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XI. On Thermal Radiation in Absolute Measured 
By J. T. Bottomley, M.A., D.Sc., F.R.S. 
Received and Read June 16, 1892. 
[Plates 17, 18.] 
In 1884t and in 1887]; I had the honour of submitting to the Boyal Society the 
results of certain experimental determinations of thermal emission in absolute measure. 
In these experiments metallic wires heated by an electric current were used. Much 
remains to be done by the methods and with the apparatus then employed; and I 
* [Since this paper was written, and since it was accepted by the Royal Society, a paper has appeared 
in the ‘Philosophical Transactions,’ 1893, A., vol. 183, by Professor W. E. Ayrton, F.R.S., and Mr. H. 
Kilgour, “ On Thermal Emissivity of Thin Wires.” In their preliminary remarks the authors, referring 
to my previous papers (among others), say : “But it was not part of these investigations to determine 
the change in the emissivity that is produced by change in the shape and size of the cooling body.” 
1 cannot avoid pointing out that this remark is wholly erroneous. My work on thermal emission, 
which was commenced on November 9, 1883, had altogether for its object, in the first instance, the 
finding of the effect of dimensions and form of the cooling body on the thermal emission; and the 
question of dimensions has never been lost sight of by me, and has, 1 think, been referred to in every 
paper 1 have published on this subject. 
In the ‘ Electrician’ for April 19,1884, there appeared a short account of my experiments, which were 
commenced as an experimental counterpart to a paper on “ The Efficiency of Clothing,” read by Lord 
Kelvin to the Royal Society of Edinburgh, on March 3, 1883. I found, however, that Professor G. 
Forbes had already (British Association, 1882, and ‘ Electrician,’ September, 1882) given important 
conclusions, derived theoretically, as to the effect of dimensions on the temperature of wires carrying the 
electric current. The theoretical conclusions of Professor G. Forbes were completely borne out by the 
results of my experiments; and those now given by Professor Ayrton and Mr. Kilgour agree. 
On June 17, 1884, 1 had the honour of reading a paper, which was wholly occupied with the effect of 
dimensions, before the Royal Society (‘ Proc. Roy. Soc.,’ No. 232, 1884). In the autumn of the same 
year I contributed a paper to the British Association on the same subject. These papers (of which the 
latter was published in ‘ Nature,’ September, 1884) contain a practical experimental investigation of the 
loss of heat from thin bare wires in air, so far as dimensions are concerned, as well as experimental results 
as to the effect of coverings of various kinds and different thicknesses. 
I have still a large number of results on these subjects hitherto unpublished; and as 1 have received, 
from the £4000 Scientific Fund, grants in aid of these researches, I am unwilling that there should be 
any misunderstanding in this matter.—March 2, 1893.] 
t ‘ Proceedings Royal Society, No. 232, 1884. 
t ‘Phil. Trans.,’ 1887. 
5.9.93 
