METEORIC DUSTS, N.S.W. 275 



meteoric inflow unaccompanied by visual phenomena in the 

 form of "shooting stars," which would make its advent 

 visible to all. Admitting then the possibility of meteoric 

 influence we must consider it to be nevertheless extremely 

 improbable. There is another cause, which I understand 

 has been suggested by Mr. Norman Lockyer — though I 

 have not seen his article — that of volcanic dust." 



Prof. Langley then speaks of the dust present in the 

 apparently clear air of the upper parts of Mt. Etna, sur- 

 rounded by snow fields and deserts of black lava, yet the 

 telescope showed that the air was filled with minute dust 

 particles, which evidently had no relation to the local sur- 

 roundings, but apparently formed a portion of an envelope 

 common to the whole earth. 



In 1881 Prof. Langley was on Mt. Whitney, Southern 

 California, with an expedition from the Allegheny Obser- 

 vatory, where from a height of 15,000 feet they looked 

 down upon a kind of level dust ocean, invisible from below, 

 but whose depth was six to seven thousand feet. The 

 colour of the light reflected from this dust was clearly red 

 and it stretched in every direction as far as the eye could 

 reach, although there was no special wind or local cause 

 for it. It was evidently like the dust seen in mid ocean 

 from the Peak of Teneriffe ; something present all the time 

 and a permanent ingredient of the earth's atmosphere." 



Mr. Clarence King, Director of the U. S. Geological 

 Survey, thought that this upper dust was probably due to 

 the "loess" of China having been borne across the Pacific 

 and quarter of the way round the world. We were at the 

 top of the continent and the air which swept by us was 

 unmingled with that of the lower regions of the earth's 

 surface. Even at that great elevation the dust was per- 

 petually present in the air, and I became confirmed in the 

 opinion that there is a permanent dust shell enclosing the 



