SiGERSON — On the Atyno^pliere. 
23 
the air than by making a carefnl examination of particular atmo- 
spheres, as well as of the general air. A commencement was made in 
my former paper, when I made the broad divisions of city air," 
country air," and the sea breeze" — and added to them the more 
limitedly special air of our dwellings. The examination of special at- 
mospheres has since engaged my attention. 
My mode of operation, here, has been to collect the sediment of the 
atmospheres, from ledges where it was deposited on a level with or above 
the height of man. In this way, making also an inspection of the air, 
I was certain to obtain matter identical with that which he had taken 
into his lungs. When this was done, I examined the collections with 
care in the microscope, applying suitable tests, and employing various 
object-glasses from the one-inch to the one-eighth inch. Some par- 
ticles I measured with the micrometer. Then, when magnified gene- 
rally with the one-eighth objective, I drew them on paper to the same 
apparent size ; these portraits I next vastly enlarged for the diagrams 
which I have placed before the Academy. 
Iron Factory Air (Plate VIII.). — The deposit was taken off rafters, 
about twelve feet high above the clay floor. It was black and friable. 
Microscopically examined, it was found to consist of carbon, ash, and 
iron balls, of the relative sizes shown. The carbon formed the largest 
masses, next came the ash, and finally the iron ; the extremely minute 
dust of this dust was, however, the powder of carbon and a little ash. 
The carbon, large and little, was to be identified by its hue, and in some 
cases by its fibrous character ; the ash was reddish, or white, and 
opaque. Some of the finest powder of the dust might be of from 
ToU.o 0 0^-'^ to 5 0 olo 0 0^^ in diameter. 
Besides the substances already mentioned, there were transparent 
particles having a glossy fracture, and presenting the appearance of 
glass. I believe them to be actually particles of glass, formed in the 
furnace by fusion of sand flung in to assist in the operation of welding. 
On making a minute examination of the iron balls, or, more 
strictly speaking, of the balls of ferroso-ferric, or magnetic oxide of 
iron, I discovered that they are, in fact, hollow spheres — iron bal- 
loons — which break readily on being pressed between two glasses. 
Then I found, on looking at one of the fragments, that the iron here 
present, was translucid You could see the light through it ; and in 
it I detected a granular structure. I believe the translucency of fer- 
roso-ferric oxide has never before been recorded. On making a mea- 
surement of these iron bombs, they were found to vary from 3- ^^th 
of an inch to j^\yoth. The general size was from goVo^-'^ 
Comparing the diameter of the bomb with the thickness of its shell, I 
came to the conclusion that in some, at least, the thickness of the shell 
was jgth of the whole diameter. In a bomb -^-^q-q^ of an inch in 
diameter, the thickness of the shell might be taken as ^-o.uoU^^ 
inch. This calculation I made in order to try to find at what thick- 
ness iron becomes translucid. 
There were no spores or seeds present — no fibres of any kind, the 
result of spores developing — no fibres except of carbon, some contorted 
