IMPROVEMENTS IN THE CONSTRUCTION OF HYGROMETERS.
Year: 1875

page_text: LETTERS PATENT to Peter Jensen, of 89, Chancery Lane, in the
County of Middlesex, for the Invention of "IMPROVEMENTS IN THE
CONSTRUCTION OF HYGROMETERS.'
"_A communication from abroad by
Wilhelm Klinkerfues, Doctor and Professor, and Superintendent of

page_text: consisting of human hair, as by far the most perfectly even and homo-
geneous for the purpose is employed, and so that the expansion or
contraction of the same by the amount of humidity which the said
threads are exposed to, shall cause more or less torsion of the threads,
the influence of expansion or contraction caused by temperature being
at the same time compensated for.
I will now describe an instrument constructed according to this In-
vention.
'
On a bed plate resting on feet consisting of set screws for facilitating
the level adjustment is fixed a gallows, which is made with some
suitable temperature compensating arrangement; the gallows may for
this purpose consist of a foot on to which is erected a hollow metallic
column, to the upper end of which is fixed an internal descending
metallic tube or column, to the lower part of which is fixed an internal
ascending solid or hollow metallic post which forms the post of the
gallows proper. The gallows carries a bracket in which two small
blocks can slide, and by means of a regulating right and left hand screw
passing through them can be adjusted as to their distance apart. Each
block has a hook for attaching the upper end of one hair thread. The
lower ends of these hair threads are attached to two hooks on the centre
part of a therein suspended staff, the left-hand thread at the front and
the right-hand thread at the back; the staff has at one end a segment
piece graduated into 100 parts; from the lower part of the staff
are suspended two shorter hair threads which pass down to two small
· blocks which can slide in a bracket and are adjustable, as to distance
apart, by means of a right and left hand regulating screw passing
through them; the left-hand thread passes from the back of the central
part of the staff, and the right-hand thread passes from the front of the
said central part. Any expansion by humidity will thus cause the staff
to swing to one side in a horizontal plane, and tlie amount is indicated by
the division on the scale which comes opposite a hole or mark in a glass
bell placed over the whole apparatus; this bell has a hole at the top
which is closed by a stopper when the instrument has to be adjusted at
first starting or setting, which is done by placing chlor-calcium inside
the bell, and when the air thereby has become dry the zero of the staff
is placed opposite the hole or mark in the bell, the threads having been
put into proper tension by the regulating screws.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Peter Jensen in the Great Seal Patent Office on
the 15th July 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, PETER
JENSEN, of 89, Chancery Lane, in the County of Middlesex, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fifteenth day of January, in the
year of our Lord One thousand eight hundred and seventy-five, in
the thirty-eighth year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said Peter Jensen, Her special
licence that I, the said Peter Jensen, my executors, administrators,
and assigns, or such others as I, the said Peter Jensen, my executors,
administrators, and assigns, should at any time agree with, and no
others, from time to time and at all times thereafter during the term
therein expressed, should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the
Channel Islands, and Isle of Man, an Invention for "IMPROVEMENTS
IN THE CONSTRUCTION OF HYGROMETERS," a communication to me from
abroad by Wilhelm Klinkerfues, Doctor and Professor, and Superin-
tendent of the Royal Observatory, at Goettingen, Germany, upon the
condition (amongst others) that I, the said Peter Jensen, my executors
or administrators, by an instrument in writing under my, or their, or
one of their hands and seals, should particularly describe and ascertain
the nature of the said Invention, and in what manner the same was
to be performed, and cause the same to be filed in the Great Seal
Patent Office within six calendar months next and immediately after the
date of the said Letters Patent.
NOW KNOW YE, that I, the said Peter Jensen, do hereby declare
the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by
the following statement, reference being had to the accompanying
Drawings, and to the letters of reference marked thereon, that is to
say:―
Heretofore no hygrometer has been introduced which to the general
public offered advantages like the barometer. The Saussure hygrometer

