The Hurricane Guide | Page 7

instance,
previous to sailing, it should be re-compared with the standard on shore
by the intervention of a portable barometer, and no opportunity should
be lost of comparing it on the voyage by means of such an intermediate
instrument with the standard barometers at St. Helena, the Cape of

Good Hope, Bombay, Madras, Paramatta, Van Diemen's Island, and
with any other instruments likely to be referred to as standards, or
employed in research elsewhere. Any vessel having a portable
barometer on board, the zero of which has been well determined, would
do well, on touching at any of the ports above named, to take
comparative readings with the standards at those ports, and record the
differences between the standard, the portable, and the ship barometers.
By such means the zero of one standard may be transported over the
whole world, and those of others compared with it ascertained. To do
so, however, with perfect effect, will require that the utmost care
should be taken of the portable barometer; it should be guarded as
much as possible from all accident, and should be kept safely in the
"portable" state when not immediately used for comparison. To
transport a well-authenticated zero from place to place is by no means a
point of trifling importance. Neither should it be executed hurriedly nor
negligently. Some of the greatest questions in meteorology depend on
its due execution, and the objects for which these instructions have
been prepared will be greatly advanced by the zero points of all
barometers being referred to one common standard. Upon the arrival of
the vessel in England, at the termination of the voyage, the ship's
barometer should be again compared with the same standard with
which it was compared previous to sailing; and should any difference
be found, it should be most carefully recorded.
The correction for the height of the cistern above or below the
water-line is additive in the former case, subtractive in the latter. Its
amount may be taken, nearly enough, by allowing 0·001 in. of the
barometer for each foot of difference of level.
An example of the application of these several corrections is
subjoined:--
| Attached Therm. 54°·3. |Data for the correction of | | | the Instrument.
| +---------------------------------------+-------------------------------+
|Barometer reading. 29·409 |Neutral point 30·123 | |Corr. for capacity
- ·017 |Capacity 1/42 | | |Capillary action + ·032 |
+---------------------------------------| | | 29·392 |Zero to Royal Society

+ ·036 | |Corr. for capillarity + ·032 |Corr. for altitude above | | |
water-line + ·004 | +---------------------------------------| | | 29·424 | | |Corr.
for temperature - ·068 | | +---------------------------------------| | | 29·356 | |
|Corr. for zero and water-line + ·040 | |
+---------------------------------------| | |Aggregate = pressure at | | |
sea-level 29·396 | |
+---------------------------------------+-------------------------------+
It would greatly facilitate the comparison of the barometric
observations by projecting them in curves when all the proper
corrections have been applied. This may be accomplished by a much
smaller expenditure of time than may at first be supposed. A paper of
engraved squares on which the observations of twelve days may be laid
down on double the natural scale, would be very suitable for the
purpose.[4] The projection of each day's observations would occupy
but a short time; and should circumstances on any occasion prevent the
execution of it, when the ship was becalmed or leisure otherwise
afforded, it would form an interesting and useful occupation, and serve
to beguile some of the tedium often experienced at such intervals.
Registers.--For the particular object in view the register need not be
very extensive. One kept in the annexed form will be amply sufficient.
It should, however, be borne in mind that none but uncorrected
observations should find admission; in point of fact it should be strictly
a register of phænomena as observed, and on no account whatever
should any entry be made from recollection, or any attempt made to fill
up a blank by the apparent course of the numbers before and after. The
headings of the columns will, it is hoped, be sufficiently explicit. It is
desirable in practice that the column for remarks should embrace an
entire page opposite the other entries, in order that occasional
observations, as well as several other circumstances continually coming
under review in the course of keeping a journal, may find entry.
METEOROLOGICAL REGISTER kept on board _____ during her
voyage from ____ to ____ by ____.
+---------+----+------+-------+------+------------------+--------+----------+
| | | | | | Wind. | | | | | | | | Att. |-----------+------| | | | Date. |Lat.| Long.|

Barom.| Ther.| Direction.|Force.| Remarks| Observer.|
|---------|----|------|-------|------|-----------|------|--------|----------| | |h. m.|
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |