1872.] Notices of Books. 361 
Apart from the valuable theory which Mr. Jordan has advanced 
in his work, we think he has performed a duty in thus clearly 
proving the errors of a theory too assiduously expounded. But 
it must be said that we lay down Mr. Jordan’s pamphlet with 
feelings of the most intense surprise—surprise that such a 
theory should meet with the slightest favour, and that Dr. 
Carpenter should have evolved it in any moment but those of 
“unconscious cerebration.”’ 
Coal Economy. By Frep. Cuas. Danvers, Assoc. Inst. C.E., 
of the Public Works Department, India Office, &c. London: 
W. H. Allen and Co. 1872. 
WHuILE public attention has of late years been directed again 
and again to the serious waste of coal consequent upon our 
present systems of coal mining, and to the recklessness with 
which the fuel is too often consumed, it is curious that little or 
nothing has been written on the injury and waste which the 
coal suffers after it emerges from the pit’s mouth, and during 
the successive stages through which it passes before reaching 
its final destination. 
Yet this loss is by no means insignificant; for it is obvious 
that the coal in the course of being screened, and during 
its transport, whether by land or water, must be continually 
subjected to movements which tend to cause disintegration, 
and inevitably result in the formation of more or less small and 
comparatively useless coal. It is pleasing to find that this 
neglected phase of coal economy has received the careful 
attention of Mr. F. C. Danvers, who in the work before us dis- 
cusses the several sources of waste, and points out the best 
means of utilising the small coal, whilst incidentally he offers 
much useful information on the machinery employed in connection 
with the mineral traffic. 
It is not with the waste in underground working that our 
author has to deal. That question was fully examined by the 
Coal Commission, and Mr. Danvers’s work begins exactly 
where that of the Commissioners ended. Suffice it, then, to 
say that in the steam collieries at least 40 per cent is usually 
lost in working by the “pillar and stall” system, and about 15 
per cent by the “long wall” system. If the small coal be raised 
to the surface with the large coal, the pit is said to be worked 
on the “‘ altogether” principle ; if the small coal is left under- 
ground it is worked on the “separation” principle. In the 
former case as much as one-half of the output may consist of 
‘small,’ whilst in the latter case only from 5 to Io per cent 
passes through the screens. The author describes the con- 
struction of several forms of screen used in the South Wales 
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