See _Sound_.
IX. The following simple micrometer may be so usefully applied
to military purposes, that I shall extract it verbatim from the
Philosophical Transactions for 1791, where it is described by Cavallo.
This micrometer consists of a thin and narrow slip of mother of
pearl, finely divided, and placed in the _focus_ of the eye glass
of a telescope, just where the image is formed.—It is immaterial
whether the telescope be a reflector, or a refractor, provided the eye
glass be a _convex_ lens and not a _concave_ one, as in the Galilean
construction.—The simplest way to fix it, is to stick it on the
diaphragm, which generally stands within the tube, and in the focus of
the eye glass.—When thus fixed, if you look through the eye glass, the
divisions on the scale will appear very distinct, unless the diaphragm
is not exactly in the focus; in which case the scale must be placed
exactly in the focus, by pushing the diaphragm, backwards or forwards,
when this is practicable; or else the scale may be easily removed
from one surface of the diaphragm to the other, by the interposition
of a circular bit of paper or card, or a piece of sealing wax.—This
construction is fully sufficient when the telescope is always to be
used by the same person; but when different persons are to use it, then
the diaphragm, which supports the micrometer, must be so constructed
as to be easily moved backwards or forwards, though that motion need
not be greater than about the tenth or eighth of an inch. This is
necessary, because the distance of the focus of the same lens appears
different to the eyes of different persons; and therefore whoever is
going to use the telescope for the mensuration of an angle, must first
unscrew the tube which contains the eye glass and micrometer, from the
rest of the telescope, and, looking through the eye glass, place the
micrometer where the divisions of it may appear most distinct to his
eye. The mother of pearl scale may be about the 24th part of an inch
broad; its length is determined by the aperture of the diaphragm; its
thickness that of writing paper. The divisions on it may be the 200th
of an inch, which may reach from one edge of the scale to about the
middle; and every fifth and tenth division may be a little longer,
the tenths going quite across. When the telescope does not magnify
above 30 times, the divisions need not be so minute. For the sake of
those not conversant in trigonometry, the following is an easy method
of determining the value of the divisions on the scale. Mark upon a
wall or other place, the length of 6 inches; then place the telescope
before it so that the 6 inches be at right angles to it, and exactly
57 feet 3½ inches distant from the object glass of the telescope. This
done, look through the telescope, and observe how many divisions of the
micrometer are equal to it, and that same number of divisions will be
equal to half a degree, or 30´; and this is all that need be done to
ascertain the value of the scale. The reason on which it is founded is,
that an extension of six inches at the distance of 57 feet, 3½ inches,
subtends an angle of 30´, as is easily calculated by trigonometry. To
save the trouble of calculation, a scale may be made requiring only
inspection. Thus, draw a line equal to the diameter of the field of the
telescope, and divide its under side into the same number of parts as
are on your micrometric scale, and, by the above operation on the wall,
having determined the value of 30´, which we will suppose to correspond
with 16 divisions on the scale, mark 30´ on the opposite side of the
line, opposite 16 on the lower; 15 opposite 8, and so on.
By the following table the results may be ascertained by inspection
only: thus, suppose an extension of 1 foot is found by the table to
subtend an angle of 22′, the distance will be 156.2: and suppose at the
distance of 171.8 an object subtends an angle of 20′, its height will
be found to be 1 foot; or, suppose an object of 6 feet high to subtend
an angle of 20′, the distance is 1030.8, by multiplying 171.8 by 6.
_Table of Angles subtended by 1 Foot, at different Distances._
+--------+------------++--------+------------+
|Minutes.| Distances ||Minutes.| Distances |
| | in feet. || | in feet. |
+--------+------------++--------+------------+
| 1 | 3437.7 || 31 | 110.9 |
| 2 | 1718.9 || 32 | 107.4 |
| 3 | 1145.9 || 33 | 104.2 |
| 4 | 859.4 || 34 | 101.1 |
| 5 | 687.5 || 35 | 98.2 |
| 6 | 572.9 || 36 | 95.5 |
| 7 | 491.1 || 37 | 92.9 |
| 8 | 429.7 || 38 | 90.4 |
| 9 | 382.0 || 39 | 88.1 |
| 10 | 343.7 || 40 | 85.9 |
| 11 | 312.5 || 41 | 83.8 |
| 12 | 286.5 || 42 | 81.8 |
| 13 | 264.4 || 43 | 79.9 |
| 14 | 245.5 || 44 | 78.1 |
| 15 | 229.2 || 45 | 76.4 |
| 16 | 214.8 || 46 | 74.7 |
| 17 | 202.2 || 47 | 73.1 |
| 18 | 191.0 || 48 | 71.6 |
| 19 | 180.9 || 49 | 70.1 |
| 20 | 171.8 || 50 | 68.7 |
| 21 | 162.7 || 51 | 67.4 |
| 22 | 156.2 || 52 | 66.1 |
| 23 | 149.4 || 53 | 64.8 |
| 24 | 143.2 || 54 | 63.6 |
| 25 | 137.5 || 55 | 62.5 |
| 26 | 132.2 || 56 | 61.4 |
| 27 | 127.3 || 57 | 60.3 |
| 28 | 122.7 || 58 | 59.2 |
| 29 | 118.5 || 59 | 58.2 |
| 30 | 114.6 || 60 | 57.3 |
+--------+------------++--------+------------+
_DRAG ROPES_—
weight length
5 pins 6 lbs. 8 oz. 21 feet.
