(374.) 
880 
cavate the area required for the construction of the 
tunnel. By a simple but most ingenious contrivance, 
every part of the face of unstable clay was firmly 
supported by boards which leaned upon the frame or 
shield, which, in its turn, pressed against the part of 
the brickwork of the tunnel already completed, Each 
workman could remove one or more of these small 
boards at pleasure, and excavate a short way into 
the yielding mass before him, then advance the boards 
and sustain the slippery face. When the whole face 
had thus undergone piecemeal excavation, the frame 
or shield was moved bodily forwards by powerful 
screws, and the bricklayers brought up the masonry 
behind, which was then beyond the reach of injury. 
The idea of the shield was derived, it is stated, from 
Completion a specimen in the arsenal at Chatham, showing the 
of the tun- 
nel, 
Death of 
Brunel. 
(375.) 
Variety of 
his works. 
(376.) 
operations of a testaceous worm which bores under 
water, and which nature has provided witha protec- 
tive covering. But the analogy is certainly indirect, 
since water could hardly retard the operations of 
such an animal. Repeated irruptions of the Thames 
several times drowned the work, which was as often 
abandoned and renewed, but every difficulty was met 
by fresh resources on the part of the engineer. The 
failure of funds was a far more serious obstacle, and 
government at last came to the aid of an undertak- 
ing of such consummate ingenuity that its comple- 
tion was deemed due to the honour of the nation, 
The tunnel was commenced on the 2d March 1825, 
and finished 25th March 1843. Brunel survived the 
completion of his great work above six years, dying 
on the 12th December 1849, aged 81. 
We have not in this brief sketch glanced at one 
half of his ingenious projects and successful enter- 
prizes. Scarcely any branch of his multiform pro- 
fession but received some improvement at his hand. 
The discovery of the condensation of several gases in 
1823, by Mr Faraday, suggested to Brunel their ap- 
plication as a moving power; and his want of suc- 
cess did not arise from any deficiency on his part of 
skill or forethought. He was one of the first to con- 
struct a roof of extreme lightness, somewhat resem- 
bling those now in use for railway stations. He 
erected a suspension bridge in the Isle of Bourbon 
on an original plan; and he pointed out with cha- 
racteristic shrewdness how much of the stability of 
arches depends upon the cohesion of the parts, so 
that the vault may in some cases be entirely dis- 
pensed with. 
It will be understood that we have selected Sir 
MATHEMATICAL AND PHYSICAL SCIENCE. 
(Diss. VI. 
gradation of originality and resource. But as illus- 
trating a class of contrivances altogether different 
from those of Brunel, though like them tending to 
produce a great influence on the improvement of the 
mechanical arts, I will briefly refer to the Caleu- 
lating Machines of Mr Babbage, which have at dif- 
ferent times excited the interest of the public and of 
scientific men, 
Mr Babbage was a fellow student at Cambridge 
( 
with Sir John Herschel and Dean Peacock, and along The @ifer- 
with them he contributed by his writings and per- 
sonal efforts to introduce into that university the 
improved Continental mathematics. Afew years after 
leaving college he originated the plan of a machine 
for calculating tables by means of successive orders 
of differences, and having received for it in 1822 and 
the following year the support of the Astronomical 
and Royal Societies, and a grant of money from go- 
vernment, he proceeded to its execution. It is be- 
lieved that Mr Babbage was the first who thought 
of employing mechanism for computing tables by 
means of differences ; the machine was subsequently 
termed the difference engine. In the course of his 
proceedings Mr Babbage invented a mechanical no- 
tation (described in the Philosophical Transactions 
for 1826), intended to show the exact mutual rela- 
tions of all the parts of any connected machine, how- 
ever complex, at a given instant of time. He also 
made himself acquainted with the various machines 
used in the arts, with the tools used in constructing 
them, and with the details of the most improved 
workshops. Employing Mr Clements, a skilful me- 
chanist, a portion of the calculating machine, very 
beautifully constructed, was brought into working 
order, and its success so far answered the expecta- 
tions of its projector. But, notwithstanding several 
additional grants from government, the outlay on 
this most expensive kind of work soon exceeded them. 
The part actually constructed is now placed in the 
Museum of King’s College, London; it employs 
numbers of nineteen digits, and effects summations 
by means of three orders of differences, Though 
only constituting a small part of the intended engine, 
it involves the principles of the whole. The inventor 
proposed to connect with it a printing apparatus, so 
that the engine should not only tabulate the num- 
bers, but also print them beyond almost the possi- 
bility of error. 
At this stage (1834) Mr Babbage contrived a ma- 
chine of a far more comprehensive character, which The analy- 
he calls the Analytical Engine, extending the plan ‘2! en- 
Mare Brunel as the representative of a class, the 
so as to develop algebraic quantities, and to tabu." 
eminently mechanical engineers, a class now exten- 
(377.) 
Calculat- 
ing ma- 
chines of 
Mr Bab- 
bage. 
sively multiplied, and amongst whom his son, Mr 
Brunel, occupies an eminent position. 
It cannot be expected in an essay like the present 
that I should enter into the details of the variety of 
mechanical inventions which have now become: so 
numerous, and which have been marked by every 
late the numerical value of complicated functions 
when one or more of the variables which they con- 
tain are made to alter their values. Had this engine 
been constructed, it would necessarily have super- 
seded what had already been done, Government were 
not unnaturally startled by this new proposal, and 
as about the same time Mr Babbage’s relations to 
