302 Scientific Intelligence. 



its electro-magnetic energy may be transformed into waves wbich 

 are identical with light waves. Professor Thomson gives the 

 equations of condition for such a moving particle, and shows that 

 they lead to the conclusion that in the X-ray phenomena two 

 waves result from the electric impulses, one of which is a spheri- 

 cal wave and the other a plane wave. The dimensions of the plane 

 waves are extremely small. The X-ray effects are therefore pro- 

 duced at the surfaces where the electrified moving particles are 

 stopped. — Phil. Mag., February, 1898. j. t. 



10. Acoustic phenomena in the Electric Arc. — The initial resist- 

 ance of the voltaic arc is largely determined by the density of 

 the surrounding air. If a sound wave travels through the gase- 

 ous layer of the voltaic arc, there arise periodic changes in the 

 transitional resistance, and consequently similar periodic changes 

 result in the current strength. These changes can be studied in 

 neighboring telephone circuits. H. Th. Simon has made a care- 

 ful study of these phenomena, and makes a calculation of the 

 change of temperature produced by a sound wave passing through 

 the heated gas of the arc; and also of the change of pressure 

 which might result in the gas. Lord Rayleigh has estimated 

 that the least change of pressure which can produce an appreci- 

 able tone in ordinary air has the value Ap^G'lO -9 atmosphere. 

 Simon finds Ajo=9*10~ 5 atmosphere, and states that the discrep- 

 ancy probably arises from the presence of harmonics. Recent 

 experiments in the Jefferson Physical Laboratory with a large 

 storage battery show that the discharge of this battery through 

 vacuum tubes is accompanied by a high note which rises in pitch 

 as the resistance external to the tube is increased. — Wied. Ann., 

 No. 2, 1898, pp. 233-239. j. t. 



11. Time of vibration of very high notes. — It is well recognized 

 that the measurement of high notes is very difficult and Ant. 

 Appunn discusses the conditions for the investigation of such high 

 periods, and describes a series of .pipes constructed by him which 

 gave vibrations extending from 2500 vibrations a second to 50,000 

 per second. The length of the pipe which gave 50,000 per second 

 is 1*28 millimeters.— Wied. Ann., No. 2, 1898, pp. 409-416. 



J. T. 



12. Electrical excitation. — Many attempts have been made to 

 explain contact electricity by the laws of electrolysis, and thus 

 to connect it with the chemical and physical nature of the sub- 

 stances. Alfred Coehn discusses the various theories of ions and 

 ion concentration, and formulates the law that matter of higher 

 dielectric constants charge themselves positively by contact with 

 matter of lower dielectric constants. There are notable excep- 

 tions to this law. — Wied. Ann., No. 2, 1898, pp. 217-232. j. t. 



13. A Manual of Experiments in Physics; Laboratory Instruc- 

 tion for college classes; by Joseph S. Ames and William J. A. 

 Bliss. — This volume is a companion to the Theory of Physics, by 

 Professor Ames, which was noticed in the number of this Journal 

 for June, 1897. The long experience of the author as a teacher of 



