Influence of Radiation on the Transmission of Heat. 243 



the horizontal axis of the diffraction pattern these subsidiary 

 spectra vanished; so that the absence of all components, 

 except the second and third, from the aperture-curve could 

 be inferred from the observation. 



It will be evident from what has already been said that 

 confusion arises when the point-source is replaced by a linear 

 one ; and this is what theory would lead us to expect. In a 

 diffraction-grating, as usually constructed, where all the lines 

 are of equal length, the spectra are of the same character 

 whether the source be elongated, or not, in the vertical 

 direction ; but it is otherwise here. The inadmissibility of a 

 linear source and the necessity for limiting the observation to 

 the axis seriously diminish the prospect of making this method 

 a practical one for the discovery of unknown periods in curves 

 registering meteorological or similar phenomena ; but the fact 

 that the analysis can be made at all in this way, without an} 

 calculation, is at least curious and instructive. 



It may be added that a similar method is applicable when 

 the phenomena to be analysed occur discontinuously. Thus 

 if the occurrence of earthquakes be recorded by ruling fine 

 vertical lines of given length with abscissae proportional to 

 time, so as to constitute a grating, the positions of the bright 

 places in the resulting spectrum will represent the periodicities 

 that may be present in the time distribution of the earthquakes. 

 And in this case the use of a linear source of light, from which 

 to form the spectrum, is admissible. 

 Terlino- Place, Witham. 



XXII. The Influence of Radiation on the Transmission of Heat. 

 By Arthur Schuster, F.R.S* 



[Plate II.] 



1. rjlHE laws of conduction of heat have been studied in 

 JL detail, and something has been done to trace the 

 influence of convection on the distribution of temperature ; 

 but the effects of radiation on the transmission of heat 

 through partially transparent bodies have been almost entirely 

 neglected. With the solitary exception of a paper by 

 Professor R. A. Sampson f, with which I became acquainted 

 after the greater portion of the results of the present inves- 

 tigation had been worked out, I know of no serious attempt 

 to deal with this problem. 



* Communicated by the Author, 

 f Memoirs of the Royal Astronomical Society, vol. li. 

 R2 



