the
valley behind it, with which it is connected by over 200 m. of river
navigation, a good outlet on the Pacific coast. Coal deposits exist in
the immediate vicinity of the town.

CALIBRATION, a term primarily signifying the determination of the
"calibre" or bore of a gun. The word _calibre_ was introduced through
the French from the Italian _calibro_, together with other terms of
gunnery and warfare, about the 16th century. The origin of the Italian
equivalent appears to be uncertain. It will readily be understood that
the calibre of a gun requires accurate adjustment to the standard size,
and further, that the bore must be straight and of uniform diameter
throughout. The term was subsequently applied to the accurate
measurement and testing of the bore of any kind of tube, especially
those of thermometers.

In modern scientific language, by a natural process of transition, the
term "calibration" has come to denote the accurate comparison of any
measuring instrument with a standard, and more particularly the
determination of the errors of its scale. It is seldom possible in the
process of manufacture to make an instrument so perfect that no error
can be discovered by the most delicate tests, and it would rarely be
worth while to attempt to do so even if it were possible. The cost of
manufacture would in many cases be greatly increased without adding
materially to the utility of the apparatus. The scientific method, in
all cases which admit of the subsequent determination and correction of
errors, is to economize time and labour in production by taking pains in
the subsequent verification or calibration. This process of calibration
is particularly important in laboratory research, where the observer has
frequently to make his own apparatus, and cannot afford the time or
outlay required to make special tools for fine work, but is already
provided with apparatus and methods of accurate testing. For
non-scientific purposes it is generally possible to construct
instruments to measure with sufficient precision without further
correction. The present article will therefore be restricted to the
scientific use and application of methods of accurate testing.

_General Methods and Principles._--The process of calibration of any
measuring instrument is frequently divisible into two parts, which
differ greatly in importance in different cases, and of which one or the
other may often be omitted. (1) The determination of th