The Sun.
London, England, 1856-09-09 00:00:00

The following description of the self-registering mercu-
rial minimum thermometer,invented by Messrs. Negretti
and Zambra, of Hatton-garden, was read by Mr. Lee at
the recent meeting of the British Association at Chelten-
ham :—"The importance of a self-registering mercurial
thermometer will be duly appreciated by any one interest-
ed in meteorological pursuits, when it is remembered that
all thermometers hitherto constructed for minimum pule
poses have alcohol for the thermometrical fluid, on the plan
of Dr. Rutherford's thermometer. The unequal expansion
of alcohol at different degrees of heat has long caused a
self registering mercurial minimum thermometer to be-
come &desideratum ; for, if attained, then all thermometers
in a meteorological observatory would be constructed,
with one fluid, and that fluid the recognised standard of
heat. Impressed with :he importance of this subject,
the inventors, so far back as 1851, shortly after the in-
troduction of their patent self-registering maximum ther-
mometer, applied themselves to the task of discovering
how a minimum therinnmeter could be made to answer
the requirements of those who desired accurate self-regis-
tering instruments. Thermometers of all shapes and make
were attempted by them, and when about to abandon the
idea, after experiments of four years' continuance, the
happy thought struck them that that which, in the old
Rutherford maximum was a defect, should now with a little
modification become the new patent minimum thermo-
meter. The task of keeping
the steel index from plung-
ing into the mercury of a Rutherford maximum was the
great difficulty which parties using it had to contend
with ; for, when the index once entered the mercury, it
could not without greatdifficulty again be extracted. In
the thermometer now before us the endeavour i,, not to
prevent the index fromentering the mercury, but to add
it in doing so as much as possible ; or, rather, to assist
the mercury to pass it, which is the same thing. The fol-
lowing is an endeavour to explain the construction of
this new instrument, and then it will be better under-
stood upon what principle it is constructed. The thermo-
meter, as shown by the diagram before us, has a bulb of
rather large size, consequently it allows of a tube corre-
sponding being large in the bore for that part forming
the scale. On the surface of the mercury enclosed in the
tube is placed a small steel needle, pointed at both ends,
which forms the index ; and it may be here remarked
that it is preferable to read the temperature from the
upper end of this steel needle enclosed in the tube, and
not from the mercury itself. This conical needle will
be capable of moving freely in the bore of the tube, and,
as the mercury descends therein, will of course fall with
it, but when the mercury ascends in the tube the mer-
cury will pass the lower pointed end of the needle, and
rise above the same without raising or moving the needle.
This latter will therefore remain stationary, and, con-
sequently, its upper point will indicate the lowest
temperature to which it has descended during the
12 or 24 hours, and will not be affected by any subse-
quent rise in the temperature. To reset the thermome-
ter for any future observations, it is necessary simply to
turn it in such a position that the mercury and needle in
the tube will flow into the reservoir at top. Tkis it will
readily do, as there is no air above the mercury. Should
the needle not freely flow with the mercury into the re-
servoir, it may be assisted with a magnet, which may be
held there until, by returning the thermometer to the
upright position, the mercury flows back again into the
tube ; and then with the magnet the index may be re-
turned to the surface of the mercury ready for future
observations. One of the thermometers is now before
you, and can be examined by any one who feels inte-
rested in its success. In reply to any question that
may arise as to the probability of this thermometer
answering the purposes for which it was intended, it
may be remarked that, since November last, one has
been in the hands of the secretary of the British Meteo-
rological Society, and another at the Royal Observatory
at Greenwich, both of which have acted most accurately,
and in two instances have corrected errors in the alco-
hol minimums, which, but for it, would have passed
unnoticed. A few others have also been in use by gen-
tlemen who are well calculated to judge of their merits.
Among them we will mention Mr. E. J. Lowe, of Beeston
Observatory, near Nottingham ; also Mr. Drew, and two
or three members of the British Meteorological Society.
The inventors are fully aware that it is subject, like all
new instruments, to criticism ; but, be it perfect or im-
perfect, they present it before you as the first mercurial
self-registering minimum thermometer that has ever
been invented. Should it, however, meet with only
half the success that their patent maximum thermometer
has done, they will be highly repaid for their exertions,
as upwards of 1,400 maximum thermometers are now in
the hands of the most scientific men of this country, and
not in one instance have they signally failed."