TRANSACTIONS OF SECTION A. 553 



different values of the electric and liquid currents, the values in each case being 

 adjusted to give the same rise of temperature, it is clear that the temperature 

 distribution, and therefore the external loss of heat, will be very nearly the same. 

 The total loss can be reduced to two or three per cent, of the heat supply on a rise 

 of temperature of 10° C, and the residual differences in any set of observations are 

 but a small fraction of the total loss, and are easily corrected. 



We have so far applied the method only to the cases of water and mercury, 

 which present most interest. There is no difficulty, however, in extending the 

 method to the case of other liquids. We have made special arrangements for 

 applying the method to the determination of the variation of the specific heat with 

 temperature, for which purpose it is peculiarly suited, and was, in fact, originally 

 devised. The apparatus may be inspected at the McDonald Physics Building. 

 The essential parts were exhibited at the meeting. 



In applying the method to water we have found no difficulty in obtaining 

 steady readings over the range 0° to 50°, and we hope to extend the result to 75°. 

 Special arrangements, which have proved perfectly effective, are made to avoid 

 loss by evaporation. 



The results of the observations cannot as yet be published, as they are not 

 sufficiently numerous to merit attention, and still require the application of certain 

 final coiTections. The variation to be measured is so small that many of these 

 corrections may considerably alter the result. 



3. On the Behaviour of Argon in XRay Tubes. By H. L. Callendae, M.A., 

 F.R S., Professor of Physics, and N. N. Evans, M.A.Sc, Lecturer in 

 Chemistry, of McGill University, Montreal. 



In continuation of some experiments made by Professor Callendar in the early 

 part of 1896, the authors have studied the behaviour of argon and some other 

 gases in X Ray tubes of various types. The phenomena presented by a tube 

 filled with carefully dried and purified argon are in many respects peculiar. Under 

 certain conditions the gas appears to be absorbed with extreme rapidity, and with 

 intense sputtering and heating of the kathode. The phenomena appear to depend 

 on the complete elimination of hydrogen from the electrodes, as well as on the 

 degree of vacuum in the tube and the intensity of the current. From experiments 

 on other gases the authors conclude that hydrogen is the most suitable gas for 

 X Ray tubes, and that as a rule the residual gas present is hydrogen. It is possible 

 that the observed absorption of the argon is apparent merely, and corresponds to a 

 sudden increase of the resistance of the tube at a certain stage of the exhaustion, 

 and not to an actual disappearance of the gas. 



4. On the Fuel Supply and the Air Supply of tlie Earth. 

 By Lord Kelvin, F.R.S. 



All known fuel on the earth is probably residue of ancient vegetation. One ton 

 average fuel takes three tons oxygen to burn it, and therefore its vegetable origin, 

 decomposing carbonic acid and water by power of sunlight, gave three tons oxygen 

 to our atmosphere. Every square metre of earth's surface bears ten tons of air, of 

 which two tons is oxygen. The whole surface is 126 thousand millions of acres, or 

 610 million millions of square metres. Hence there is not more than 340 million 

 million tons of fuel on the earth, and this is probably the exact amount, because 

 probably all the oxygen in our atmosphere came from primeval vegetation. 



The surely available coal supply of England and Scotland was estimated by 

 the Coal Supply Commissiou of 1S71, which included Sir Roderick Murchison and 

 Sir Andrew Ramsay among its members, as being 146 thousand million tons. 

 This is approximately six-tenths of a ton per square metre of area of Great Britain. 

 To burn it all would take one and eight-tenths of a ton of oxygen, or within two- 



