Year: 1888

page_text: I, EDOUARD EMMANUEL DE FACIEU, of Elephant Point, near Rangoon, Burmah
Clerk Eastern Extension Australasia and China Telegraph Company Limited do hereby
declare the nature of this invention and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement:-
--
This invention relates to certain improvements in the arrangement, combination and
construction of parts of galvanometers and refers more particularly to the type of
instruments known as "mirror" galvanometers.
In order that the said invention may be fully understood and readily carried into
effect I will describe the same with reference to the accompanying drawings.
Figure 1 is a sectional front elevation of a mirror galvanometer constructed
according to my invention; Figure 2 is a side elevation of a portion of the instrument
removed from its surrounding case or frame and shewing the coil, index finger, and
some other parts. Figure 3 is a detailed perspective view shewing the coil adjustment
rack, detached. Figure 4 is a detached front view of the spindle carrying pinion for
operating the coil adjustment rack. Figure 5 is a detached front view of the adjust-
able bearing for the spindle shewn at Figure 4; Figure 6 is a side elevation of the
upper end or head of the supporting bracket for carrying the filament which supports
the magnets. Figure 7 is a sectional view of the head of same drawn to a larger scale
than Figure 6.
According to my invention, the galvanometer consists essentially of a rectangular
coil A of insulated wire pivotted on a horizontal axis B on which the said coil may be
caused to revolve through an arc of 90° by an adjustment (Figures 1 and 2) consisting
of a segment rack C shewn separately at Figure 3 and a spindle (Figure 4 carrying
a pinion C² which gears into the rack C, and provided with a milled head.
An aperture D in the centre of the coil (see Figure 1) admits a centre piece con-
sisting of a fine glass tube E to which are fixed a number of small magnets F and also
a small plane mirror G, the said glass tube being suspended from the bent bracket H
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page_text: (Figures 2, 6 and 7) by a fine wire or a fibre 'J. This wire or fibre J passes through
the whole length of the glass tube E to the lower extremity where it is fixed. The
magnets F are all attached with their similar poles in the same direction, and the
whole system is controlled by a directing magnet on the top of the case similar to that
employed in the so called Sir William Thompson's mirror galvanometer.
To one of the pins B on which the coil A rotates is attached an index finger B' which
indicates on a graduated scale K the angle given to the coil see Fig. 2.
As the effect of the coil on the magnetic system, which it encloses will vary from
its full force when in a vertical position, to nil when in a horizontal position, a
table may be constructed experimentally to give the "multiplying power" of the
principal angles as compared with 0°, thus enabling the operator to dispense with the
use of a shunt. The number of the magnets F on the centrepiece may vary, but to
equalize their weight they should be affixed on alternate sides of the glass tube E, the
uppermost one being necessarily placed at the back, so as to allow the mirror G to be
fixed in front. The object of having several magnets on the centrepiece instead of a
single one, is to increase the ratio at which the sensitiveness of the galvanometer
decreases when the coil is moved from the vertical position; the length of the centre-
piece being sensibly greater than the width of the coil, it will be seen that when the
latter is at a considerable angle, the upper and lower magnets will be proportionately
abstracted from its influence and more subjected to that of the controlling magnet,
whereas they will obey the impulse of a current equally with the other magnets when
the coil is vertical. The smaller the number of magnets, the more marked will be this
result, they should not however be fewer than two. If only two magnets are used on
the centrepiece, they should, obviously, be attached to the upper and lower extremities
of the glass tube, so as to stand at equal distances from the axis of rotation of the
coil.
The bearing of the pinion spindle C' for operating the segment rack C is constructed
as shewn at Figures 1 and 5 so as to allow of being tightened, to prevent slipping of
the coil when adjusted to any angle.
The case L Figure 1 is rectangular in shape and may be removed bodily with the
directing magnet; it is provided with two apertures covered with planed glass, one on
the front and one on the side next the graduated scale.
The bed M consists of a slab of ebonite affixed to a wooden bed. The ebonite slab
is provided with a circular spirit level, and the whole instrument is supported by three
levelling screws, the graduated scale being so adjusted that on the instrument being
levelled, the coil is at its position of greatest power with the index at 0°. Only two
terminals are required.
The great length of the fibre obtained by the herein described arrangement and
construction of instrument tends to render it comparatively more sensitive than hereto-
fore. In order to prevent chafing of the fibre at the upper extremity of the glass
'tube, the latter should be brought near a flame, until the roughness of the edges has
disappeared, a platinum wire being inserted to keep the tube from closing; in 'practice
I have found that the glass tubes used in the "Siphon Recorder answer well for this
'purpose.
""
The small magnets F should preferably not exceed about inch in length, and the
central aperture D of, the coil A should be of sufficient width to allow the spot of
light from the mirror G to travel freely on a 2 foot scale which is preferably used
with this instrument; this scale may conveniently be similar to the patterns in present
use.
3
Having; now, particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed I declare that what I
'claim is :-
1. In galvanometers, the arrangéinent and combination of parts consisting of 'the
coil A on horizontal axis B, and having an aperture D, the bracket H, the fibre or
wire J, the glass tube E, magnet F and mirror G all substantially as and for the
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page_text: 2. The construction, arrangement and combination of parts composing my improved
galvanometer as hereinbefore described consisting of the coil A on axis B, aperture D,
bracket H, fibre J, glass tube E, magnets F and mirror G together with the adjust-
ment device C, C, C², finger B¹ and scale C, the case or cover L and parts connected
therewith all substantially as and for the purposes described and illustrated with .
reference to the accompanying drawings.
DL
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