656 Intelligence and Miscellaneous Articles. 



know, from a recent discovery, that it forms in combination with 

 manganese a strongly magnetic substance the special property of 

 which is that the magnetic quality is first brought into evidence 

 (in a similar manner to that for several other existing combinations, 

 of non-magnetic substances) in the heated state at temperatures 

 between 2000° and 2300° C. 



This fact, so extraordinary and surprising when compared with 

 all hitherto ascertained results, appears to me to be worthy of 

 attention, especially by geophysieists. 



The question arises : If radioactive processes constitute the 

 source of the internal heat of our planet, to what extent may they 

 at the same time determine its magnetic state ? 



Except this more omnipresent radioactive heat there are local 

 sources of increased temperature, the principal one amongst them 

 caused, as it seems to me, by friction and pressure of a few inces- 

 santly moving enormous parts of our planet's crust against each- 

 other ; so that here and there in the contact-regions matter is- 

 liquefied and, sometimes, by the same reason, pushed through 

 the earth's surface, thus showing us the what we call volcanic 

 phenomena. 



Rotterdam, February 13, 1909. 



THE GRATING SPECTRUM OF THE RADIUM EMANATION. 

 To the Editors of the Philosophical Magazine. 



Gentlemen, — 

 Pkof. E. B. Eeost has called my attention to his publication of a 

 portion of the secondary hydrogen spectrum in the ' Astrophysical 

 Journal,' vol. xvi. p. 104 (1902), with reference to my paper on 

 " The Grating Spectrum of the Radium Emanation," published in 

 the January Number of the Phil. Mag. Pro in Prof. Frost's list it 

 appears that, in addition to the hydrogen lines already marked, the 

 lour lines which were marked as not having been seen in the 

 prism spectrum are due to the secondary spectrum of hydrogen* 

 These four lines were not observed in the prism spectrum, although 

 they were at more than resolvable distance from other lines, audit 

 was therefore probable that they were due to hydrogen which it 

 had not been possible to remove so completely in the experiments 

 for the grating photographs. Not being aware of Prof. Frost's 

 determination at low pressures, however, I had not been able to 

 trace these lines to hydrogen from the determinations of Hasselberg 

 and Ames. 



I should like to take this opportunity of correcting a printers' 

 omission of a footnote to the effect that the strong emanation line 

 4308-3 in the prism spectrum was masked in the grating photo- 

 graphs by the strong iron line of the comparison spectrum at 

 4307*96 (G in the solar spectrum), and its wave-length could not 

 be measured more accurately. 



Tours truly, 

 Physikahsches Institut, T. Royds. 



Tubingen, Germany. 



March 3, 1909. 



