17. Instructions for the Sea-coast Barometer.—The directions for fixing the barometer, and making it portable when it has to be removed, should be attended to carefully. The barometer should be suspended against a frame or piece of wood, so that light may be seen through the tube. Otherwise a piece of paper, or a white place, should be behind the upper or scale part of the tube.

When suspended on a hook, or stout nail, apply the milled-head key (which will be found just below the scales) to the square brass pin at the lower end of the instrument, and turn gently toward the left hand till the screw stops; then take off the key and replace it for use, near the scale, as it was before. The cistern bottom being thus let down, the mercury will sink to its proper level quickly.

In removing this barometer it is necessary to slope it gradually, till the mercury is at the top of the tube, and then, with the instrument reversed, to screw up the cistern bottom, or bag, by the key, used gently, till it stops. It will then be portable, and may be carried with the cistern end upwards, or lying flat; but it must not be jarred, or receive a concussion.

18. French Sea-coast Barometer.—The French have imitated this form of barometer for coast service, and have translated Admiral FitzRoy’s indications for the scale as follows:—

LA LA
HAUSSE BAISSE
INDIQUE. INDIQUE.
——— ———
des Vents de la des Vents de la
PARTIE DU PARTIE DU
N.E. S.O.
(du N.O. á l’E) (du S.E. á l’O.)
par le NORD. par le SUD.
DE LA DE
SÉCHERESSE. L’HUMIDITÉ.
——— ———
un VENT un VENT
PLUS FAIBLE PLUS FORT
EXCEPTÉ S’IL PLEUT EXCEPTÉ S’IL PLEUT
AVEC DE FORTES BRISES AVEC DE PETITES BRISES
du N.E. du N.E.
——— ———
Mouvements lents,
Temps durable.
———
Mouvements rapides,
Temps variable.		 Le commencement
de la hausse,
après une grande
baisse présage
un Vent violent.

Fig. 13.

Fig. 14.

MARINE BAROMETERS.