A THERMC- METER OR MACHINE FOR ASCERTAINING THE HEAT OF BAKERS' OVENS, AND VARIOUS OTHER PURPOSES
Year: 1809

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, STEPHEN
HOOPER, of Walworth, in the County of Surrey, Gentleman, send greeting.
WHEREAS His most Excellent Majesty King George the Third, did, by
His Letters Patent under the Great Seal of His United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the Thirteenth day of
February, in the forty-ninth day of His reign, give and grant unto me, the said
Stephen Hooper, my exors, adñiors, and assigns, Ilis especial licence, full
power, solo privilege and authority, that I, the said Stephen Hooper, my exors,
aduiors, or assigns, should and lawfully might, during the term of fourteen
years therein mentioned, make, use, exercise, and vend, within England,
Wales, and the Town of Berwick-upon-Tweed, my Invention of "A THERMC-
METER OR MACHINE FOR ASCERTAINING THE HEAT OF BAKERS' OVENS, AND VARIOUS
OTHER PURPOSES;" in which said Letters Patent there is contained a proviso,
obliging me, the said Stephen Hooper, by an instrument in writing under my
hand and seal, to cause a particular description of the nature of my said Inven-
tion, and in what manner the same is to be performed, to be inrolled in His
Majesty's High Court of Chancery within one calendar month after the date
of the said recited Letters Patent, as in and by the same, relation being there-
unto had, may and will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Stephen Hooper, do describe and ascertain the nature, construction, and use
of my said thermometer or machine for ascertaining the heat of bakers
ovens, and various other purposes, as follow, that is to say :-

page_text: The nature or principle of my said thermometer or machine consisteth in
the comparative degree of expansion or contraction which takes place in
different substances when these substances are exposed to different degrees of
temperature, and in order to reduce this to practice and make it applicable to
the purposes above mentioned, I do construct my said machine as follows, that
is to say :-
I make use of two rods, bars, or tubes of any convenient length and shape;
and the substances of which these rods are made are such that one of them is
subject to a greater degree of expansion or contraction than the other, when
exposed to different degrees of temperature, or, in other words, I chuse such
substances that one of them may be subject to as little and the other as much
variation in length as possible when heated or cooled, possessing at the same
time such other properties as render them of convenient application. I do
therefore generally make use of brass and wooden rods, or, as being more con-
venient, a brass tube and a wooden rod, which are herein-after more particularly
described as follows, that is to say:-I make a brass tube of any convenient
length and diameter; the length of the said tube I generally make equal to
the length of the oven to which the thermometer is intended to be applied,
and about an inch and a quarter in diameter; into the said brass tube I intro-
duce a wooden rod, made of fir or any other very straight-grained wood, the
wooden rod being nearly of the same length as the brass tube, and of such a
diameter as to slide freely backward and forward in the brass tube without
sticking. The said brass tube and wooden rod are firmly fixed to each other
at one end, so that if any expansion or contraction arising from a change of
temperature takes place in the brass tube, that change of temperature will bot
indicated at the other end by the increase or decrease of the length of the brass
tube when compared with that of the wooden rod; the said rod having a scale
fixed thereon for that purpose. But as the divisions upon the said scale, when
so constructed, are too minute to be easily made or distinctly observed, I prefer
a scale with larger divisions, which I obtain by applying a lever or a combi-
nation of levers, according to the well-known methods now in uso for con-
structing pyrometers, or by a rack and pinion, in which case I affix a rack to
the end of the brass tube, and cause the said rack to turn a small pinion, and
upon the axis of the said pinion I place a hand or index, which points out the
degree of expansion or heat upon a circular plate properly divided; the said
pinion and plate in which the axis of the pinion turns are affixed to the
wooden rod.
I now proceed to describe the mode of using my said thermometer or
machine, more particularly when applied to baker's ovens, that is to say, I