82 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



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. 

 (374.) The idea of the shield was derived, it is stated, from 

 Completion a specimen in the arsenal at Chatham, showing the 

 nel* a ~ P era ti ns of a testaceous worm which bores under 

 water, and which nature has provided with a 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, 

 Death of and finished 25th March 1843. Brunei survived the 

 Brunei. completion of his great work above six years, dying 



on the 12th December 1849, aged 81. 



(375.) We have not in this brief sketch glanced at one 

 Variety of k a if Q ^jg 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 Brunei 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. 



(376.) It will be understood that we have selected Sir 

 Marc Brunei as the representative of a class, the 

 eminently mechanical engineers, a class now exten- 

 sively multiplied, and amongst whom his son, Mr 

 Brunei, occupies an eminent position. 



(377.) It cannot be expected in an essay like the present 

 Calculat- that I should enter into the details of the variety of 



ing ma- . , . . , . , 



chines of mechanical inventions which have now become so 

 Mr Bab- numerous, and which have been marked by every 



bage. 



gradation of originality and resource. But as illus- 

 trating a class of contrivances altogether different 

 from those of Brunei, though like them tending to 

 produce a great influence on the improvement of the 

 mechanical arts, I will briefly refer to the Calcu- 

 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 (378.) 

 with Sir John Herschel and Dean Peacock, and along The di ff* 

 with them he contributed by his writings and per- 

 sonal efforts to introduce into that university the 

 improved Continental mathematics. A few 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- (379 j 

 chine of a far more comprehensive character, which The anal 

 he calls the Analytical Engine, extending the plan f al en ' 

 so as to develop algebraic quantities, and to tabu- gim 

 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 



