Imatges de pÓgina

purposed to make regarding the means best calculated to secure the continuance of the attachment of our native troops to their officers and to the service. This is however of less consequence, as the lesson is already conveyed through the facts which we have stated. It is by treating the Sepoys with kindness and consideration, by stimulating their pride, and by attending, in the most minute manner, to their feelings and prejudices, that we can command, as has been well observed, their lives through the medium of their affections :' and so long as we can, by these means, preserve the fidelity and attachment of that proportion of the population of our immenge possessions in the East, which we arm to defend the remainder, our empire may be considered as secure.

Art. VII.-- An Essay on the Principles and Construction of Mi

litary Bridges, and the Passage of Rivers in Military Operations. By Colonel Sir Howard Douglas, Bt. F.R.S. Inspector

General of the Royal Military College. 8vo. London. ΤΟ ensure a lasting peace it is well that the nation should be

prepared for a war—a preparation best made by scientific and timely investigations of the principles and character of those grand military movements which have, within the course of the last

quarter of a century, so often agitated nations and subverted thrones. The common soldier, in time of need, is soon trained to his art. He needs but bring courage and strength, the beart and the hand, in which Britons are seldom deficient. But the military art itself depends upon abstruse principles of science, which, though mechanically acted upon with success by many who are not even sensible of their existence, can only be perfectly understood by those who have traced them to their source. It is the duty of every man whose habits and talents may have rendered these researches familiar to him, to place the result within the reach and at the disposal of his country, that in the day of need she may avail herself of them; in fact, great service is rendered to the world in general whenever the use of military art can be brought to supersede that of brute force and violence, since it leads to the decision of campaigns rather by the superiority of intellect than by the amount of human slaughter. A skilful and gallant officer has here given us the result of his experience in accomplishing the passage of rivers, a manoeuvre which is frequently decisive of the campaign; and to make good the proposition with which we started, we have only to contrast his ingenious and scientific application of pontoons, rafts, boats, piles, or tressels, with the summary proceeding of a barbarian general encountering a similar obstacle. Mahomet, at the storm of Constantinople,



found a substitute in the bodies of his leading division for all the scientific expedients of the engineering art. His ideas on the principle and construction of military bridges are well explained by Joanna Baillie; they are somewhat rude and savage, it must be confessed, but they proved effectual; and, as Gibbon says, ' the death of the devoted vanguard was more serviceable than the life.'

Some thousand carcasses, living and dead,
Of those who first shall glut the enemy's rage,
Push'd in, pell-mell, by those who press behind,
Will rear for us a bridge to mount the breach,

Where ablest engineers had work'd in vain.' A work useful in itself comes with peculiar grace before the the subject and the duties of the author; and from an officer of Sir public when there is an especial propriety and connection between Howard Douglas's rank and character, selected as he is to superintend the Royal Military College, we receive, with peculiar satisfaction, a practical manual, founded upon scientific principles, for facilitating some of the most important operations of war.

An invaded country may be protected either by a line of artificial fortifications, or by the natural barriers of mountains and rivers. It is against the last obstacles that invaders are usually obliged to contend; and the generals whose names stand highest in military annals have gained their fame as frequently by surmounting the natural difficulties opposed to their progress by rivers, and the defensive lines which they cover, as by victory in the open field. In these cases the necessity of forcing a passage, or establishing communications by military bridges, is so obvious, that the first hostile invader upon record, whom we take to have been no less a person than Milton's Satan, immediately proceeded to secure the advantages which he had gained, by establishing a military bridge extending from the gates of his own fiery dominions, through Chaos, to our own terrestrial globe. Sin and Death formed on this occasion the corps of pontooners, and their formidable operations are thus recorded.

Deep to the roots of hell the gathered beach
They fastened, and the mole immense brought on,
Over the foaming deep, high-arched, a bridge
Of length prodigious, joining to the wall

Immoveable of this now fenceless world.' The importance of Sir Howard Douglas's subject, in a military point of view, did not, indeed, require to be enhanced by quoting the example of the author of war and tighting' amongst us; but the case appears so strictly in point that we could not suppress it, especially as it seems to have escaped the gallant author's extensive researches.


To treat more gravely what is certainly of grave importance, we may remark, that until the Chevalier Du Buat published his treatises on Les Principes d'Hydraulique, the theory of running water (without an accurate knowledge of which the success of the engineer must be a mere matter of chance) was very ill understood. And the erroneous principles previously adopted by Gulielmini and others being still unfortunately enforced in several popular works, are likely to mislead such military men as have not made this branch of natural philosophy their particular study. These errors are happily exposed, and the principles of Du Buat applied and explained in the work before us. Sir Howard Douglas has traced with great accuracy, from the joint operations of sinuosities in the course of a river, combined with the hydraulic impulse of the stream, the effects of running water in forming depositions, and in altering or modifying the bed in which it flows, as well as upon any obstacle opposed to the progress of the current.

The following note coutains a perspicuous and accurate statement of Du Buat's fundamental theorem, with a commentary by Sir Howard Douglas.

