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DR. J. T. BOTTOMLEY AND MR. F. A. KING ON THERMAL 
direction indicated by the new facilities given to us, which both greatly extended the 
limits governing the enquiry, and also made it possible to obtain determinations, in 
absolute measure, of thermal radiation between bodies at extremely low temperatures. 
It seemed specially interesting, for example, to determine, in absolute measure, the 
radiation under given circumstances from a body at, say, ordinary atmospheric 
temperature, to an enclosure at a temperature which may perhaps approximate to 
that of space. With the exception of some preliminary results, which were 
communicated 18 months ago to the British Association, nothing of the kind has 
been published, so far as we are aware. 
3. The main object of the present paper is to give an account of this research. 
We have also, however, made an endeavour to sum up, and bring into co-relation, the 
results of earlier experiments, made under various circumstances, with forms of 
apparatus differing widely from each other, with different radiating surfaces and 
different enclosures, or sometimes with the same apparatus after it has been dis¬ 
mantled and re-erected. Finally, we have made an attempt to apply the law of 
Stefan to the results, in order to obtain some idea as to how far the conditions under 
which it holds have been realised in these experiments. 
Description of the Apparatus Employed. 
4. Although the apparatus used has already been described in former papers, a 
short description of it here will probably be of advantage, particularly as it was 
