854 



SCIENCE 



[N. S. Vol. XXX. No. 780 



About the same time Daniel Berthelot* pub- 

 lished a statement concerning the changes 

 ■which specimens of certain minerals, placed 

 by Marcellin Berthelot in November, 1906, in 

 the neighborhood of radiferous barium chlo- 

 ride, had undergone in a years' time. It was 

 found that a colorless quartz from la Gar- 

 dette and a white, cleavable fluorspar were 

 unchanged; that a violet, amethystine quartz 

 (containing manganese) from Uruguay, which 

 had been previously decolorized by heating, 

 was recolored; and that a violet fluorspar 

 from Weardale (Durham) had behaved simi- 

 larly. 



Later Bordas'^ observed that the coloration 

 of crystallized alumina by exposure to radium 

 bromide is not due to the action of the a- 

 rays, since these were absorbed by the glass 

 envelope containing the bromide; but that the 

 y-rays are operative in this respect, for color- 

 less corundum becomes distinctly yeUow after 

 forty minutes, and topaz colored after several 

 hours' exposure to the action of the Eontgen 

 rays, and these rays are analogous to the 

 y-rays of radium. 



On April 5, 1909, the writer received sev- 

 eral crystals of ruby from W. P. Dewey, of 

 Los Angeles, Cal. Two of these specimens 

 were placed in radium chloride of 7,000 ac- 

 tivity; one in a tube containing radium 

 chloride of 7,000 activity, in order that the 

 emanation would act upon it; and several in 

 a box containing radium of the same activity. 

 These were then set aside in the dark, and 

 examined recently after six months' exposure. 

 No change in color was observed, and the 

 specimens were entirely unaffected. 



Chas. Baskeeville 

 College of the City of New Yobk, 

 November 12, 1909 



demonstrations of electrical oscillations 



The production of high-frequency oscilla- 

 tions from arc or spark has become such 

 a simple matter that the use of the experi- 



* Compt. rend., 145, 818. 

 ' Compt. rend., 145, 874. 



ments described by Professor Huff in Science 

 for November 12 is strongly to be recom- 

 mended, especially as demonstrations before 

 classes in alternating currents. With ex- 

 tremely simple means one can exhibit to an 

 almost extravagant degree some of the eiiects 

 of alternating currents which at commercial 

 frequencies either do not appear at all, or 

 only with the aid of more costly apparatus. 



In this connection the following notes may 

 be of service: 



1. Steadier and more rapid oscillations are 

 attainable with the metallic arc than between 

 carbon electrodes. The iron are in free air 

 gives good oscillations, especially when ca- 

 pacity and self-inductance are so adjusted 

 that the note is a shrill squeak. 



2. Many commercial condensers show well 

 the phenomenon of the " musical capacity," 

 i. e., the production of a musical note syn- 

 chronous with that in the arc. The arc 

 should be placed at a considerable distance 

 from the condenser. 



3. Simon's " speaking arc " is shown with 

 a pair of flaming arc carbons and 220-volt 

 supply, making the arc as long as possible. 

 Connect in parallel with the arc a capacity of 

 from 1 to 5 m.f. and the secondary of a small 

 transformer. The transformer primary is in 

 series with a battery and telephone trans- 

 mitter capable of carrying an ampere. After 

 a little experimentation the arc can be made 

 to reproduce sounds audible throughout a 

 large room. 



4. Should the arc go out accidentally, it 

 may be found that the transformer continues 

 to reproduce the sounds, illustrating the 

 " speaking transformer." 



5. Some effects at much higher frequencies 

 can be shown by means of the type of dis- 

 charge recently described by the author.' 

 When a discharge at about one tenth of an 

 ampere is passed between metallic terminals 

 in illuminating gas, or better in a mixture of 

 hydrogen and acetone vapor, oscillations of 

 the order of a million per second are generated 

 without the aid of capacity or self-inductance 



'Am. Jour. 8ci., September, 1909, p. 239. Phys. 

 Zeitsohr., September 15, 1909, p. 623. 



