Dec. 9, 1869| 
NATURE 
161 
of the projector, might be enlarged to any extent. The 
span of the bridge is evidently not agreed upon, nor is the 
construction of the piers determined; we are assured 
that we may have any span we like, and that there is no 
difficulty about the piers ; in fact, the only thing wanted 
to complete this great national work in ¢/7e years, appears 
to be a subscription of eight millions sterling to the credit 
account of the Channel Bridge Company. 
The vagueness of the scheme is the safeguard of its 
promoters. We cannot even describe the propositions 
without running the risk of being contradicted on every 
point ; it is even intimated that it is premature to discuss 
the scientific questions of the Channel Bridge scheme. 
We have a few facts, however, on which we may safely 
enlarge. It is admitted, that from Dover to Blanc Nez, a 
distance of twenty-one miles, a number of piers are in- 
dispensable. In 1868, the distance was to be crossed by 
ten spans, each over 9,000 feet in the clear, and we have a 
diagram of that monster bridge. In 1869 rumour will 
have it that the number of spans is to be increased from 
ten to thirty, making the reduced span still over 3,000 
feet in the clear. With the first proposition we should 
have had nine piers, with the latter, twenty-nine, washed 
by the waters of the Channel. 
Whatever the ultimate number of piers may be, it is 
evident that some of them must be constructed in water 
exceeding 30 fathoms, or 180 feet in depth (according to 
the Admiralty Chart) ; moreover, these piers are to be 
360 feet above high water, making the total height of the 
structure of some of them over 540 feet from the bottom 
of the Channel. Let us see how one of these pyramids 
is to be constructed midway the Channel. 
The projector discards masonry, for no operations 
180 feet below water level are practicable; and as the 
foundations themselves would have to be carried down 
another indefinite number of feet, the depth and consequent 
pressure would render life, and therefore work, impossible. 
A new construction of piers had to be invented, and 
herein should be found the virtue of the design ; let the 
agents of the Channel Bridge Company tell their story :— 
The project depends in effect on two remarkable innovations in 
the construction and establishment of the piers and metallic beams. 
In addition to the considerable height to which the former rise 
above the water (120 yards), the bases of the piers are sunk to 
the bottom at a depth varying from 28 to 52 yards. Except the 
centre one, all the piers at their foundations measure 130 yards in 
width and 87 yards in length, diminishing upwards, and forming 
at the summit a square of 66 yards on each side. The centre 
pier will be half as large again as the others. All the pieces 
composing the work are of cast-iron, and furnish, without in- 
creasing the weight, a power of resistance superior to all other 
kinds of construction. 
As such ponderous piers could not be erected by the ordinary 
means, M. Boutet proposes to construct on the shore their lower 
parts or bases to a height sufficient to rise ten yards above high 
water, and as soon as the iron skeleton is put together and 
bolted, a number of large sheet-iron buoys are distributed about 
the immense surface of the base. At low water the metallic 
framework thus prepared is made to slide upon the shore to low- 
water mark. ‘The tide, in rising, raises this raft or base of iron 
lightened by the buoys, and floats it. A tug steamer then removes 
it to its place, previously indicated by one of a line of buoys at- 
tached to an iron cable, stretched across the Straits at a depth of 
eighteen yards. By raising one of the buoys attached to the raft 
it is made to descend very slowly, the top being just above the 
level of the sea when the base touches the bottom. Thus are 
avoided all the preliminary works under water, which con- 
stitute the greatest difficulty in the way of a bridge across the 
Channel, 
Certainly, we have here Baron Munchausen over 
again. These cast-iron piers, with a base of 390 ft. by 
260 ft., over 200ft. high, we are informed, are to weigh 
about 2,500 tons. What is the thickness of their metal to 
be? Information is wanting on this point; but an iron 
structure of these dimensions, to bed itself on the bottom 
of the Channel, could not be designed of less than ten 
times the weight named. 
Assuming, for the sake of argument, that the rise of the 
tide would float that structure away by the means above 
described—and our business is to analyse the project as it 
is, not to suggest or attempt to improve on it—may we 
not ask with surprise, where would the centre of gravity 
of this floating structure be? Its centre of gravity would 
be about ninety feet above the level of the water, and 
at least one hundred feet aéove the centre of displace- 
ment. Why do our ships not upset, what insures their 
stability, and why do they right themselves? Mainly, 
because their centre of gravity is in its lowest position, 
below their centre of displacement. Here, however, we 
have a floating structure in which the centre of gravity 
would be enormously aéove the centre of displacement, 
and in its highest position. A slight oscillation, a breath 
of wind would overturn it, and suppose it could be floated 
away from shore, it would topple over—right itself upside 
down ; the “sheet-iron buoys” would be uppermost, and 
the structure below them, forming a gigantic wreck some- 
where in the Channel. 
So much, then, about the piers. It may give the ordinary 
reader an idea of the character of this scheme. Shall we 
say anything about the 9,000 and odd feet clear span ? 
At first sight it appears to be a typographical error ; 
surely 900 and odd feet were meant; but then we meet 
with the fact of the Channel being divided into /ex spans, 
so there is no getting out of it. 
The whole proposition is the offspring of a highly 
imaginative mind. Of all the schemes or suggestions to 
cross the Channel by rail, this is the most incoherent. 
There is nothing i tt—not one point of merit. It is not 
bold, because it lacks the spirit of boldness, viz. Sense. 
Not a trace of an engineer’s mind is to be found in it. 
Our asylums produce innumerable schemes of this kind, 
but they are not permitted to disturb the public mind. 
It is a relief to have done with it. We are glad to say 
there are several projects which do not lack either 
sense or ability on the part of the originators. Some of 
them appear practicable, and one or two highly pro- 
mising of success, and these will form the subject of our 
next communication. 
DANA'S MINERALOGY 
A System of Mineralogy : Descriptive Mineralogy com- 
prising the most Recent Discoveries. By James 
Dwight Dana, Silliman Professor of Geology and 
Mineralogy in Yale College, ete., aided by George 
Jarvis Brush, Professor of Mineralogy and Metal- 
lurgy in the Sheffield Scientific School of Yale Col- 
lege. Fifth edition, 8vo. pp. 827, figures 617. (London: 
Triibner & Co.) 
i 
ORTY years ago mineralogy was a fashionable sub- 
ject in England; wealthy people collected minerals, 
though probably but few of those who did so ever made 
mineralogy a serious study. But mineralogy, under the 
