IMPROVEMENTS IN THE METHODS OF CONSTRUCTING GALVANOMETERS
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by Roland Harry Ridout at the Office of
the Commissioners of Patents on the 25th July 1876.
ROLAND HARRY RIDOUT, of Monmouth, Science Master. "IMPROVEMENTS IN
THE METHODS OF CONSTRUCTING GALVANOMETERS."
This Invention of improvements in the methods of constructing galvanometers,
consists in so constructing them that the force of the current in the galvanometer
coil shall not be weakened by the spaces made through then for the suspension of
the needles.
In the ordinary method of constructing the galvanometer the coil if mado in one
piece is perforated on the upper portion, either by diverting the coil at the centre
after it is wound, or by winding it with a plug or mould in it, and in many cases
both the upper and lower portion of the coil is so divided, or a passage so left, or
in other cases the coil is made in two separate coils, the object in all these instances
being to leave a passage for suspending the two needles in the coil, or one in the
coil and one above or below it, the effect of these methods is this, that in all cases
the central parts of the coil which should be the most energetic are really lost.
In the methods of construction I will now describe I prevent any necessity for
disturbing the coil at this the central and most valuable portion.
I therefore construct the coil in one solid and continuous piece, and support it
in any convenient manner; within the coil on the lower surface I place a small
point on any convenient base, and on this point I suspend the magnetic needle
projecting from the centre, and at right angles to the needle are metallic or other
suitable arms, which protruding through the coil are then turned down, and when
clear of the sides of the galvanometer coil are then continued under it to the centre
where the attachment is made with the second magnetic needle forming the
necessary and usual astatic combination. The pair of needles are now combined in
a stirrup supported parallelly and horizontally, one in the coil and one below it, as
the point of suspension is in the upper part of the frame, the needles hang very
steadily though perfectly free to receive the action of the coil.
It is obvious the same method may be adopted by making the lower needle
within the coil and the upper one to rest on the pivot which will then be fixed on
the upper and superior part of the coil.
The first arrangement of the needles enables me to suspend from the centre of
the lower needle a dependent wire needle or rod, which passing through a perforated
piece of glass, agate, or suitable material, the perforation being slightly larger than
the needle and thus control the vertical oscillations of the needle so that the
[Price 2d1

page_text: instrument may be used under conditions where the ordinary instrument can only
be used under great difficulties.
The great advantages of these methods over the ordinary methods of construction
are the much greater sensibility from the fact that the coil is used intact, its
stability requiring no elaborato levelling so requisite in the ordinary torsion
instrument, and also the steady action of the instrument when the indications of
the currents are to be made visible by reflecting mirrors attached to the needles.