This is a very convenient form for a rain gauge; but those which have been sent to the Royal Engineer stations are merely zinc boxes, 10 inches each way, with graduated glasses, as in fig. 6. The moveable partition (P) in the receiver, is to prevent loss

from evaporation; the quantity received is poured into the glass measure, which, as it only measures a quarter of an inch if full, may have to be filled several times.

Indications of Change of Weather.

The words* Fair, Change, Rain, &c. &c., which are usually engraved upon common barometers at 29, 29 5, and 30 inches, &c. &c., on the scale, are so far correct, that if the mercury is rising or falling steadily to those points, such weather may confidently be expected, particularly if the hygrometer also indicates a decrease or increase of moisture in the air; but a sudden fall of an inch in the barometer would almost certainly be followed by a storm, though the mercury might still be far from the level at which the word "Stormy" is usually written. So, again, we may have a continuance of fine weather, though the barometer never reaches the point for "Set Fair” weather. A gradual rise or fall indicates a change of weather which is likely to be of some duration; whilst a sudden change in the barometer indicates a corresponding change in the weather. When the fall of the barometer is sudden, it indicates a vacuity over the spot, into which the air will rush to fill it, and this rush of the air will be in proportion to the fall of the barometer; in great storms and hurricanes it has ranged upwards of three inches, that is, from 28 to upwards of 31 inches in height this great height, when the storm is passing away, is due to the accumulation of air over the spot, after closing in from opposite sides. A falling barometer, when the dew point is high, indicates rain; but if the dew point is low, it indicates wind without rain. The hygrometer should always be observed in conjunction with the barometer; its indications are very important aids in prognosticating a change of weather, and the nature of the change.

* At great altitudes these words have no meaning whatever, they would be above the extreme range of the mercury.

In the Attack and Defence of Fortresses,' in this work, the subject of Military Mines was very briefly alluded to. This branch of Fortification is, however, to the Military Engineer, of paramount importance.

By a study of the 'Attack of Fortresses' it will have been seen how irresistible is its march; that the means of destruction at the disposal of the besieger, and the mode of application, render the reduction of a fortress a matter of calculation. The advantages of position, number, and material, are all on the side of the besieger. But so soon as the latter is compelled to engage in subterranean warfare, these advantages cease, or rather are transferred to the besieged. It is a very remarkable change. The French authors, Gumpertz and Lebrun, speaking of the difficulties which a besieger would experience should he attempt to carry on his approaches on a glacis defended by countermines, without in the first instance destroying them, say— "The loss of a great number of men, and the discouragement of the whole besieging force, perhaps even their defection, would inevitably follow such a resolution. When, therefore, the front of attack is countermined, the besieger must call the miners of his army to his aid. This corps,-stimulated by the importance of the services they are called upon to perform,-proud that the progress of the attack is committed to their charge,-convinced that, although their operations are concealed from the eyes of their comrades, yet their daring deeds are not the less appreciated by them,-actuated by all these motives, penetrate below the surface of the earth, armed with thunder, to seek their enemy, to struggle with him in darkness, and finally to triumph over him ;--their victory being incontestably the fruit of true courage,-of skill united to valour." And further

“The miners of the besieged have, also, an equal claim to glory: although finally compelled to yield the victory to their opponents, it is an animating spectacle for the besieged to witness, that, by their art, the hitherto imperious march of the attack is for a time averted: so soon as it is known to the besieger that the ground over which his attack must pass is mined, his operations become, as it were, paralysed. The mine produces an effect in the ranks of the besieger far greater than the fire from the ramparts. The imagination exaggerates the danger, ever appearing more formidable as it is mysterious and obscure. It is in vain that the bravest of the besiegers attempt to push on the attack and overcome at all price the obstacle which impedes their advance. Yet a handful of men, by a slow, dangerous, and most difficult process, conquer, where numbers and courage succumb,-a striking example of the superiority of industry and skill over force. And now a struggle is commenced and carried on amidst silence and darkness. The besieged, who cannot avail himself of such large charges as are fired by the besieger, still retains on his side all the advantages of that science which foresees, observes, calculates, and regulates everything. His attentive ear is directed to all the points by which the besieger can advance. If the latter is heard, he is lost a volcano whose existence he suspected, but whose destructive effects he could not escape, shatters his galleries, and buries him amidst its ruins; and yet no outward sign betrays to his companions the misfortune which has befallen him. The besieger then is satisfied if he can manifest himself by any effort whatever, and amassing hurriedly a quantity of powder, explodes it in the hope of narrowing the circle of operation of the mine of the besieged, while he

By the late Lieut.-Col. J. Williams, R.E.

establishes a lodgement on the edge of the crater he has produced. But the besieged does not leave this newly acquired position long undisturbed, and by a mine which can be fired with sure and certain effect, overthrows his gabions and destroys the lodgement. Such is the débût of a subterranean warfare: its continuation and its close are but a repetition of the same process. On the side of the besieger there are precaution and perseverance; on that of the besieged, care and activity; in both, patience and courage. The last scene in the combat shows the besieged repulsed but not conquered; while he may fairly proclaim that, for the continuation of the struggle, it is not courage that is wanted, but arms.'

