9 8 
science:. 
A chapter on the history of the germinal layers is 
promised in volume second. It is pleasant to find from 
the names of Agassiz, and Brooks, and others, that 
Embryology is gaining a sure foothold in this country. 
The book throughout evinces the greatest ability and 
care. Clearness and truth will make it attractive to the 
student, and it may safely be predicted that a fresh 
impetus in embryological research among young students 
in this country and abroad will date from this publica- 
tion. If this prove to be the case, the author may well 
feel repaid for his labor. H. F. O. 
On Angular Aperture of Objectives for Micro- 
scopes. By Geo. E. Blackham, M.D., F.R.M.S. New 
York Industrial Publication Company. New York, 
1880. 
We are glad to see that the vexed question of the an- 
gular aperture of the objectives has at length been treated 
in an exhaustive manner by Professor Blackham, who, 
by an untechnical method of treating the subject, has 
endeavored to interest a wide range of readers. The 
work has been produced in handsome form, and has 
eighteen sheets of diagrams. A critical review of this 
book will appear at a later date. 
COAL. 
BY P. W. SHEAFER, m. e., pottsville, pa. 
II. 
The fearful loss of good material involved in 
mining and preparing Anthracite, as shown in the ac- 
companying tables, though greatly to be deplored, 
seems to be almost inevitable. The disposition of the 
coal in large solid beds, and in highly inclined posi- 
tions, involves strong supports to keep the superin- 
cumbent mass from crushing and closing the avenues 
to the mines ; and these supports must consist of 
massive pillars of the solid coal itself. Wooden props, 
however ponderous and strong, can only be used for 
the minor supports. Some of this pillar coal is ulti- 
mately removed, but much of it is inevitably lost, 
especially in the larger beds which frequently range 
from 20 to 40 feet in thickness, and are often inclined 
at an angle of from 40 to 70 degrees. 
It is estimated that not more than 66 per cent, of 
the coal is ever taken out from the mines. That 
which is brought to the surface is run through a huge 
structure from 80 to 100 feet high, very appropriately 
called a “ breaker,” ingeniously contrived for the de- 
struction of coal. There are over 300 of these im- 
mense buildings in the Anthracite region, costing on 
an average $50,000 each, or an aggregate of $15,000,- 
000. To the top of these the coal is hoisted, and 
then descends through a succession of rolls and 
screens, emerging at the bottom, in a series of assorted 
sizes, from huge blocks of lump coal to unmerchant- 
able dust, which forms a grievously large proportion of 
the whole. This process involves a loss of good coal, 
equal to 20 or 25 per cent, of the entire quantity 
mined. For the coal wasted in mining, say 40 per 
cent., and in preparing, 25 per cent., no one is paid ; 
it is a total loss to landowner, miner and shipper. 
Plans for utilizing the waste coal dirt, or culm of 
Anthracite collieries, have been frequently suggested, 
but none have come into general use. The Anthra- 
cite Fuel Company, at Port Ewen, on the Hudson, in 
1877, used 90 per cent, coal dust and 10 per cent, fuel 
pitch, and made 300 tons of fuel per day, consuming 
over 50,000 tons of culm. The Delaware and Hud- 
son Company also use at their mines 60,000 tons per 
annum. They now ship all their coal down .to pea 
sizes, and consume the culm in generating stfeam. If 
all our coal companies would follow this excellent 
example it would enable them to sell half a million 
tons more coal, and burn the same amount of refuse, 
thus earning or saving half a million dollars per 
annum, to add to their revenues. The Philadelphia 
and Reading Railroad Company has recently intro- 
duced a method of burning coal dust in the furnaces 
of its engines, and the plan appears to meet with suc- 
cess. 
The amount of water which drains into a mine from 
a mile or more of surface is enormous, for the average 
amount of rain and snow fall is 58,840 cubic inches 
per square yard annually, and the mines are liable to 
absorb not only the rain fall on the surface immedi- 
ately over them, but all that which by contour of 
the surface, or by converging strata, tends towards 
them. On an average possibly five tons of water are 
hoisted for every ton of coal raised — another loss 
chargeable to mining. 
The preponderance of waste coal seems excessive ; 
but the writer’s experience in surveys of certain tracts 
of land, and in preparing maps which show the area 
exhausted, compared with the amount marketed from 
ten or more colleries, in a period of 20 years, proves 
that the loss is not over-estimated, especially in the 
Mammoth Bed, whose average thickness is 25 feet. 
An eight-foot bed of coal yields much better in pro- 
portion. When they exceed six or eight feet in thick- 
ness, especially if steeply inclined, they are not only 
expensive to mine, but a large proportion of the coal 
must be left to support the rocky roof. 
The Bituminous coals, particularly those of the 
United States, are not subject to these serious losses, 
and are quite cheaply mined and prepared. No 
"breakers are required, as the only division is into 
coarse and fine coal, which are easily separated by 
screens ; and the fine coal can be readily converted 
into coke, making a better condensed fuel than the 
coal in its natural shape. The Bituminous beds are 
nearly horizontal and rarely more than six feet thick, 
so that it is not necessary to leave extensive pillars ; 
and as the coal is above water level, or in shallow 
basins, it is not necessary to put up extensive hoisting 
and pumping machinery. The simple, natural venti- 
lation of American Bituminous mines also does away 
with the extensive and costly appliances for this pur- 
pose of Anthracite mines, in spite of which so many 
miners annually fall victims to the noxious gases. 
The total amount of coal still to be mined, accord- 
ing to the accompanying tables, is 26,361,076,000 
tons. The total waste, as experience has shown, is 
equal to two-thirds of the coal deposit, and reaches the 
appalling amount of 17,574,050,666 tons, leaving us 
only 8,787,075,533 tons to send to market. In all our 
calculations of Anthracite we have counted the area 
as if in a level plain, and made no allowance for the 
undulations which must necessarily increase the 
amount of coal. But as many of the flexures are 
abrupt and broken, making much faulty and refuse 
coal, it will cover any over-estimate of area or thick- 
ness we have made in our calculations. 
Our tables show that 360,017,817 tons have been 
