24 Pr. charge 8 lbs. the eprovette mortar giving 125 fathoms, the initial velocity is 1425 feet per second; with the eprovette at 90 = 1209 feet; with a charge of 12 lbs. and the eprovette at 125° the initial velocity will be 1530.
| Charge. | Eprovette. | Velocity. | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 16 | pr. | 5 | lbs. | 125 | 1415 | |||||||
| 16 | pr. | 8 | do. | 1510 | ||||||||
| 12 | pr. | 4 | do. | - | long guns | - | 1520 | |||||
| 8 | pr. | 2 | ¹⁄₂ | do. | 1418 | |||||||
| 8 | pr. | 3 | do. | 1460 | ||||||||
| 4 | pr. | 1 | do. | 1335 | ||||||||
| 4 | pr. | 1 | ¹⁄₂ | do. | 1508 | |||||||
| 12 | pr. | 4 | do. | - | field guns | - | 1442 | |||||
| 8 | pr. | 2 | ¹⁄₂ | do. | 1422 | |||||||
| 4 | pr. | 1 | ¹⁄₂ | do. | 1446 | |||||||
| 8 | inch how’r. | 1 | do. | 390 | ||||||||
| 8 | inch how’r. | 1 | 2 | oz. | do. | 516 | ||||||
| 6 | inch how’r. | 1 | do. | 532 | ||||||||
| 6 | inch how’r. | 1 | 12 | oz. | do. | 704 | ||||||
VENT, (Lumière, Fr.) in artillery, or, as it is vulgarly called, the touch-hole, is the opening through which the fire is conveyed to the powder that composes the charge.
As the placing the vents in mortars, howitzers, and guns in the best manner, is so very delicate a point, and about which both authors and practitioners differ, we will advance what the result of experiments has demonstrated. The most common method is to place the vent about a quarter of an inch from the bottom of the chamber or bore; though we have seen many half an inch, and some an inch from the bottom. It has always been imagined, that if the vent was to come out in the middle of the charge, the powder would be inflamed in less time than in any other case, and consequently produce the greatest range; because, if a tube be filled with powder, and lighted in the centre, the powder will be burnt in half the time it would be, were it lighted at one end. This gave a grounded supposition, that the greater the quantity of powder which burnt before the shot or shell was sensibly moved from its place, the greater force it would receive. To determine this, the king of Prussia, in 1765, ordered that a light three pounder should be cast, with three shifting vents, one at the centre of the charge, one at the bottom, and the other at an equal distance from the bottom and centre one; so that when one was used, the others were effectually stopped. The gun weighed 2 cwt. 1 qr. 20 lb.; its length was 3 feet 3 inches, and the bottom of the bore quite flat. It was loaded each time with one fourth of the shot’s weight; and it was found, that when the lowest or bottom vent was used, the shot went farthest, and the ranges of the others diminished in proportion as they were distant from the bottom. The piece was elevated to 1 degree 30 minutes.
In 1766 the same monarch caused several experiments to be tried with three small mortars of equal size and dimensions, but of different forms in their chambers; each of which held seven ounces and a half of powder. From these experiments it appeared, that the concave chamber produced the greatest ranges, and that the bottom of the chamber is the best place for vents, having in that place the greatest effect.
The vents of English guns are all ²⁄₁₀ of an inch diameter. See [remark 9] of the article [Velocity].
Vent-field, is the part of a gun or howitz between the breech mouldings and the astragal.
Vent-astragal, that part of a gun or howitzer which determines the vent-field.
Vent, Fr. That vacancy which is occasioned by the difference between the calibre of a piece of ordnance, and the diameter of its ball. See [Windage].
Vent, Fr. Wind. The French use this word in various senses.