page_text: in which the human hair is employed offers, in that respect, the greatest
advantage because of the regularity and sensitiveness of that hygroscopic
body, but the general construction of the apparatus is defective, thus,
for instance, the hair shifts in course of time on the spindle of the
"hand," the scale has to be divided for cach instrument, and the
journal friction of the spindle retains a certain influence in spite of
the greatest care and expense in the make.
According to this Invention, which has already been tested some time,
a double-threaded arrangement of some suitable hygroscopic body, but
by preference the human hair, is made use of; but the construction is
otherwise quite different from the Saussure hygrometer, and is based on
the application of a double thread suspension of a- body similarly to the
mode which Gauss employed to measure variations in the intensity of
the earth.magnetism. In the course of his experiments the Inventor
found that owing to a pecular hygroscopic property of the human hair,
as to alteration in volume, an instrument could be constructed so as to
be independent of corrections-by normal hygrometers, and so as to form
a normal hygrometer itself, and the influence of temperature was at the
same time compensated for. Gay-Lussac found that the scale of the
Saussure hygrometer corresponded to the following relative moisture of
the air at a mean temperature,
•

page_text: is inversely proportional to the square of sin. (0°.400 p + 20°.68). (It
appears that the supposition is right that this property applied to a
whole class of hair, but that the numerical co-efficient is different in
different classes.) This formula entails a fault in a little used part of
the scale amounting to 1:61 %, but this is. so small as to be immaterial,
except for very minute scientific investigations.
And in order that this Invention may be more clearly understood, I
will proceed to describe the same, with reference to the accompanying
Drawings, of which Figure 1 is a side elevation of the apparatus;
Figure 2, vertical section; Figure 3, plan; Figure 4, horizontal
section on the line X, Y, Figure 2; and Figure 5, shews the position of
the points of attachment of the hairs on the indicating bar.
s is a bar suspended in double hair threads f, f, f', f', from the
hooks, ¹, at the top, and the hooks j, j', below the bar s, see Figure 5,
the other ends of the hairs are fastened to the looks on the four
blocks˜m, m³, n, n¹, which by means of the right and left hand screws m
and N can be shifted closer together or further apart, and thereby the
torsion can be regulated; the pinion S actuating the rack B may also be
used for regulating the amount of tension, or a screw or equivalent
means may be used for this purpose. The whole is at the top suspended
from the gallows I which is arranged with some compensating appliance,
as shewn.
The bars carries at one end a paper scale corresponding to an
arc of 40° divided into 100 degrees. The case or bell H has an opening o
through which the degree of the scale opposite it can be observed, or if.
the bell is of glass a mark may answer the same purpose as a hole. The
point o is at an angle of 4°.32 to the line, at right angles to the gallows,
see Figures 3 and 4. The bell H is usually open, but may be closed at
the top by a stopper H for the purpose of regulation; the air in the
bell H is for that purpose deprived of its moisture by placing a small
saucer with chlor-calcium inside. The whole apparatus rests on three
screw feet for levelling it.
The positions of rest towards which the opposing torsions tend must
be vertical to one another. Let be the lower angle of torsion and
90° the upper angle of torsion, then the direction power of the latter
may be expressed by c¹ sin. z, and of the former by c cos. z, when c¹
and c represent the maximal values of these powers.

page_text: แน UVB
C
If of
from some reason, say through the influence of humidity on the
hygroscopic threads, suffered a little variation
so as to become
c¹
с
+8, then the angle of torsion
C
would in proportion thereto
C¹
become, and cotg. ( + d ) ===
C
+ 6 or considering the
minuteness of ô ≈ we get ô z =
8
sin.
The values c¹ and c depend according to the laws of torsion partly on
the length and distance of the two threads in a pair of threads, the
variation or increase is lience to be considered as a function of the
enlargements of the threads by humidity, and as a linear function, con-
sidering the smallness of these values. We may therefore put,-
-
in which the co-eшicients refer to human hairs.
=
By regulation of the tension of the length or of the width of double
threads the constant may be made 0.400. When this is done and the
following equation holds good for some one position in the state of
equilibrium corresponding to the angle of torsion and to the relative
humidity p, and obtained by alterations in the proportion of the two
torsions, videlicet,―
2)
zo = 0°.400 po + 20°.68,
then the following equation holds good throughout the whole scale of
relative humidity, videlicet, = 0°.400 p + 20°.68, for in consequence
of the equation 1) po being put for p=0.400 p, the condition 2)
8
is hence also fulfilled for the nearest values to zo and po, videlicet, for
≈0 + à ≈, po +p, and the conclusion arrived at must be repeated

