point, the bulbs and a considerable
portion of the tubes of the thermometers, are immersed in pounded ice.
For the higher temperatures, the thermometers are placed in a
cylindrical glass vessel containing water of the required heat; and the
scales of the thermometers intended to be tested, together with the
Standard with which they are to be compared, are read through the glass.
In this way the scale readings maybe tested at any required degree of
temperature, and the usual practice is to test them at every ten degrees
from 32 deg. to 92 deg. of Fahrenheit. For this range of 60 deg. the makers who
supply Government are limited to 0.6 of a degree as a maximum error of
scale reading; but so accurately are these thermometers made, that it
has not been found necessary to reject more than a very few of them.

* * * * *

Hydrometers are tested by careful immersion in pure distilled water; of
which the specific gravity is taken as unity.

In water less pure, more salt, dense, and buoyant, the instrument floats
higher, carrying more of the graduated scale out of the fluid.

The zero of the scale should be level with the surface of distilled
water, and rise above it in proportion as increase of density causes
less displacement.

The scale is graduated to thousandths--as far as .040 only--because the
sea water usually ranges between 1.014 and about 1.036. Only the last
two figures need be marked.

LONDON:
Printed by GEORGE E. EYRE and WILLIAM SPOTTISWOODE,
Printers to the Queen's most Excellent Majesty.
For Her Majesty's Stationery Office.

FOOTNOTES:

[1] In South latitude the South wind corresponds to our North wind in
its nature and effects. The Easterly and Westerly winds retain their
respective peculiarities in both hemispheres.

[2] Exclusive of local land and sea breezes of hot climates.

[3] Glass, barometer, column, mercury, quicksilver, or hand.

[4] Or atmosphere, or the atmospheric fluid which we breathe.

[5] Or exhaustion.

[6] A vacuum.

[7] See pages 24 and 25.

[8] Thirty-two degrees is the point at which water begins to freeze, or
ice to thaw.

[9] Evaporation.

[10] The two thus combined making a hygrometer: for which some kinds of
hair, grass, or seaweed may be a make-shift.

[11] It stands lower, about a tenth of an inch for each hundred feet of
height directly upwards, or vertically, above the sea; where it