M. Du Buat (vol. i. p. 63) gives the following expression for the velocity of running water. V=_ 297 (vr-0·1)

-0.3 (Vr-01) b— hyp. log. Vb+

1.6 Where V denotes the velocity of the water in inches, per second oftime. r= the mean radius, which is the area of the transverse section of the

stream divided by its perimeter, both taken in inches. b = the distance in which the fall or descent of the running water is

thus if the fall of a river is one foot per mile, or 1 inch in the distance of 5280 inches, then 7 is the fall, and b = 5280 inches. If & = the velocity acquired by the perpendicular descent of a heavy body at the end of the first second of time, then, the motion of the water being supposed uniform, g x 7or will denote the accelerating force, relative to the slope -ý (that force being as the velocity); V2


ving and putting - for the resistance, we have -= whence V=

b where m is some function of vr to be determined. This is Du Buat's fundamental theorem.

From many experiments with water running through different pipes, he finds the mean value of m to be 243 • 7 (Vr-0:1) nearly, or m= 243 •7 r nearly, by neglecting 0 1: now g=386 inches English measure, whence mg = 386 x 243 • 7 r, and the equation V=vme 306 · ✓r

✓6 becomes V= ✓b

1 b


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computed with V mg

27 · 62


Du Buat has considered the effects of tenacity, friction, &c. in obtaining his final expression; but it may be remarked, that the velocities

V mg =V, are all nearer those found by experiment in

✓b the River de Hayne, than those resulting from the other equation. Thus, in the following table, the velocities found by experiment are in the first column; those computed from V= 297 (r-0.1) 0:3 (Vr


3 ✓b-hyp. log.b+ 1.6

28 0:1) are in the second column; and 35 · 11

297 vr

31.77 28 · 76 the velocities given by V=

29.8 ✓b 13.61

10.08 12 · 07 in the third: (sce p. 63, vol. i.) If we


15.96 10 · 53 12.7 adopt the expression


✓b then any two of the quantities V, r, b, will readily give the third; thus

V? b putting a = 306 · 7; then r = when V and b are given; and

a a? b when V and r are given.'--pp. 15–17.

V2 In this note Sir Howard Douglas has proved the important fact, that in some cases the velocities computed from the expression 297 VT

are nearer those found by experiment than those resulting ✓b from the final expression V=

297 (Vr_0:1)


vb hyp. log. 7b+1.6 But it ought to be noticed that a general rejection of the corrections for tenacity and friction, merely because the velocities computed from the pure expression agree more nearly with those found by experiment in one particular river, may lead to inaccuracy. It would have been more satisfactory to explain the nature of the corrections, and to compare the results yielded by the whole expression with those found by actual experiment in various rivers, leaving the practical engineer to decide every case upon its own peculiar circunstances. That this is the more accurate view of the subject must be obvious, when it is considered that the corrections must vecessarily vary according to the character of particular rivers. The correction for tenacity, for example, occasions a more sensible diminution of r, the mean radius, (the area of the transverse section divided by its perimeter,) in small than in large rivers. And we may also notice that the correction as given in Du Buat's fifth chapter, for v b the square root of the slope, ought to have been illustrated and explained. An extension of this useful and, so far as theory goes, fundamental department of the work would also be desirable, and ought to exhibit a collation of the doctrines of the last edition of Du Buat's work, with Prony's · Théorie des Eaux Courantes.'

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In general, however, this correct and clear statement of an important theorem is likely to be of practical advantage to the civil as well as the military engineer; and Sir Howard Douglas remarks that in exploring rivers in unknown countries it will also aid the traveller to ascertain the declivity of the stream, and the elevation of the country through which it flows, by merely measuring the velocity and width, and taking its several depths. These observations repeated from time to time, and carefully noted, may afford a mode of levelling which will supply the occasional want of experiments by the barometer.

The discussion of these principles in hydraulics occupies the first section in the work before us. Having laid down general rules for ascertaining the nature and force of the element to be surmounted, Sir Howard Douglas gives in separate sections an account of the various expedients which war’s vast art' affords for surmounting them. Pontoons of course occupy the first section, and accurate tables are given calculating the weight borne for every inch of immersion, and thus at once ensuring to the engineer the information necessary for his profession. Directions for constructing the pontoons, and for laying them where they are to be used, are also given, with many valuable practical hints against the means of destruction to which the enemy may have recourse.

The next section respects bridges of boats, and contains a description of that which was constructed by the Duke of Wellington for repairing the bridge at Alcantara, and that for passing the Adour in 1814; of both which operations excellent plans are given. An account of the splendid movement by which the left wing of the British army, under the present Lord Hopetoun, crossed that river, is, to us at least, one of the most interesting of the historical illustrations by which Sir Howard has judiciously enlivened his work, and we willingly select it as an example of his style of narrative. It had been designed to make a lodgement on the opposite bank by men transported over, during the night, upon rafts formed of pontoons : but morning broke before a raft could be formed, and thus this memorable movement was destined to take place in open day-light.

"A few men were first pushed over in the row-boats attached to the pontoon train, and drove away the enemy's piquets;-rafts of pontoons were immediately constructed, but not being found to answer, owing to the great strength of the current, boats and pontoons used as row-boats, when the tide was slack, were employed to reinforce, as fast as possible, the small force sent over in the first instance. During all this time demonstrations of an intention to pass the river opposite to the enemy's

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