IMPROVEMENTS IN COMPASSES OR INSTRUMENTS FOR MEASURING AND INDICATING THE DIRECTION OF PLACES OR ROUTES, AND FOR SURVEYING PURPOSES GENERALLY
Year: 1877

page_text: PROVISIONAL SPECIFICATION left by Edward Griffith Brewer at the Office
of the Commissioners of Patents on the 26th July 1877. (A communication
from abroad by Pierre Joseph Betboy, of Paris, France.)
EDWARD GRIFFITH BREWER, of Chancery Lane, London.
"IMPROVEMENTS IN
COMPASSES OR INSTRUMENTS FOR MEASURING AND INDICATING THE DIRECTION OF
PLACES OR ROUTES, AND FOR SURVEYING PURPOSES GENERALLY." (A communi-
cation from abroad by Pierre Joseph Betboy, of Paris, France.)
The compass is essentially composed of a box which may be square, with two
movable alidades on the compass card or compass, properly so called, divided into
360 degrees, oscillating on a style or pivot; a fixed index being placed in the axis of
the side bars serves to ascertain the direction of the route or of any other object
desired to be taken. On the opposite side of the box a regulating level is placed,
which determines either by means of a plumb line or by a pendulum the angle
which forms the altitude of a point with the horizon.
The side bars of the alidade are, according to the operation desired to be effected,
accordingly adjusted.
The manner of operating with the instrument is very simple; before arriving on
the place of operation the sheet of paper on which the operations are to be indicated
should be divided into degrees, and fixed with a little guin or a pivot; if. from a
fixed point it is desired to obtain the route up to another fixed point, the disc of the
compass is released, the side bars raised, and the alidade directed on the axis of the
route, the index will shew the degree of direction, say, the 360th, admitting that the
distance from one point to the other point is 300 metres. This distance will be
graphically carried in a direction parallel to the pivotted needle, which should be
placed upon the degree that the compass indicates; then if from a point, call it B,
it is desired to obtain successively the direction of the routes, call them C, D, E, the
operation will be similar; if for example the index shews that the route C is in the
direction of the 270th degree, the pivotted needle should be placed upon the degree
indicated by the compass; then the route is graphically carried in a direction parallel
to the pivot needle; if the route D has the direction on 320th degree it will also be
carried in a direction parallel to that degree, and so on. Operating in this manner,
Duinn A171

page_text: figures similar to those of the earth or the position to be surveyed can be obtained
with the greatest exactitude, and without any loss of time for measuring the angles,
then to bring them on to the paper by means of a regulator, as is necessary to be
done when using a graphometer or with an ordinary compass. Neither will there be
any necessity with this compass to lose time in resetting it, as is the case now with
an alidade board, which necessitates the placing with the greatest care the last line
traced in the direction last run; this operation occasions a loss of time, sometimes
considerable, and it is often difficult, and even in some cases impossible; besides, any
error committed in this operation will inevitably result in displacing at the time
and in the same sense all the directions of the lines which are taken after each
error.
With this improved instrument all these inconveniences disappear, the operations
are made much more rapidly than heretofore, and with greater accuracy, and that
without fatiguing the attention of the operator. The long and wearysome operations
which are obliged to be carried out to take down on paper the tortuous winding of
a river, for example, are very much reduced, while without resetting the instrument
the perpendiculars of a line parallel to the general direction of a river may be
determined.
To ascertain very approximately the altitude of a place, the trigometric
calculations may be replaced in these kinds of rapid surveys by a straight line
construction, which is prepared on the paper that is divided into degrees.
Example. If it is found by the aid of a levelling instrument that the height of
a point situated at 900 metres off forms an angle of five degrees with the horizon,
one would have to know the value of this angle, which is to graphically determine
from, say, a point C to a point H, a length equal to 900 metres (nine centimetres
when operating at a scale of 10000), and to bring a perpendicular to this line until
it comes in contact with the pivot needle placed on the 5 degree, that is to say, at
the point H, the length of this perpendicular will represent graphically the height
required, which in this hypothesis would be about 80 meters.
For military purposes this instrument will be of very great utility, either to a
troop having to search a wood or to the subaltern cavalry officers sent on in advance,
and who often from this fact are liable to lose their way, even the most intelligent,
and that perhaps just at a time when they have some most important particulars to
bring to a general who may be waiting for them.
In order not to miss one's way in a forest it is sufficient to divide by 360° the
card which you have, if that is not done already, care being taken to trace the 360th
as nearly as possible towards the north, and to set the pivot needle at the centre
by means of a little gum or pin, then entering the wood to take note by means of
this instrument of the degree on which it is directed, and the time occupied in
moving in this direction.
Example. By marking on the card the point of departure, admitting that you
have walked for 3/4 of an hour in the direction of 20 degrees, 1/2 an hour in the
direction of 330, an hour in the direction of 90, an hour and half in the general
direction of 280 degrees; if after these three hours and three quarters walking it is
desired to ascertain what position on the card you are, it will be then sufficient to
trace with pencil the distances which it is believed you have walked, placing them
parallel to the degrees on which you have gone; by this means you will ascertain
very approximately on what point of the card you are; then if from that it is desired
to move in another direction, the two points have only to be connected by a straight
line; to find out by means of the pivot needle to what degree it is parallel, then with
the instrument to direct it on this degree.
By practice these results are easily obtainable, and which are of the greatest
importance for a troop which has to march in a covered country.
A modified arrangement is as follows:-The same box is preserved, but the side
bars of the alidade are dispensed with, for which two apertures are substituted,
which, formed in the box, then cover the half of the surface of the dial of the
compass by a silvered (etainée) glass, a hinged frame is also provided containing

page_text: inside a silvered glass in which there is a part reserved which is not lacquered. The
image or the object to be obtained is reflected on this glass, which will reproduce
it on another, and thus by the reflection of the objects by means of the silvered
glasses it can be ascertained on the dial, the angles and the positions required for
such or such part of the horizon; this arrangement may be employed independently
o the other arrangement.
The Invention is susceptible of inodifications without departing therefrom as to
the forms, sizes, and materials employed.