AIR OF NEW YORK SUBWAY—SOPER. 663 
The dust had a marked capacity for soiling linen and other articles 
of clothing. Straw hats and the light-colored garments worn by pas- 
sengers of both sexes in summer were likely to be soiled by coming in 
contact with even small accumulations of the dust. 
When examined microscopically, the dust was found to be com- 
posed of particles of many substances, conspicuous among which were 
fine, flat plates of iron. In fact, these iron particles could often be 
seen with the naked eye, glistening upon the hats and garments of 
persons who had been riding in the subway. 
Particles 2 mm. long were on one occasion taken from a magnet 
which had been carried in the hand on a ride of twenty minutes in 
the cars. By comparison it was found that magnets hung up in the 
Fic. 9.—MAGNETIC FIELD FORMED BY SUBWAY DUST. 
subway collected more particles of iron than magnets of the same size 
and strength hung up in an iron foundry or a dry grinding and pol- 
ishing establishment. Fig. 9 shows a magnetic field formed by sub- 
way dust. 
The size, as well as the number, of the particles depended upon the 
place where they were sought. 
Many were so small that they floated in the air as dust. These 
generally escaped notice, except where beams of sunlight entered the 
subway or where the subway air emerged from some small opening 
into the sunlight in the streets, under which circumstances they glis- 
tened plainly. 
41780—08-——46 
