ss Be Bae 
S.W. Holman—Method for Calibrating Thermometers. 279 
the average error less than some specified amount.. An inspec- 
tion of these conditions will show that the calibration of such 
a tube and scale can be only approximate except with correc- 
tions for the inequalities of the spacing, involving an amount 
of labor disproportionate to the result attained. The best 
makers, such as Fastré, Baudin and others, have produced sat- 
isfactory thermometers graduated to equal volumes; but even 
these are not as reliable as instruments of less cost with a scale 
of equal linear parts, say of millimeters, supplemented by a 
calibration by the observer. The best form of tube for almost 
1 work is one backed with white enamel, with an inverted 
pear-shaped bulb at the upper end of the capillary (a very 
important feature), and with a scale of equal arbitrary linear 
parts (0°7 mm. to 1 mm. is a suitable length for estimation of 
tenths) or of approximate degrees, for convenience, etched or 
engraved upon it. 
the use of the observed freezing and boiling points, upon 
which some methods are based, is most undesirable. 
In the method which will now be given, either one or both 
of these points may be left to be selected, according to the 
combined conditions of length of thread employed, shape of 
the tube, and numerical convenience, after the observations 
with the thread have been made. 
_Let it be desired to find the calibration corrections for a 
given tube. Determinations which will give the errors of 
Set the thread with its lower end at or near the beginning of 
the graduation: call the reading* of the lower end of the 
* Tenths of a division are supposed to be read by estimation. 
