The daily Gate City., 1856-02-02
For the Gate City.
Therm ometers.

u
er article, to which it alludes, written pre-
vously, is omitted, as ii makes current allu-
sions now rather out Of time. II was de-
voted mainly to demonstrating the differences
in the indications Of thermometers, caused
bv their being hung against brick or wooden
walls, or in the air, the latter being considered
as the most proper method Of exposure
EDS. GATE CITY.l
MKssRs EplToRs - recently sent you o
few observations on the different errors Of
thermometers, arising from the different SIT
uations in which the instruments are placed.
But this does not explain all the differences
that are observed. Thermometers hanging
side by side, and affected by exactly the same
influences, will often differ, and show such
differences that any inequalities or inaccu-
racies in the equal division of the scale will
not account for them. At least such is the
result of my observation in several instances.
wish to say word or too now, upon fhiS
cause Of difference, and OF course error
| In these remarks, | shall be obliged to cor
rect, or, at least, run athwart very COM
mon opinion, and one expressed BY your cor
respondent from Pennington, which Of
| course regard as an error. Your correspond
! ent SAYS ''lf the points Of freezing and Of
boiling water are accurately made, and all
the degrees Of the scale made cqui-distant,
| and Of the requisite number, and all made
/ from these two points as the basis,
"sueh a Thermometer will be correct" This
| is the rule given in some of the books, and
it is undoubtedly the rule usually followed
in their manufacture, especially the cheap
er articles. This practice and this rule, are
based upon the supposition that the tubes
manufactured into thermometers, are ''uni-
/ form in their calibre.''
| But good authorities say that very few
tubes are made OF equal capacity throughout
! their entire length. Brande's Encyclopp
dia of science, Art. Thermometer, says, ''not
more than one sixth part of the tubes that
come from the glass houses, are fit for the
purpose" The Encyclopedia Americana,
Art Thermometer, saws, "The tubes drawn
al the glass houses for making thermometers,
are all more or less irregular in the bore
I Hence, If equal apparent expansions OF the
! included mercury be taken TO represent
/ equal thermometric intervals, these equa
expansions will occupy unequal spaces in an
/ irregular tube. The attached scale should
therefore, compare exactly to these tubular
! Irregularities or if the scale be uniform in
its dimensions, we must be certain that the
| tube is absolutely uniform III its calibre'
Now if the above statement, "that al
tubes are more or less irregular IN the bore,'
be trae, then it is obvious that thermometers
with exactly equal divisions Of the scale,
however accurately the cardinal points may
be taken, can never exactly agree with each
other, except in parts of the scale and the
more unequal the bore, the wider will be the
difference, unless the irregularities should be
in exactly the same relative part of the tube,
and To exactly the same extent,a thing IN
no wise supposabIe. Then, further, should
| such instruments chance TO agree together,
| they cannot by possibility agree with cor
rect one through but part of the scale. An
illustration may make this subject plain to
some minds. Suppose particular tube, in
q given part, say between the points Of 81
and IL degrees, rs marked upon scale of
equal divisions, should be enlarged SO that
in the extent of five degrees, as marked up
on the scale, It's capacity should be as great
as il ought to be in the space Of ten degrees,
then obviously. in that part the mercury
would rise or fall but FIVE degrees when It
ought to rise or fall ten degrees. In this
case too the error would be extended all the
way up the scale, to the point Of "boiling
trdter, the instrument all the way up,
would indicate too low Il temperature. SO
too, if the capacity Of the bore should be
diminished, so that in the span of 10 de-
grees ii would hold no more than it ought
70 hold in five degrees, then of course, il
would rise or fall 10 degrees when it ought to
rise or fall but FIVE. In this case too, as in
the other, the error would be extended al
the wayup the scale, to tho boiling point, and
would indicate TOO high temperat ure.
If these facts and this reasoning be cor
rect, il is obvious that the scales Of ther-
momcters should be graduated with scrupu-
lous and exact regard to the inequalities OF
the bore Of the tube. In the American En-
cyclopndia is method given, by which the
manufacturer may make such graduation,
but It's not an easy thing; it cannot be done
10 minute, without difficulty. 1t is the du-
", however, Of the manufacturer to do so
and DO It faithfully, and the faithful man
will do it. All correct instruments are made
in this way, unless perchance some may be
tested and graduated throughout their Who'll,
length, by an instrument known to be cor