406 SCIENTIFIC RECORD FOR 18S-2. 



IV. — rHYSICAL QUESTIONS. 



B. J. Hopkins suggests tliat specimens of the atmospheric dust that 

 are to be examined with reference to the question of the presence of 

 meteor dust should be collected regularly by apparatus attached to 

 properly constructed captive balloons, so as to avoid the presence of a 

 mass of dust of terrestrial origin. {Nature, xxv, p. 339.) 



Professor Schuster, in the report of the committee on meteoric dust, 

 says that the occurrence of magnetic particles in dust, especially that 

 discovered by Tissandier in the snows of Mont Blanc, is explicable only 

 on one of three hypotheses : First, the particles may be of volcanic origin ; 

 second, they may come from the smoke of our own chimneys; third, 

 they may have a cosmic origin. The latter hypothesis is strongly fa- 

 vored by the consideration that the iron particles issuing from our chim- 

 neys contain neither nickel nor cobalt, while these metals do exist in 

 the microscopic magnetic particles of atmospheric dust. Schuster finds 

 that the sand near the great pyramids and the desert of liajpootana, 

 and also from the Isile mud near the canal, all contain these rare metals. 

 As regards their origin, he concludes that at high elevations the pro- 

 portion of oxygen in the atmosphere is very small, and that inasmuch 

 as there is still a line in the aurora spectrum that has not been recog- 

 nized as belonging to any known substance, he is convinced that it is 

 due to some unknown gas of very small density. It is the contact of 

 the meteors with this gas that fills the upper regions with meteoric dust 

 which first makes it possible for the aurora to exist at those elevations, 

 and afterwards, settling towards the earth, is brought down by the 

 snow and rain to the surface. {Nature, xxvi, p. 488.) 



Prof. F. A. Abel, in a lecture before the Eoyal Institution on atmos- 

 pheric dust, shows the various dangers to which the hum.an race are 

 thereby subjected. Passing by the microscopic germs of disease float- 

 ing in the air, he confined his attention to the larger dust particles, for 

 instance, those of coal dust in mines, the sulphur dust in powder mills, 

 finely divided cotton fibers in cotton mills, and the dust in flour and 

 rice mills ; all these and many other forms of dust, when sufliciently 

 abundant in the air, make a dangerously explosive mixture, and there 

 can be no doubt many explosions in coal mines have been due to dust- 

 laden air rather than fire-damp. The lecturer paid special attention 

 to the suggestion of methods for the avoidance of danger from these 

 sources. {Nature, xxvi, p. 20.) 



Miintz and Aubin have observed the relative proportion of carbonic 

 acid in the upper and lower regions of the atmosphere thej' observed 

 on the Pic du Midi and the plain around — the difference seems inap- 

 preciable. {Comptes liendus, Paris, November 14, 1881.) 



Dumas communicates to the Paris Academy some observations on 

 the amount of carbonic acid in the atmosphere. After noticing the 

 defects of several methods of measurement, lie commends the exactness 



