' 
. 
—— ae 
a 
Fob. 27, 1873) 
. 
that other substances besides ozone affect Schénbein’s 
papers, which are not “ browned” by the way. 
We are glad to see that the organic impurities intro- 
duced into the air by the respiration of animals receive 
due attention, and that the gradual deterioration of 
health caused by breathing impure air is well insisted on. 
The pages on the ventilation of sewers, &c., want re- 
writing, and the three conclusions all require alteration ; 
they are as follows :— 
1. “That no sewers, or drains, or pipes, should run into 
drains in dwelling houses,” This sentence as it stands is 
too ambiguous to be of any value, 
2. “If this be impracticable, all sink pipes or waste 
pipes should be broken off at least one foot above the 
trapped grating into which they discharge.” The first 
clause here is unnecessary and even misleading ; it would 
be well left out. 
3. “On no account should a cesspool be placed within 
the wails of a dwelling, but as far as possible from the 
house.” Surely it would have been weil here to advise 
the abolition of these nuisances where not absolutely 
impracticable, or at any rate their construction of suitable 
impervious materials. 
This is certainly the weakest part of the book, and shows 
how little such matters are generally understood even yet. 
On the other hand the remarks on the relations of 
filth and disease are excellent: “the negligence of the 
upper and lower classes of society alike, in these matters, 
entails terrible calamities on both, The fevers and con. 
tagious disorders arising from the neglect of the poor, 
either on their own or on our part, find their way into the 
dwellings of all classes, and equally establish disease. 
The poorer class cannot with impunity live in a state of 
unnecessary filth and dirt; neither, on the other hand, 
may the rich without danger neglect the sanitary and 
physical conditions of the poor around them.” 
The currents of air produced in rooms by differences 
in the temperature of various parts should, if classed with 
winds (the aspirating effect of which latter is not men- 
tioned), be at any rate in a separate subsection ; and the 
law of diffusion of gases does not hold for vapours, and it 
is certainly not in virtue of it that “the dispersion of 
vaporous matter” in the air is effected. Otherwise the 
pages on ventilation are well worth study, and the same 
may be said of the part devoted to disinfectants, which 
contains much sound practical information. 
The second part of the book, on “the impurities of 
water and their removal,” is decidedly good ; some of the 
best known cases illustrating the connection between 
polluted water and specimens of cholera and enteric fever 
are given, and the dangers to be apprehended from the 
habitual imbibition of impure water (apart from specific 
diseases) are insisted on ; the presence of more than a 
small amount of chlorides is rightly pointed out as a 
suspicious circumstance, and the simpler tests for the 
detection of the various impurities are concisely de- 
scribed ; then follows a short account of the methods to 
be employed for the purification of presumably impure 
water by means of boiling, filtration, &c., and several of 
the best household filters are mentioned. Clark’s process 
is, however, only casually alluded to, and not by name. 
We are glad to find that the importance of a continuous 
water supply especially to the poorer classes is pointed out. 
NATURE 
319 
The book before us will, with a small amount of correc- 
tion, do valuable service if widely circulated, as we have 
little doubt that it will be. If we have drawn attention to 
a few defects in it, we have done so because we believe 
that it is of the utmost importance that popular manuals 
should contain exact information, and enter as little as 
possible into disputed points. W.. Bice 
OUR BOOK SHELF 
The Coat-fields of Great Britain, &c. By Edward Hull, 
M.A, F.R.S., &c. Third edition. (London : Stanford.) 
THIS new edition of Prof. Hull’s well-known work is in 
most respects a great improvement upon the previous 
ones. Not only are the coal-fields of Britain itself treated 
of in more detail, but those of the colonies and foreign 
countries also come in for fuller notice. The introduc- 
tion of numerous excellent maps illustrative of the English 
coal fields imparts an additional value to the volume, by 
enabling the reader to grasp at a glance the leading fea- 
tures in the geological structure of the districts embraced, 
Prof. Hull has, moreover, 1 rgely availed himself of the 
report prepared by the recent Coal Commission, the chief 
results of which have been embodied in his work. That 
report, as everyone knows, has calmed the fears of those 
who saw looming in the near future the exhaustion of 
our coal supplies and the consequent decline of our 
industries, It is comfortable to reflect upon the 
fact that we have still 146,480 millions of tons avail- 
able within a depth of 4,000 feet, and something like 
48,465 millions of tons at a greater depth. From the first 
of these estimates, Prof. Hull would deduct one-twentieth 
for coal-seams under two feet in_ thickness, thus leaving 
the available quantity of 139,156 millions of tons lying 
within a depth of 4,000 feet from the surface. Beyond 
this depth he believes it will not be practicable to pene- 
trate, owing to the effect of increasing temperature and 
pressure. This, however, is quite an open question. No 
good reason can be shown why ventilation should not be 
made effective at a still greater depth than 4,000 feet. If 
the deeper-lying coal should ever be needed no doubt the 
engineers of the future will be equal to the occasion and 
able to render it available. Then, as regards the effect of 
pressure, we know from actual experience that the “ density 
of coal-seams is not perceptibly greater at 500 or 600 
yards than at half that depth.” One might almost have 
inferred as much. beforehand, for many of our coal-fields 
which are now being worked at easy depths must at one 
time have been covered with thousands of feet of strata, 
long since removed by denudation; yet the seams 
in such fields are not denser than those of fields which do 
not appear to have been covered by such great rock 
masses. Again, we have heard mining engineers assert 
that the increased pressure in the deeper pits actually aids 
in the excavation of the coal, which comes away in larger 
lumps than would be the case with a similar coal in shal- 
lower workings. But whether or not it will ever be neces- 
sary to sink deeper than 4,000 feet, there can be no doubt 
that there is yet abundance of fuel above that limit to 
keep our furnaces going for many long years to come, 
and if Britain be destined ere long to retire from her 
place in the vanguard of nations her loss of prestige will 
probably be due to other causes than the exhaustion of 
her mineral resources. 
The author expresses himself strongly on the subject of 
“waste” in working the coal, but not a whit more strongly 
than is necessary. Everyone who has any acquaintance 
with British collieries knows how lamentably great this 
waste is, amounting in some cases to so much as 4o per 
cent. No doubt, in miny of our best conducted collieries 
waste is reduced to a minimum, but there is still woful 
