PROGEESS OF MICEOSCOPICAL SCIENCE. 19 



gether of the dust collected was 5 • 7 grains, and the proportion of those 

 particles composed wholly or in part of iron was 2 • 9 grains, or more 

 than one-half. The iron thus sejiarated consisted chiefly of fused par- 

 ticles of dross or burned iron, like " clinkers " ; many were more or 

 less spherical, like those brought to our notice by Mr. Dancer from 

 the flue of a furnace, but none so smooth ; they were all more or less 

 covei'ed with spikes and excrescences, some having long tails like the 

 old " Prince Rupert's " drops ; there were also many small angular 

 particles like cast iron, having crystalline structure. The other por- 

 tion of the dust consisted largely of cinders, some very bright angular 

 fragments of glass or quartz, a few bits of yellow metal, opaque white 

 and spherical bodies, like those described by Mr. Dancer, grains of 

 sand, a few bits of coal, &c. After the examination of tliis dust, lie 

 could easily understand why it had produced such irritation ; the 

 number of angular, pointed, and spiked pieces of iron, and the scorite 

 or clinkers, being quite sufiicieut to account for the unpleasant effect. 

 He thinks it probable that the magnetic strips of iron are laminaj from 

 the rails and tires of the wheels, and the other iron particles portions 

 of fused metal, either from the coal or from the furnace bars. The 

 large proportion of iron found in the dust is probably owing to the 

 metal being heavier than the ordinary dust, and accumulating in 

 cuttings such as those between the two stations named. If he had to 

 travel much by railway through that district, he should like to wear 

 magnetic railway sjiectacles, and a magnetic respirator in diy weather. 



American Researches on the 3Iicroscopy of the Atmosphere. — Mr. 

 Charles Bailey drew the attention of the Manchester Philosophical 

 Society to the subject a propos of the above paper by Mr. Sidebotham. 

 He stated that Mr. Charles Stodder, of Boston, U.S., had been recently 

 making a series of researches on the microscopic contents of the atmo- 

 sphere of that city. Amongst other investigations he was led to 

 examine a fine black dust from a beam in the polishing shop of the 

 United States' Armoury, at Springfield. He found it to contain a few 

 vegetable fibres, some apparently organic fragments, and some broken 

 crystals ; but the great mass of it was made up of amorphous frag- 

 ments of iron, of the yJ^ mm. and upwards in size, as well as curved 

 and irregular fibres and masses of iron, with sharp jagged edges, from 

 5 to 15 mm. in size ; there were also some very minute perfect spheres, 

 probably iron. In trying the effect of the magnet upon this dust he 

 found it removed it from a sheet of paper as completely as if it had been 

 swept off with a brush, and he concluded that the non-metallic por- 

 tions adhered to the iron particles by the thin layer of oil with which 

 all the particles of dust were coated. To prevent this dust passing 

 into the atmosj)here of cities, Mr. Stodder recommended a plan which 

 had been put in practice many years ago in this country, but aban- 

 doned from the indifference of the workpeople, viz. the fixing of magnets 

 in the immediate neighbourhood of grindstones and polishing wheels. 

 In the same report, Mr. Stodder alludes to the labours of two members 

 of the Manchester Society — Dr. Angus Smith and Mr. J. B. Dancer — 

 in examining the contents of the air, and points out an important 

 matter considerably attecting the results of such investigations, viz. 



