IMPROVEMENTS IN SELF-RECORDING THERMOMETERS
Year: 1879

page_text: LETTERS PATENT to Hubert Airy, M.D., of Kidbrook Grove, Blackheath, in
the County of Kent, for the Invention of "IMPROVEMENTS IN SELF-RECORDING
THERMOMETERS."
"
PROVISIONAL SPECIFICATION left by the said Hubert Airy at the Office
of the Commissioners of Patents on the 15th September 1879.
HUBERT AIRY, M.D., of Kidbrook Grove, Blackheath, in the County of Kent.
IMPROVEMENTS IN SELF-RECORDING THERMOMETERS."
This Invention has for its object improvements in self-recording thermometers.
The improvements are illustrated in the Drawing hereunto annexed.
I fix a bulbed tube A, B, containing mercury in a cradle C of suitable shape,
which is balanced on horizontal pivots on a fixed frame or stand D. The cradle C
carries a small frame E suspended by a cord or cords lying in a grooved are or
arcs F concentric with the pivots of the cradle. The frame E is balanced by a
counterpoise G similarly suspended on the opposite side of the pivots. This small
frame carries a tubular glass pen H, slightly balanced with a counterpoise I. The
small frame also carries a suitably shaped rod of glass or other material K, depending
and partly immersed in oil or other fluid contained in a vessel L. (Or the small
frame E is attached below to a delicate spring.)
The pen lies horizontal, and its point is in light contact with the surface of a
scroll of paper or other suitable material M, to which a slow continuous movement
past the pen is imparted. The paper or other material may for this purpose be
wound around a vertical cylinder, or wound around and stretched between two
vertical cylinders N. The cylinder or cylinders are connected, or not, with the
fixed frame D which carries the cradle C, and are made to rotate by clockwork O;
or other means may be adopted for giving a slow travelling movement to the paper
or fabric.
The instrument operates thus,-
When the temperature of the air rises the mercury in the bulb B expands and
edvences further along the tube A. This advance of the mercury disturbs the

page_text: equilibrium of the tube and cradle, and the projecting tube A declines, and in doing
so raises the pen-frame E until the balance is restored by the lifting-up out of the
oil (or other fluid) of a sufficient length of the suspended rod K which is attached
to the pen-frame (or by the strain of the delicate spring). The pen all the time is
tracing a line on the scroll of paper as it travels. This line therefore ascends when
the temperature rises, and by a converse process descends when the temperature
falls, and so leaves a permanent continuous record of changes of temperature.
The ink or other fluid in the pen is mixed with glycerine to prevent too rapid
drying.
The paper is suitably spaced for intervals of time and for range of temperature.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Hubert Airy in the Great Seal Patent Office on the 15th March
1880.
HUBERT AIRY, M.D., of Kidbrooke Grove, Blackheath, in the County of Kent.
"IMPROVEMENTS IN SELF-RECORDING THERMOMETERS."
This Invention has for its object improvements in self-recording thermometers.
In the Drawings hereunto annexed I have shewn examples of self recording
thermometers constructed according to my Invention. Figure 1 shews a side view
and Figure 2 a plan of one construction. In these Figures A, B, is an ordinary
thermometer composed of a bulbed tube containing mercury. This tube lies in a
cradle C, which consists of two blocks of wood hollowed to receive the bulb
and united by brass side plates. This cradle is held in any desired adjustment in
an outer cradle D by four side screws E. The outer cradle D rests by knife edge
bearings on supports K, K, and has at each end a pair of grooved arcs concentric
with the pivot bearings. The front pair of arcs supports a pen frame F by parallel
cords of silk; the opposite pair supports a counterpoise I. To the toe of the pen
frame is suspended a rod of glass or ivory of suitable dimensions, partly dipping
into a vessel of oil L.
H is a pen holder, carrying, preferably, a tubular glass pen; it is hinged to the
frame F and counterpoised by weighted arms G, G, so that the point of the pen
may bear lightly against the surface of a scroll of paper or other suitable material
wound around a cylinder J. This cylinder and the clockwork arrangement shewn
as being used for giving to it a slow continuous revolving movement are the same
as in self recording barometers, so that it is unnecessary to give any description of
them. Any other suitable arrangement of mechanism might also be adopted for
causing the paper or material to travel slowly past the pen. The inner cradle C
carrying the thermometer tube- should be adjusted within D so that there shall be
nice equilibrium about the knife edge bearings. The elevation shewn at Figure 2
is drawn on the assumption that the cylinder J is made hollow at top so that the
lever arm in extreme positions can dip into the hollow. In cases where this cannot
be done the lever must be placed higher, but it is desirable to keep it as low as
possible. The bulb of the thermometer should be free in the greater part of its
length to allow free access of air. If the divisions on the temperature scale marked
on the paper are uniform the sides of the immersion rod are not made straight but
have a double curvature, as shewn, and require to be shaped carefully. In some
cases a delicate spring might be substituted for the immersion rod and oil vessel.
At Figures 3 and 4 I have shewn a modified construction of the self recording
thermometer.
In this construction in place of making the tube straight throughout I make it
bent, as shewn in the plan view, Figure 4, the end portion of the tube being hori-
zontal and parallel with the axis of the cradle. The immersion rod is not suspended
from the pen frame but from an arm M rigid with the cradle, and the point of
suspension M' is made to lie in the plane which passes through the axis of the
cradle and the end portion of the thermometer tube. The plunger or immersion rod
also is not made as a simple single rod but is formed with two branches, each branch
being an arc of a circle of the same diameter as the circle described by the extremity
of the arm M. In this way the scale of the temperature curve traced on the
travelling paper can more readily be made uniform throughout the whole range of
temperature that the instrument is adapted to record. The actual dimensions of
the scale would depend on the thickness of the plunger branches and the distance
of the point of suspension M' from the axis of the cradle. With this construction
equal increments of temperature causing equal increments of weight in the bent

page_text: part of the thermometer tube will cause equal differences of angular position of the
cradle, because thereby equal portions of the plunger branches will be raised out of
the fluid. When the line between M' and the end portion of the thermometer tube
is horizontal the centres of the circles of which the plunger branches are arcs should
lie in the plane of the surface of the fluid.
Having thus described the nature of my Invention and the manner of performing
the same I would have it understood that I claim, the construction of self recording
thermometer's, substantially as hereinbefore described.
In witness whereof, I, the said Hubert Airy, have hereunto set my hand
and seal, this Ninth day of March, in the year of our Lord One thousand
eight hundred and eighty.