318 CARNEGIE INSTITUTION OF WASHINGTON. 



time after excitation, but the variety of short duration belongs to the 

 persistent type, as appears from the curves published by Waggoner 

 some years ago and from recent measurements of our own. 



The two varieties sometimes occur in contiguous veins. They are 

 indistinguishable during excitation by the iron spark, but upon break- 

 ing circuit the glow from one variety ceases immediately, while the 

 other continues to shine. Mr. D. T. Wilber, in the course of experi- 

 ments on the production of artificial willemite, has discovered the 

 cause of this difference. He finds the presence of manganese essential 

 to luminescence and that only those samples in which an abundance 

 of zinc oxide has been used in the preparation of the silicate exhibit 

 phosphorescence of long duration. The precise chemical relations 

 involved are under investigation. 



The Selective Radiation from Erbium Oxide. 



Dr. W. G. Mallory,* by way of completing his study of the selective 

 radiation from erbium oxide, has confirmed, by an independent 

 method, his previous determination of the striking fact that the 

 emission bands exceed in intensity the radiation of corresponding 

 wave-lengths from a black body of the same temperature, whereas 

 for other parts of the spectrum the black-body radiation greatly 

 exceeds the emission from the erbium oxide. 



If we accept the well-known definition that all radiation from a 

 substance in excess of that due to its temperature is to be regarded as 

 luminescence, the selective radiation from erbium oxide must be so 

 classed. The relations of its spectrum at 1,000° to the similar but not 

 identical spectrum produced by kathodo-excitation at room tempera- 

 ture and to the absorption spectrum have not yet been definitely deter- 

 mined. The very narrow absorption bands of the cold oxide occur in 

 groups which occupy the same regions of the spectrum as the broad 

 emission bands. The bands, both of emission and absorption, like those 

 in the spectra of the uranyl compounds and of luminescent substances 

 in general, form series having intervals of constant frequency. 



Studies in Magneto Striction. 



Dr. H. A. Pidgeon has completed his extended study of the Wiede- 

 mann and Joule effects in the magnetization of specimens of iron, 

 nickel, and cobalt, with special reference to the latter metal. The 

 results for pure cobalt differ materially from those obtained by other 

 observers working with unpure specimens and show a remarkable 

 similarity to the results for nickel. The twist produced by magnetiza- 

 tion is, however, much less in cobalt than in nickel. Certain eccen- 

 tricities of twist were observed in all specimens of the three metals. 

 These have been carefully studied and discussed. 



♦Since the writing of this report, new3 has been received of the sudden death of Dr. Mallory 

 at Obertin, Ohio. He had been for several years an instructor in Cornell University and had 

 recently been appointed to a professorship in physics at Oberlin College. Dr. Mallory was an 

 investigator of great promise and his attractive personaUty had endeared him to all his associates. 



