744 Mr. H. E. Ives on the 



action. I have often been surprised that the connexion 

 between the two phenomena is not more general than it 

 appears to be. I do, however, think that there is a con- 

 siderable body of evidence in favour of the view that there 

 is an emission of electrons from hot conductors which is 

 independent of chemical action. 



I ought to add that the experiments of Pring and Parker 

 only support the theory very partially. The currents they 

 obtained at a high temperature are still about 100 times less 

 than those calculated above; but there is sufficient uncer- 

 tainty in the data to admit the possibility of such a difference 

 without vitiating the theory. The large variation of the 

 current with the pressure of the surrounding gas may be, I 

 think, an immaterial factor, unless the minimum currents 

 can be shown to be too small. The comparative absence of 

 increase of the emission with increasing temperature is a 

 more important consideration and calls for further investi- 

 gation. Experiments are now being instituted in this 

 laboratory which, 1 hope, will shed more light on this 

 phenomenon. 



Palmer Physical Laboratory, 

 Prin. eion, N.J. 



LXXV. Studies in the Photometry of Lights of Different 

 Colours. — III. Distortions in Spectral Luminosity Curves 

 produced by Variations in the Character of the Comparison 

 Standard and of the Surroundings of the Photometric Field. 

 By Herbert E. Ives *. 



A PREVIOUS paper in this series described spectral 

 luminosity curves obtained by the equality of bright- 

 ness and flicker photometers. The mean of the high 

 illumination values as obtained by five observers showed 

 close agreement between the two photometric methods, 

 although the relative positions of the equality of brightness 

 and flicker curves varied among the different individuals. 

 In the same paper attention was drawn to the fact that these 

 measurements covered only a special case, namely, that of 

 comparison of the spectral colours against a single compari- 

 son source — the unsaturated yellow of the carbon incandescent 

 lamp. Certain experiments there quoted raised the suspicion 

 that the luminosity curve obtained might be to some extent 

 a function of the colour and saturation of the comparison 

 standard due to the accentuation of colour by simultaneous 



* Comir.umcatad t>v the Author. 