There can be no doubt that all Engineers, who wish to restore the balance between the attack and defence, should direct their attention to subterranean defensive operations; for a successful application of these may cause either the raising of a siege or a very considerable prolongation of its duration, and the time thus gained is often invaluable.

Military mining as a system has, however, hitherto played a secondary part in the operations of war. The only records of its extensive employment are to be found in the accounts of the siege of Candia by the Turks, in 1669, Schweidnitz, in 1759, by Frederick the Great, of Silistria in 1854, and Sebastopol in 1855. Notwithstanding, however, this disuse of mines in actual warfare, the subject has received considerable attention at different periods from distinguished Engineers; and systems (as they are termed) of countermines are consequently very numerous. Among the most celebrated of these systems are those of Goulon, Vallière, Mesgrigny, Delorme, Cormontaigne, Rugi, Mouzé, Dubuat, and Marescot. The object of the Engineer, in each system, appears to have been so to dispose his subterranean works as to destroy the various surface approaches of the besieger when in advance of his third parallel; but more particularly the breaching batteries which he established on the crest of the glacis. A brief notice of the various circumstances under which, at different periods, mines have been employed in war, will properly preface the present article. Their earliest application appears to have been made in the Attack, and simply for the purpose of gaining access into the interior of fortified towns by means of a subterranean gallery passing under the walls of the fortress. The obvious inconveniences attending such a mode of attack soon occasioned its disuse, but a more successful employment of mining followed; viz. continuing the galleries only as far as the foundation of the principal wall, and then excavating the ground for a certain breadth (say about 100 feet) under its base, the masonry being temporarily supported by wooden props, which were set fire to when the arrangements were ready for the assault, - -so that the wall, being left without support, necessarily fell, and opened a breach to the besieger.

The introduction of mines in the Defence naturally followed their employment in the Attack. The earliest subterranean defensive position consisted of a gallery placed in advance of the foot of the wall, and termed an envelope gallery. From this gallery the garrison pushed forward small branches or galleries for the purpose of being warned of the approach of the enemy, and by these means to prepare themselves to resist his attack. The defenders occasionally employed these subterranean defences for overthrowing the towers, battering-rams, and other offensive weapons of the besieger. It may be remarked here, that from the circumstance of mines having been introduced in the Defence for the purpose of counteracting those employed in the Attack, the term countermine was given to defensive mines by the Engineers of that time; and the name, although apt to mislead, is still retained: some writers, however, apply the terms 'offensive and defensive mines;' and these latter designations appear the most appropriate.

Such was the nature of subterranean warfare previously to the invention of gun

powder; and, what is remarkable, almost two centuries elapsed between its invention and the use of it in mines. The circumstance under which the first mine charged with powder was exploded is thus narrated by Bousmard.

"The French, under Charles the Eighth, in 1503, having overrun with great rapidity the kingdom of Naples, were as quickly dispossessed of their conquest by the Spaniards, under the famous Gonsalvo di Cordova, surnamed the Great Captain. A single post, defended both by nature and art, alone remained in possession of the French, and resisted for three years the united efforts of the Spanish and Neapolitan armies to reduce it: this was the Castello del' Uovo, in the bay of Napies, constructed on a rock surrounded on all sides by the sea, except where a narrow isthmus formed a connection with the main land; across the isthmus, however, a deep ditch or coupure cut in the rock, prevented all access into the interior. The natural defensive advantages of the position account for the length of the defence. The ingenuity of a Spanish Captain, Pedro Navarro, gave at length the victory to his countrymen. He took advantage of the contour of the rock to open, unseen from the castle, a gallery which he contrived gradually to drive forward till it had arrived under the castle; and then placing a quantity of powder, he ignited it by a process which allowed the miner who applied the quick-match time to escape. The explosion caused a violent commotion of the rock; great masses of it, together with a portion of the walls of the castle and a large proportion of the garrison, were precipitated amidst flame and smoke into the sea. Then the élite of the Spanish and Neapolitan armies landed from boats, and easily carried the breach made by the mine, but weakly defended by a small number of the garrison, already dispirited by the consternation produced by the explosion." Such was the success of the first experiment in mines charged with powder.

