A NEW METHOD OF DETERMINING THE VELOCITIES OF ROTATING BODIES, SUCH AS WHEELS AND AXLES OF MACHINERY, AND FOR CERTAIN PARTS OF THE APPARATUS USED IN THAT METHOD
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by George Sydenham Clarke and
Herbert McLeod at the Office of the Commissioners of Patents on the
21st November 1876.
GEORGE SYDENHAM CLARKE, of Cooper's Hill, Staines, Lieutenant in Royal
Engineers, and HERBERT MCLEOD, of Cooper's Hill, Staines, Professor of Natural
Science. "A NEW METHOD OF DETERMINING THE VELOCITIES OF ROTATING
BODIES, SUCH AS WHEELS AND AXLES OF MACHINERY, AND FOR CERTAIN PARTS OF
THE APPARATUS USED IN THAT METHOD."
The object of this Invention of a new method of determining the velocities of
rotating bodies, such as wheels and axles of machinery, and for certain parts of the
apparatus used in that method is to determine the revolutions of wheels, axles, and
other like articles at once without counters or indexes simply by the optical effects
based upon the following principle: If a body vibrating with a constant period is
so placed that its vibrations are at right angles to the direction of motion of a circle
of moving dots spaced round a revolving drum, cone, or disc or band, and if this
body is provided with a lens slit or other aperture through which the moving dots
can be viewed, then the combinations of the rotatory and vibrating motion will
produce upon the retina of the observer the appearance of a wave line. If the
period of vibration bears certain fixed relations to the periods in which the dots pass
in front of the vibrator, this wave line or curve will be stationary, and any change
in the velocity of the moving dots will be made instantly visible to the eye by the
wave line ceasing to be stationary. Hence it is possible to place round a disc,
drum, band, or cone rings of dots at equal distances in each ring, but differing in
successive rings, and out of which rings the vibrator is able to select that which
bears a fixed relation to its own period, it is therfore only necessary to be able to
ascertain which ring is giving the stationary curve, and the velocity of the rotation
can thus be obtained.
If the rings of dots are infinitely near to each other curves are obtained, and
portions of these curves viewed through a narrow aperture act as rings of dots.
By ascertaining at what portion on the drum, cone, discs, or band, a stationary
curve is obtained the speed of rotation can be deduced.
A mirror may be used with the vibrator, and then the vibrator must be so

page_text: arranged with respect to the rotation that the image moves at right angles to the
direction of the rotation.
Exactly analogous phenomena are obtained by using a rotator of constant known
speed, which gives a fixed number of views of the rotating dots per minute; a
familiar example of such an instrument is the well known thaumotrope, which if a
constant and known velocity could be given to it might replace the vibrating body,
and serve as the instrument with which to view our rotating rings of dots, marks,
symbols, or perforations, which dots, marks, symbols, or perforations will appear to
be at rest when the velocity of the standard rotator bears certain ratios to that of
the variable or unknown rotator, but the difficulty of making such an instrument
with a known and constant velocity makes us prefer a constant and known vibrating
body, such for example, as a tuning fork, but we are not aware that such an
instrument as the thaumotrope has been applied in any way practically for measuring
velocities.
Having now explained the principle of our method and the special new apparatus,
rings of dots or marks spaced off or infinitely near to each other, so as to form
lines or curves either by white on a black ground, or the reverse, or by any
such combination of colours as may seen most suitable, or by perforated holes
through a disc for transmitting the light used in that method, it is obvious that
the principle may be used, and the apparatus mentioned be modified in several ways,
as thus,
For the vibratory body we use preferably a tuning fork of any form or pitch,
but a reed or vibrating body with suitable requirements may in many cases answer
equally well.
For attaching to the tuning fork or other vibratory body and for viewing the
velocities of the rings of dots, we prefer a slit or aperture in a piece of metal or
other suitable material attached to one arm of the tuning fork, though we may use
a lens or combination of lenses, a mirror or mirrors, for conveying the image to the
desired position for inspection or any convenient combination of two or more of these
instruments or means.
The revolving body may have attached to it a drum, cone, disc, or rod, which
may be provided with dots, lines, curves, slits, perforations, or other apertures.
A moveable screen may be attached to a stand with an aperture or apertures to
cut off any portion of the revolving image.
A large lens or combination of lenses may be used in connection with the fork.
An eye piece may be employed in connection with the fork or reed to avoid
parallax.
A graduated scale may be employed either of glass, paper, metal, or wood, which
in connection with the apparatus may be used to read off the revolutions of a shaft
wheel or axle at sight.
Mechanical arrangements, sliders, racks, and pinions or endless screws, may be
used for adjusting the relative positions of the vibrating body, the eye piece, or the
screen, in each or all cases, as the several requirements of the velocities to be
ascertained are needed.
As illustrations of the manner of using some of the combination we mention
these,―
1st. The drum, cone, disc, band, or rod to be driven by an engine or other means,
and the velocity of which is to be determined, is provided with the drum, cylinder,
or disc of dots, lines, curves, slits, or perforations. The fork or vibrating body is
fixed or held in front of the revolving body, and the shifting screen is placed
between this and the fork when required. The image of the revolving dots, curves,
slits, or other marks is now viewed through the slit attached to the vibrating body
or through a lens attached thereto, or on a mirror. Where the scale is required it
is placed in front of the vibrating body, so as to be unaffected by its vibrations,
and may be attached to the motion for traversing the screen in such a way that the
position of the screen when the observation is made can be ascertained, and the
velocity made known.

page_text: 2ndly. Another form of the apparatus would consist of the fork or reed adjusted
to be moved in front of the revolving body by a slide rack or screw motion.
Successive portions of the drum, cone, or disc, would then be brought into view by
the motion of the vibrating body. An eye piece will then be required, moving with
the vibrator so as to avoid parallax.
In either case the velocities may by a mechanical arrangement be readable on a
dial near to or at a distance from the observer.