440 Mr. J. Joly. On the [Nov. 20, 



the electrodes of all dust, and seems to dispel all dnst from the gas 

 through which the discharge occurs. It is well known that an 

 electric discharge in a vessel of air has the effect of clearing out of the 

 air all the particles that serve as nuclei for the condensation of water ; 

 and we made several experiments with a view to determine whether a 

 similar effect was produced on the dust in our tubes. The gas from 

 the sparking tube was carried through a glass globe, and so on to the 

 jet where it was burned ; a wire connected with one pole of a Voss or 

 Wimshurst electric machine projected into the interior of the globe, 

 and a patch of tinfoil on the outside of the globe was connected with 

 the other pole of the electric machine. So long as the Voss machine 

 was not worked, the gas carried the dust from the sparking tube 

 through the globe, and it was seen in the spectrum of the flame, or 

 simply in the colour of the flame when lithium was one of the elec- 

 trodes ; but, on working the machine so as to produce a silent dis- 

 charge inside the globe, the flame, in one or two seconds, suddenly 

 ceased to show the spectrum of the dust, and in the case of the 

 lithium lost its red colour. When the machine was no longer worked, 

 the spectrum or colour speedily reappeared, to vanish again suddenly 

 when the machine was started afresh. When a narrow tube, with a 

 piece of tinfoil outside and a wire inside, was substituted for the 

 globe, the like results ensued. 



It appears, then, not only that dust, however fine, suspended in a 

 gas will not act like gaseous matter in becoming luminous with its 

 characteristic spectrum in an electric discharge, but that it is 

 driven with extraordinary rapidity out of the course of the discharge. 

 If, then, the spectrum of the aurora be due, not to the ordinary con- 

 stituents of our atmosphere, but to adventitious matter from planetary 

 space, we conclude that such matter must be in, or must be brought 

 into, the gaseous state, or at least have its properties entirely altered 

 from those it possesses at ordinary temperatures, before it becomes 

 luminous in the electric discharge. 



III. "On the Specific Heats of Gases at Constant Volume. 

 Part I. Air, Carbon Dioxide, and Hydrogen." By J. JOLY, 

 M.A., B.E., Assistant to the Professor of Civil Engineering, 

 Trinity College, Dublin. Communicated by Professor 

 FITZGERALD, M.A., F.R.S., F.T.C.D. Received September 2, 

 1890. 



(Abstract.) 



In this first notice the specific heats, at constant volumes, of air, 

 carbon dioxide, and hydrogen are treated over pressures ranging 

 from 7 to 25 atmospheres. The range of temperature is not sensibly 



