54 MR J. Y. BUCHANAN ON THE 



§ 23. It was by an accident, which for the moment was annoying, that I found a very 

 simple and efficacious means of counteracting this loss of heat on the part of the liquid. 



At Edinburgh, in December 1902, I was making some observations on the specific 

 gravity of various saline solutions, and had got the temperature of the laboratory so 

 that 1 had no difficulty in carrying out the determinations without change of tempera- 

 ture of the liquid. In latitude 56° in December, even in clear weather, night begins 

 to fall early in the afternoon, and, in the middle of the work, I had to light the gas 

 in order to be able to continue it. The gas jet was fully a metre above the cylinder, 

 and the light which it gave, though sufficient, was far from brilliant. When I had 

 finished the series of the usual number, nine individual observations, and removed the 

 hydrometer, I took the temperature of the liquid, expecting to find that it had remained 

 sensibly constant as before ; but, instead of this, it showed a rise of several tenths of 

 a degree. As the gas had been burning for only a few minutes, it was impossible for 

 it, in the time, to raise the temperature of the air of the laboratory so that it, in its 

 turn, could raise that of the liquid in the cylijider by any sensible amount ; and, in 

 fact, on regarding the thermometer used for indicating the temperature of the air, it 

 was found that this had remained unchanged. For the moment I was perplexed ; the 

 shortness of the interval between the lighting of the gas jet and the production of the 

 heat-effect on the liquid in the cylinder situated at a considerable distance below it 

 puzzled me. However, after some reflection / 'perceived that it must he an effect of 

 radiation from the luminous flame of the gas jet, which, as soon as it was lighted, 

 dispatched its heat-rays in all directions and ivith the velocity of light. It was this 

 radiation that penetrated the cylinder and raised the temperature of the liquid in so 

 short a time ; and this eff"ect could be produced by no other agency. 



Further reflection showed me that the agency which can raise the temperature of 

 the liquid in this way can also prevent it falling, I gave eff"ect to this idea by attaching 

 a luminous gas lamp by an india-rubber tube to one of the gas cocks on the working 

 bench of the laboratory, and placed it between the cylinder and the window. The 

 gas burner was at a height above the table inferior to that of the top of the cylinder, 

 and the standard which carried it could be shifted towards or away from the cylinder 

 at will. 



It must be remembered that the provision of this gas flame was not for the purpose 

 of heating the air and raising or maintaining its temperature up to a certain degree ; it 

 was to supply the cylinder and liquid with heat, and that without warming the inter- 

 vening air ; and the heat so communicated from a distance was to be regulated so as 

 exactly to make good that which they were dissipating. 



As the combustion of the gas necessarily heated air which went upwards, it was 

 important to secure the supply of radiant heat with the least possible combustion of 

 gas. This was effected by reducing the flame so as to give the smallest possible flame 

 which was sufficiently luminous to furnish the necessary radiation at a distance which 

 was found to be convenient, generally from 50 to 75 centimetres. 



