496 Scientific Intelligence. 



7. Excitement of Positive Rays by Ultra-violet Light. — The 

 origin of positive rays is still undecided. Riecke and Ewers 

 attribute them- to positively charged metal ions shot off from 

 the cathode metal. Gehrcke believes that they are due to the 

 light electric effect of the electric discharge on particles shot 

 out from the cathode. This higher electric effect results in a 

 redistribution of electrons, and the formation of positively 

 charged particles. W. Wien believes that a regeneration can 

 take place in a jar after an electric discharge has passed through 

 it and after the discharge has been submitted to the effect of a 

 magnetic field. H. Dembee has made an investigation of the 

 production of positive rays by means of ultra-violet light. By 

 means of the Wehnelt electrodes and the rays of a quartz quick- 

 silver lamp, he was able to excite the rays by a small difference 

 in potential. The experiments were carried out over a large 

 range of pressures. The lowest pressure was obtained by means 

 of Dewar's method of charcoal and liquid air, and extended from 

 0-00001 l mm to 0-000008 mra of mercury. The curves obtained in 

 the extreme vacuum show that what may be termed jostling 

 ionization does not appear, and therefore the observed positive 

 particles arise from something shot off from the cathode. The 

 author describes two species of positive rays due to the light 

 electric effect.— Ann. der Physik, No. 11, 1909, pp. 137-165. 



J. T. 



8. Electricity excited by the fall of Mercury through gases 

 upon the surfaces of metals. — This paper is of interest to meteor- 

 ologists and to those who hold to a belief in the theory of 

 contact electricity. The author, A. Becker, lets a line stream of 

 pure mercury fall through a chamber, filled with certain gases, 

 upon surfaces of different metals, and measures the electric 

 potential. His facts are not in contravention to the arrangement 

 in series of the contact difference of potential of various metals. — 

 Ann. der Physik, No. 10, 1909, pp. 909-940. j. t. 



9. Viscosity of Gases. — Experiments have been conducted 

 in the Jefferson Physical Laboratory lor several years by Dr. 

 J. L. Hogg on this subject. These experiments have led inci- 

 dentally to a comparison of the McLeod gauge and Maxwell's 

 disc method. The latter method appears to be capable of great 

 accuracy, and Dr. Hogg has evaluated the viscosity of the quartz 

 suspending fiber. Gy. Zemplen adopts, to avoid the viscosity of 

 the fiber, a small deflection of a hollow sphere moving in a con- 

 centric sphere. He shows the applicability of the formula which 

 he deduced. It was found that the friction coefficient of dry atmos- 

 pheric air was independent of the rotation velocity (228 seconds 

 to 22 seconds), and that it is greater in moist air in certain limits 

 than in dry air. — Ann. der Physik, No. 10, 1909, pp. 869-908. 



J. T. 