With 4 ” 5 6 13
3 ” 5 0 12
_EMBARKATION._
1. _Of Ordnance and Stores._—The first thing necessary is to prepare a
list of all the articles to be embarked, with the weight of each. This
list must have a large column for remarks. The tonnage required for
bulky articles will be generally ⅓ more than their actual weight; but
the tonnage of ordnance, shells, shot, _&c._ will be equal to their
weight. If vessels be paid according to the tonnage they carry, the
masters will of course stow away as much as the ships will hold; but
if, by the voyage, they will be averse to loading their ships too much;
a naval officer should therefore always attend to see that the ships
are properly stowed.
Ordnance and stores may be embarked either for the purpose of merely
transporting them to another situation, or for a military expedition.
In the first case, each ship must be stowed with as much as it will
carry, and every article that relates to one particular species of
service or ordnance, must be put on board the same ship; that in case
one ship be lost, the others may remain in themselves complete. This
principle must of course be likewise attended to in an embarkation
for an expedition; but a more particular distribution must take place
of the stores when on board. With each piece of ordnance must be
placed every thing necessary for its service; its side arms, carriage,
limber, ammunition, _&c._ so as to be readily come at, when required
to be disembarked. If it be an embarkation of ordnance, _&c._ for a
siege, not only every thing necessary for the service of the pieces of
ordnance should be arranged with them; but also every thing necessary
for the construction of the battery on which they are mounted. It will
be adviseable in this case, to put different natures of ordnance in the
same ship, in proportions according to the service required of them. In
general it will be best to put the heavy articles in first, and every
thing that is light, easy to be removed, or likely to be first wanted,
on the top. Previous to embarkation, the guns, carriages, waggons,
_&c._ must be dismounted, but first numbered as follows: and the
number of each article marked in the list, in the column of remarks.
Give each piece of ordnance and its carriage the same number. Give the
ammunition and other carriages, different numbers from the ordnance
carriages. Then give every limber, whether of ordnance carriage,
ammunition carriage, or waggon, the number of its respective carriage.
If for a simple transport, arrange the small stores, side arms, _&c._
according to their several natures; but if for an expedition, every
thing belonging to each particular piece of ordnance must be collected
together, and the cases or chests in which they are put, marked with
the number of the piece of ordnance to which they belong, their natures
and description. If there be any doubt of the different parts of the
carriages, being made with that uniformity, so essentially necessary,
every part which is separated, must bear the number of its carriage.
This precaution at any rate may be a good one, if the same vessel
contain different natures of ordnance or carriages.
The axletrees need not be taken off the carriages, if the vessel be
of a sufficient size to admit them when fixed, as they are not easily
replaced without workmen and a tedious operation. When a carriage is
dismounted, all the small articles, such as elevating screws, linch
pins, drag washers, cap squares, _&c._ must be carefully collected, and
secured in a box, marked with the description of stores, and number of
the carriage to which they belong. All carriages or waggons embarked
with their axletrees fixed, must be arranged in the ship, side by side,
and alternately front and rear, that their axletrees may not interfere
with each other, and take too much room. Every transport or other
vessel employed in carrying troops or stores for an expedition, should
be numbered on the quarters and on the bows, with figures as large as
2 or 3 feet, and on the sails, that they may be known at a distance.
The number of the ship, her name and tonnage, and the master’s name
must be entered in the list of the stores which she carries.
In disembarking ordnance and stores, they must be landed exactly
in order, the reverse of what they were shipped. The carriages and
waggons must be mounted as soon as possible, and every nature must be
arranged as far from the shore as possible to prevent confusion. If the
disembarkation take place in the presence of an enemy, the vessels of
course must be loaded accordingly; and the field ordnance, with their
carriages, ammunition, _&c._ must be so arranged as to be first landed,
and with the greatest ease possible. In this case, the entrenching
tools must also be kept in the greatest readiness.—_Aide Memoire._
2. _Of Troops._—All transports taken into His Majesty’s service, are
under the direction of the Transport Board, and of their agents at the
different ports at home and abroad. No troops or other persons can be
put on board them, or victualled, but by an order from this Board, or
one of its agents. Troops embarked on board transports or ships of
war (except as marines) are only allowed ⅔ of a seaman’s allowance
of provisions. (See the word _Ration_.) It is therefore necessary to
divide the men into messes of 6 each. Six women to 100 men embarked
on foreign service, are allowed provisions; and 10 women to 100 men
on home service. The births on board transports, are usually made 6
feet square, and each admits 4 men at a time; but agreeable to the
regulations for the army for 1799, one third of the men are always to
be on deck; therefore 6 men (or one mess) are told off to each birth,
⅓ of whom are always on watch. The commanding officer of the troops on
board a transport, has a right to peruse the charter party of the ship,
which points out every different article, as firing, candles, boats,
utensils, _&c._ which the ship is engaged to find for the use of the
troops on board. It likewise expresses the part of the ship allotted to
the officers, to the master, the mate, and the agent, should there be
one on board.
_EXERCISE of Artillery._—_With 9 men to a field gun._
When 15 men are attached for the service of a gun in the field, they
are numbered from 1 to 15; but when the gun is not to be advanced by
men, the first six numbers are left out, and the remaining nine men are
numbered from 7 to 15. The exercise of field guns of a heavy nature
varies but little from the light ones. Though different duties done by
the men attached to the one, should, as nearly as possible, be kept
up at the other; as thereby is prevented that confusion which must
arise when men removed from a light gun to a heavy one, change their
numbers, though their duties at each be the same. The following will
be the position of 9 men, for field ordnance of all natures, in the