It appears that the success which attended this mode of destroying defensive works soon caused its very general employment: at the close of the fifteenth and at the commencement of the sixteenth centuries access into fortresses was very generally made by mines; and indeed so powerful at this time seems to have been their influence in the attack, that it was not unusual for the besieger, after preparing his mine, to invite the besieged to inspect it, with a view of inducing the latter at once to surrender.

To return, however, to the Defence: the galleries which had been employed previously to the invention of gunpowder, were found to possess certain unlooked-for advantages after the introduction of its use in offensive mines. It was observed that when a charge of powder was exploded in their vicinity, its surface effect was very much diminished under such conditions the mine was said to be éventée,-'éventer la mine.' The old galleries also retained their original purpose of informing the besieged of the proximity of the enemy, and enabling him occasionally to break into the gallery, and destroy the works.

The first application of powder in defensive mines consisted of small charges; the explosion of which, without causing any surface effect, ruptured the besieger's gallery, and suffocated its occupiers: this operation was called 'giving the camouflet to the enemy's miners.' From the employment of camouflets to the introduction of more powerful mines was but a step.

By the explosion of larger charges, not only were the surface approaches of the besieger for a certain distance destroyed, but his galleries, which were at a less distance from the powder than the surface of the ground, were likewise blown in: so soon as defensive mines were thus far perfected, the employment of powder in subterranean operations, which at first certainly favored the attack, became a powerful auxiliary to the defence. It is obvious, that when the besieged had, beforehand, arranged a system of galleries under his glacis, he must necessarily possess many advantages over the besieger, who had to construct his subterranean approaches in

ground already occupied by the mines of the besieged. The attack, in place of advancing simply by furrowing the surface of the glacis, was now compelled to engage in under-ground operations, the progress of which must necessarily be slow, and the issue uncertain: superiority of force no longer availed the besieger, while the surface attacks, brought almost as far as the foot of the glacis, became for a time stationary, and exposed to the near fire of the musketry of the fortress.

To increase still more the advantages of defensive mines, various modes of placing them were proposed for destroying the trench cavaliers, overthrowing the breaching batteries of the attack, and blowing the guns into the ditch. Systems of defensive mines, arranged on different levels, were likewise proposed, with the object of destroying the same works of the besieger several times in succession.*

The experiments of Belidor caused, however, these complicated systems to fall into disuse, and deprived defensive mines generally of some of the advantages they had hitherto possessed. To Belidor is due the discovery, that, by the employment of large charges, the galleries of the besieged could be destroyed from a considerable distance. Before his time, it had been generally conceived that no crater, the diameter of which exceeded twice its depth, could be formed by the explosion of a mine, and the interior effect was also supposed to be proportionally limited; but as soon as the fallacy of this opinion had been exposed by Belidor,-who proved that the radius of rupture with large charges much exceeded the limits usually assigned to it, -the attack received considerable advantages. The besieger availed himself of this increased range, and, by means of it, cleared the ground for a considerable distance around him, without pushing his galleries within the much narrower limit of the mines of the besieged. This, however, will be more particularly explained in the 'Attack of a System of Defensive Mines.' J. W.

Note. The subject will be treated under the following parts or divisions: 'Practical Operations of Mining,'-'Charges of Mines,'-'System of Permanent Defensive Mines,' -'Attack and Defence of a System of Defensive Mines.'-Editors.

PART II. -PRACTICAL OPERATIONS OF MINING.t

The essential difference between Civil and Military Mining is, that in the former the works are, for the most part, carried on at greater depths below the surface of the earth, and in solid rock; whereas military mining is what may be termed superficial, and consequently the miner works through the more recent formations of earths and sands, which, from their little tenacity, he has to support as he advances with wooden linings it is in the adjustment and fitting of these linings that the chief art of the military miner consists.

The excavations made by military miners are, when vertical, called Shafts; when horizontal, or when slightly inclined, and exceeding in dimensions 3 feet by 4 feet, Galleries; when under these dimensions, Branches: when galleries or branches are inclined, they are called ascending or descending, according to the direction of their inclination.

The galleries and branches of a system of mines, forming part of the defences of a fortress, are usually revetted with masonry: their construction and detail will not be included in this part of the subject, but will be explained in describing the System of Permanent Defensive Mines,' (Part IV.)

*This mode of attack was prior to the invention of globes of compression.-Editors.
By Col. Wynne, R. E.

This part is based upon the practical course taught at Chatham.-Etitors.