page_text: throughout the whole scale. Contrariwise, when the condition 2) has
been fulfilled for two, say for the extreme, points on the scale of
humidity, videlicet, p = 0 and p = 100, then it is an indication that
has become = 0.400.
―
Care must be taken that in dry air = 20°.68,
and in saturated air = 60°.68, and if the per-centage increase of the
relative humidity is indicated when the bar s plays against a scale of 40°
divided in 100 equal parts, the setting point corresponding to z = 20°.68
or when the bar is put vertically to the first position == 45°.00 -20°.
-
throughout the whole scale. Contrariwise, when the condition 2) has
been fulfilled for two, say for the extreme, points on the scale of
humidity, videlicet, p = 0 and p = 100, then it is an indication that
has become = 0.400. Care must be taken that in dry air ≈ = 20°.68,
and in saturated air = 60°.68, and if the per-centage increase of the
relative humidity is indicated when the bar s plays against a scale of 40°
divided in 100 equal parts, the setting point corresponding to = 20°.68
or when the bar is put vertically to the first position = = 45°.00 -20°.
68 20,00 = 4.32.
The sensibility of the apparatus, or generally the amounts of torsion,
may most conveniently be altered by bringing the threads at one end
closer together or further apart.
1
When the double threads are not parallel but form a trapezium with
the points of suspension and attachment, the, double thread torsion
is proportional to the product of the two parallel sides of the tra-
pezium.
'
When the regulation is done by means of screws, then the alteration
in the value of the co-efficient of torsion is proportional to the amount
of turning of the screw. It is also necessary when setting the instru-
ment to alter the tension of the threads by means of a screw, which
alters the vertical position of the attachment piece for the upper, or by ·
preference the lower threads; the same screw can put the threads
altogether out of tension in order to stop the bar; in this state the
apparatus may be transmitted. In order to adjust it again a saucer con-
taining chlor-calcium is placed on the bed plate P, which is put level by
means of the set screw feet, then put the bell H over it and increase
gradually by means of the screw S the tension of the threads so far,
that with the gradual drying of the air
bar & comes to the zero of the scale.
by observing the number of pendulous vibrations of the bar s for several
minutes in perfectly dry air by means of the second hand of a
watch.
within the bell the hand of the
The same tension can be refound
When putting up the apparatus in another place chlor-calcium is
placed on the plate P, the bell Ḥ placed over it, and the tension of the
threads regulated till the hand points to zero in the perfectly dry air, or
what is better still till the bar & shews the proper number of pendulous
vibrations.
8

page_text: .
And having thus fully described the nature of this Invention, and the
mode of carrying out and applying it practically, I declare that I
claim,―
First. The double-threaded suspension in human hairs of a hand or
indicator for the purpose of a normal hygrometer with constant scale,
all substantially according to the laws and principles herein-before set
forth and as described, with reference to the annexed Drawings, whether
the hand or indicating bar be placed parallel with or vertical to the
plane of the upper and lower place of attachment.
Second. The application of the within-described and shewn apparatus
as a hygrometer, the said apparatus consisting mainly of a bar suspended
in four hygroscopic bodies arranged in pairs, the bar being kept in
equilibrium against an are of 40 degrees divided into equal parts by
means of the two opposing torsions of the two upper and the two lower
hygroscopic bodies, all constructed and operating substantially as herein 1
described and shown.
In witness whereof; I, the said Peter Jensen, have hereunto set
my hand and seal, this Fourteenth day of July, in the year.
of our Lord One thousand eight hundred and seventy-five.