Chemistry and Physios. 277 



the strength of the photoelectric current are conditioned by the 

 concentration of the reactive gases at the zinc surface. The time 

 variation of the photoelectric current can be changed multi- 

 fariously by suitable combinations of the two processes constitut- 

 ing fatigue and recovery. 



(3) So long as ionization by collision does not enter as a factor, 

 the pressure of neutral gases has no influence on the magnitude of 

 the photoelectric effect. — PhysiJc. Zeitschr., No. 2, Feb., 1914, 

 pp. 65, 68. h. s. u. 



10. The Effect of Temperature on JL-ray Diffraction Patterns. 

 — DeBroglie immersed a cubical crystal of rock salt in liquid 

 nitrogen during an entire exposure with Rontgen rays and 

 obtained a photographic negative which was sensibly the same as 

 had been previously gotten with the same crystal at the ordinary 

 room temperature. In other words, the number, relative position, 

 and sharpness of the images appeared to be the same at both 

 temperatures. The same investigator tested a crystal of tour- 

 maline at a bright red heat and at the temperature of liquid air. 

 The only variation shown by the negatives seemed to be a very 

 slight decrease in intensity of the photographic impressions cor- 

 responding to the higher temperature. 



These results are in accord with the mathematical analysis of 

 P. Debije. It also comes out from this theory that as the tem- 

 perature of a crystal is raised the points close to the central image 

 are less influenced than the more remote images. Since the work 

 of deBroglie on the sharpness of the points at different tempera- 

 tures needed verification, the pi*oblem has been taken up anew 

 by M. v. Laue and J. Steph. van deb Lingen. The experi- 

 mental method consisted essentially in passing X-rays from the 

 same bulb simultaneously through two specimens taken from the 

 same crystal. Both pieces were subjected to as nearly identical 

 conditions as possible in all respects save one, namely, the one 

 crystalline fragment was heated in an electric oven while the 

 other was either kept at room temperature or plunged in liquid 

 aii\ Rock salt and mica were investigated from 320° C. and 

 400° C. respectively down to —190° C. The authors conclude 

 from their work that, at least qualitatively, the theory of Debije 

 on the influence of temperature is verified. — Le Radium, June, 

 1913, p. 186 ; Physik. Zeitschr., No. 2, p. 75, 1914. h. s. it. 



11. A Method of Measuring the Pressure Produced in the 

 Detonation of High Explosives or by the Impact of Pullets. — 

 Some interesting and instructive data relative to the preceding 

 title have been recently obtained by Bertram Hopkinson. The 

 apparatus used may be briefly described as follows : A cylindri- 

 cal steel rod is suspended after the fashion of a ballistic pendulum. 

 To one end of this rod a short segment of the same specimen of 

 steel and having the same cross-section is caused to adhere by 

 magnetic attraction. The ends of the rods which are in contact 

 have to be accurately plane and smooth. Beyond the short end- 

 piece an ordinary ballistic pendulum is hung up so as to catch the 



