January 13, 1922] 



SCIENCE 



53 



SPECIAL ARTICLES 



EMISSION BANDS OF ERBIUM OXIDE: A 

 CONFIRMATION 



In a paper by the late Professor W. G. Mal- 

 lory 1, published in 1919, a photometric study 

 of the spectrum of glowing erbium oxide was 

 described. When the oxide was heated to 1,000 

 degrees Centigrade three regions, in which the 

 principal emission bands of this interesting 

 spectrum are situated, were found to be 

 brighter than the corresponding wave-lengths 

 in the spectrum of an ideal black body at the 

 same temperature; the red region slightly 

 brighter and the green and blue several times 

 brighter. 



This result has been questioned, although 

 not so far as we are aware in print, on the 

 ground that no radiator can exceed the emis- 

 sion of a black body of the same temperature. 



In other words it is held, as a matter of thermo- 

 dynamics, that the brightest regions in the spec- 

 trum of a selective radiator may reach, but 

 never reach beyond, the envelope which en- 

 closes the area representing the distribution of 

 radiation from a black body of the same tem- 

 perature. The explanation offered in Mallory's 

 paper suggests luminescence of the incandes- 



1 Mallory: Physical Seview (2) XIV p. 54. 



cent oxide superimposed upon the ordinary 

 radiation due to temperature. 



In the course of studies noAV in progress, in 

 which an altogether different method is used ^, 

 we find many instances of luminescence super- 

 imposed upon the ordinary temperature radia- 

 tion of incandescent oxides and producing in- 

 tensities greatly in excess of those of the same 

 regions in the spectrum of the black body. 

 Moreover in the case of erbium oxide we iOnd 

 these excesses in the same regions and at the 

 precise temperature designated by Mallory. 



The accompanying figure is from our data 

 for the three regions in question and covers 

 temperatures slightly below 1000°. Intensi- 

 ties are in terms of the brightness of the cor- 

 responding radiation from a black body of the 

 same temperature as the oxide and are thus 

 directly comparable with Mallory's results. 



While the sample of erbium oxide used by 

 us did not happen to be quite as actively lumi- 

 nescent as in Mallory's experiment the effect 

 is there and is of the same order. His observa- 

 tions are corroborated in every essential re- 



E. L. Nichols 

 H. L. Howes 



Physical Labokatort or Coenell TJNrvEEsiTY 

 October, 1921 



LABORATORY DETERMINATIONS OF DIP 

 AND STRIKE 



The writer has observed that many geology 

 students are unable to make correct determina- 

 tions of dip and strike. This weakness seems 

 to be due to the difliculties of presenting the 

 subject in the field, to lack of sufficient labora- 

 tory training before entering the field, and 

 especially to lack of suitable apparatus. In 

 the field, the determination of dip and strike 

 appeals to the student as a very minor and 

 uninteresting detail in comparison with the 

 other geological features to which his attention 

 is called. Furthermore, the rock surfaces are 

 usually so irregular that the instructor can not 

 make a very close check of the student's read- 

 ings. In the laboratory, the tilted drawing 

 boards, table tops, or rock slabs commonly 

 used are not very efficient because they often 

 possess straight edges indicating the line of 

 strike and are usually so insecurely fastened 



2 To be described in a forthcoming paper. 



