Intelligence and Miscellaneous Articles. 77 



night as by day at a distance of one league ; and he states that the 

 same phenomenon has been observed near every waterfall in 

 Europe. And although Humboldt gave another explanation*, 

 which was very reasonable when applied to the particular case at 

 Orinoco t, yet it must be admitted that the circumstances were such 

 as would cause great upward refraction ; and hence there can be 

 but little doubt that refraction had a good deal to do with the 

 diminution of the sound by day. 



In fact if this refraction of sound exists, then, according to 

 Mr. Grlaisher's observations, it must be seldom that we can hear 

 distant sounds with any thing like their full distinctness, particu- 

 larly by day ; and any elevation in the observer or the source of 

 the sound above the intervening ground will increase this range 

 and distinctness, as will also a gentle wind, which brings the 

 sound down and so counteracts the effect of refraction. And 

 hence we have an explanation of the surprising distances to which 

 sounds can sometimes be heard, particularly the explosion of me- 

 teors, as well as a reason for the custom of elevating church-bells 

 and sounds to be heard at great distances. — September 1874.] 



XL Intelligence and Miscellaneous Articles. 



ON THE ACTION OF MAGNETS ON RAREFIED GASES IN CAPILLARY 

 TUBES RENDERED LUMINOUS BY AN INDUCED CURRENT. BY 

 J. CHAUTARD. 



r jPHE spectral modifications produced by the action of magnets 

 * on the light of an induced current traversing rarefied gases 

 are subject to very complex laws ; and it is only possible to formu- 

 late them after varied and long-continued experiments. M. Treve, 

 in a Note published in the Comjptes Rendus (Jan. 3, 1870), after in- 

 dicating some facts bearing on this class of phenomena, concluded 

 in these terms — " coloration and decoloration of the gases under 

 the action of magnetism, in the capillary parts of the tubes contain- 

 ing them;" but the experiments of the accomplished officer were 

 not very numerous, they were made on only a few gases, and ap- 

 peared to be only indirectly connected with the researches he had 

 undertaken. The subject seemed to me sufficiently interesting to 



* " That the sun acts upon the propagation and intensity of sound by the 

 obstacles met in currents of air of different density, and by the partial undula- 

 tions of the atmosphere arising from unequal heating of different parts of the 



soil During the day there is a sudden interruption of density wherever 



small streamlets of air of a high temperature rise over parts of the soil unequally 

 heated. The sonorous undulations are divided, as the rays of light are refracted 

 wherever strata of air of unequal density are contiguous. The propagation of 

 sound is altered when a stratum of hydrogen gas is made to rise over a stratum 

 of atmospheric air in a tube closed at one end ; and M. Biot has well explained, 

 by the interposition of bubbles of carbonic acid gas, why a glass filled with cham- 

 pagne is not sonorous so long as that gas is evolved and passing through the strata 

 of the liquid." — Humboldt's Travels, Bonn's Series, vol. ii. p. 264. 



t The sounds proceeded over a plane covered with rank vegetation interspersed 

 with black rocks. These latter attained a very considerable elevation of tem- 

 perature under the effects of the tropical sun, as much as 48° C, while the air 

 was only 28°; and hence over each rock there would be a column of hot air 

 ascending. 



