0). 

 Further details are given by the author in his memoir. — Comptes 

 Rendus, July 4, 1853, p. 20. 



ON THE CALCULUS OF OPERATIONS. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 I beg leave to correct the two following errors which occur in 

 my recent paper on the Calculus of Operations. 



In page 352, the expansion of (v + c) -1 ^D should be 



Phil Mag. S. 4. Vol. 6. No. 41, Dec, 1853. 2 H 



