Marine Barometer Adopted By Her Majesty's Government

On the recommendation of the Kew Observatory Committee of the British

Association for the Advancement of Science.

This instrument should be suspended in a good light for reading, but out

of the reach of sunshine or the heat of a fire or lamp. It should be as

nearly amidships, and exposed as little to sudden changes of

temperature, gusts of wind, or injuries, as possible. In a ship of war

hould be below the lowest battery or gun-deck. Light should have

access to the back of the tube, to admit of setting the index so as to

have its lower edge a tangent to the surface of the mercury--the eye

being on the same level, which is known by the back and front edges of

the index being in one line with the mercury surface. White paper or

card will reflect light for setting the vernier correctly. The height of

the cistern above or below the ship's water-line should be ascertained,

and entered on the register.

It is desirable to place the barometer in such a position as not to be

in danger of a side blow, and also sufficiently far from the deck above

to allow for the spring of the metal arm in cases of sudden movements of

the ship.

If there is risk of the instrument striking anywhere when the vessel is

much inclined, it will be desirable either to put some soft padding on

that place, or to check movement in that direction by a light elastic

cord; in fixing which, attention must be paid to have it acting only

where risk of a blow begins, not interfering otherwise with the free

swing of the instrument: a very light cord attached above, when

possible, will be least likely to interfere injuriously.

The vernier, as usual in standard barometers, reads to the two

thousandth (.002) part of an inch. Every long line cut on the vernier

corresponds to .01 part; each small division on the scale is .05; the

hundredth parts on the vernier being added to the five when its lower

edge is next above one of the short lines; or written down as shown by

the figures on the vernier only, when next above one of the divisions

marking tenths.

In placing this barometer, it is only necessary to fix the instrument

carefully, as indicated in the above directions, and give a few gentle

taps with the fingers on the bottom, to move the mercury. Without

further operation it will usually be ready for observation in less than

an hour.

When moving the barometer, or replacing it in its case, the mercury

should be allowed to run gently up to the top of the tube, by holding

the instrument for a few minutes inclined at an angle. The vernier

should be brought down to the bottom of the scale. No other adjustment

for portability is required. During carriage, it ought to be kept with

the cistern end uppermost, or lying flat, the former position being


If the mercury should not descend at first by a few gentle taps, use

sharper (but of course without violence), by which, and two or three

taps, with the finger ends, on the tube--between the scale and the

tangent screw--the mercury will be made to begin to descend.

In reading off from a barometer, it should hang freely, not inclined by

holding, or even by touch.

Sometimes, though rarely, at sea the mercury seems stopped. If so,

take down the instrument (after sloping), reverse it, tap the tube

gently while the cistern end is upwards, and then replace as before.

* * * * *