Proceedings. 



3i 



Professor Osborne Reynolds read the following 

 note " On Mr. HARTOG and Dr. Harker's Experiments 

 on the Latent Heat of Steam at 21 2° Fahr." : — 



" Since the publication of Regnault's experiments in 1848 

 there has been a general agreement as to the value of this 

 important constant. And no one, in the meantime, has 

 pointed out any source of error in Regnault's work. What- 

 ever may be the true value of this latent heat an agreement 

 as to the exact figure is of great importance. Otherwise 

 by the use of different figures results into which this con- 

 stant enters are thrown into discord. At the last meeting 

 of this Society Mr. Hartog brought forward results of some 

 very interesting experiments which show the latent heat to 

 be something like 2% less than that obtained by Regnault. 

 From the description, the experiments had evidently been 

 made with the greatest care and the results obtained from 

 different experiments are fairly consistent. Any source of 

 error must therefore be some general loss of heat which would 

 exercise the same effect on all the experiments. After 

 hearing the paper it occurred to me that such a loss of heat 

 must necesarily take place in the experiments from a cause 

 which appeared to have been overlooked by the author of 

 the paper. To this I now direct the attention of Mr. Hartog, 

 in the hope he may be able, by removing it, to bring his results 

 into accordance with Regnault's. The matter which seems 

 to me to have escaped the attention of Mr. Hartog is the 

 cooling effect on the interior tube of his apparatus, by which 

 the steam passed into the calorimeter, of external radiation 

 through the walls of his enclosing glass vessel. That this 

 would cause a loss is certain ; what this loss would be depends 

 on the temperature of the room and on the constants of 

 absorption of the surface of the interior tube and the glass 

 envelope." 



Messrs. Hartog and Harker replied to Professor 

 REYNOLDS, pointing out that the loss by radiation could 



