Geology and Mineralogy. 247 



arrangement thin cylinders of various metals enclosed a portion 

 of the wire upon which the electrical waves were excited. These 

 thin cylinders pi*otected the inner wire from electrical disturb- 

 ances. Thin deposits of silver on glass cylinders which allowed 

 light to be seen through them did not entirely shield the inner 

 wire. When the thickness of the silver layer increased to only 

 yi-Q of a millimeter all sparks disappeared in the spark detector, 

 showing that the electrical disturbance was entirely on the sur- 

 face of the conductor. Instead of saying, therefore, that electrical 

 waves are propagated through the wires, we should say that they 

 glide along the surface of the wire. Further experiments are 

 added which conclusively show that the electrical waves are con- 

 fined to the surface of the conductor, and that they are greatly 

 influenced upon two neighboring conductors by the character of 

 the intervening space and by surrounding objects. Hertz con-^ 

 eludes with the observation that, according to former ideas, he 

 classed among conductors those substances which allowed the 

 passage of electricity, and among insulators those that did not 

 permit this passage. According to the new interpretation of 

 electrical oscillations or waves, all electrical waves are propa- 

 gated through insulators, and good conductors oppose the quick 

 oscillations of these waves. The terms conductors and insulators 

 therefore should change places. — Ann. der Physik und Chemie, 

 No. 7, 1889, pp. 395-408. J. T. 



2. Disintegration of Surfaces by means of the Ultra Violet 

 rays. — Philipp K. Lenard and Max Wolf, by means of Helm- 

 holtz's modification of Aitken's apparatus (Wied. Ann., xxxii, p. 1, 

 1887), show that the ultra violet rays exert a remarkable effect in 

 producing dust from metallic surfaces. As a source of light sparks 

 from a Ruhmkorf coil were used, it having been shown that 

 these sparks are richer in violet rays than other sources of light, 

 and have the advantage of not causing heat and are therefore to 

 be preferred to the voltaic arc formed between carbon and zinc, 

 which has been used by some observers. The presence of the 

 dust was shown by the vapor produced in a suddenly exhausted 

 receiver according to the method of Aitken, and also by the col- 

 oration of a jet of steam. The latter method Helmholtz had 

 shown to be very sensitive, showing by changes of color the pres- 

 ence of metallic dust. All metals examined when negatively 

 electrified showed metallic dust under the influence of ultra violet 

 rays. Quartz and gypsum also showed disintegration. Fluids 

 also when negatively electrified gave forth finely divided par- 

 ticles. — Ann. der Physik und Chemie, No. 7, 1889, pp. 443-456. 



J. T. 



II. Geology and Minekalogy. 



1. Eruption of Baldai-san, in northern Japan, on July 15, 

 1888. — This eruption, noticed in vol. xxxvi of this Journal, is 

 reported on by Mr. Y. Kikuchi in the third volume of the Col- 

 lege of Science Journal of the Imperial University, of Tokyo. 

 The facts were briefly these : 



