used in observations of intensity), and obtain the true inclination from the mean of the angles read in eight different positions of the instrument, following the order of observations described in Appendix No. 2. The difference between the true inclination thus obtained, and the apparent inclinations with the face East and West observed with the needle used at sea, ascertained at the several shore stations, furnish one of the data from which the index correction to be applied to the observations made at sea is to be computed.

4. When Mr. Fox's apparatus is furnished with more than one needle for the observations of intensity, each needle must be successively substituted in the shore observations for the needle used at sea, and the inclination as well as the angles of deflection with constant weights observed with it.

ARTICLE V.

SECOND DIVISION, SECTION 2.

METEOROLOG Y.

BY SIR J. F. W. HERSCHEL, BART.

THERE is no branch of physical science which can be advanced more materially by observations made during sea voyages than meteorology, and that for several distinct reasons. 1st. That the number and variety of the disturbing influences at sea are much less than on land, by reason of the uniform level and homogeneous nature of its surface. 2ndly. Because, owing to the penetrability of water by radiant heat, and the perpetual agitation and intermixture of its superficial strata, its changes of temperature are neither so extensive nor so sudden as those of the land. 3rdly. Because the area of the sea so far exceeds that of the land, and is so infinitely more accessible in every part, that a much wider field of observation is laid open, calculated thereby to afford a far more extensive basis for the deduction of general conclusions. 4thly. The sea being the origin from which all land waters are derived, in studying the hygrometrical conditions of the sea atmosphere we approach the chief problems of hygrology in their least involved and complicated form, unmixed with those considerations which the perpetually varying state of the land (as the recipient at uncertain intervals of derivative moisture) forces on the notice of the meteorologist of the continents. Nor ought it to be left out of considera

tion that this, of all branches of physical knowledge, being that on which the success of voyages and the safety of voyagers are most immediately and unceasingly dependent, a personal interest of the most direct kind is infused into its pursuit at sea, greatly tending to relieve the irksomeness. of continued observations, to insure precision in their registry, and to make their partial or complete reduction during the voyage an agreeable, as it always is a desirable object.

It happens fortunately that almost every datum which the scientific meteorologist can require is furnished in its best and most available state by that definite, systematic process known as the "keeping a meteorological register," which consists in noting at stated hours of every day the readings of all the meteorological instruments at command, as well as all such facts or indications of wind and weather as are. susceptible of being definitely described and estimated without instrumental aid. Occasional observations apply to occasional and remarkable phenomena, and are by no means to be neglected; but it is to the regular meteorological register, steadily and perseveringly kept throughout the whole of every voyage, that we must look for the development of the great laws of this science.

The following general rules and precautions are necessary to be observed in keeping such a register:

1. Interruptions in the continuity of observations by changes of the instruments themselves, or of their adjustments, places, exposure, mode of fixing, reading, and registering, &c., are exceedingly objectionable, and ought to be sedulously avoided. Whenever an alteration in any of these particulars is indispensably necessary, it should be done as a thing of moment, with all deliberation, scrupulously noted in the register, and the exact amount of change thence arising in the reading of the instrument (whether by alteration in its zero point, or otherwise). ascertained.

2. As far as possible, registers should be complete: but if, from unavoidable causes, blanks occur, no attempt to fill

them up subsequently from general recollection, or (which is worse, and amounts to a falsification) from the apparent course of the numbers before and after, should ever be made. The entries in the register made at the time of observation should involve no reduction or correction of any kind, but should state the simple readings off of the several instruments, and other particulars just as observed. This does not of course prevent that blank columns left for reduced and corrected observations should be filled up at any convenient time. On the contrary, it is very desirable that such should be the case-the sooner after the observation, consistently with due deliberation, the better, on every account, unless some datum be involved requiring subsequent discussion for its determination.

3. The observations of each kind should, if possible, all be made by one person; but as this is often impracticable, the deputy should be carefully instructed by his principal to observe in the same manner, and the latter should satisfy himself, by comparative trials, that they observe alike.

4. If copies be taken of registers, they should be carefully compared with the originals by two persons-one reading aloud from the original, and the other attending to the copy, and then exchanging parts-a process always advisable when great masses of figures are required to be correctly copied.

5. The registers should be regarded (if kept in pursuance of orders, or under official recommendation) as official documents, and dealt with accordingly. If otherwise, a verified copy, or the original (the latter being preferred), signed by the observer, should be transmitted to some public body interested in the progress of meteorological science, through some official channel, and under address "To the Secretary of, &c. &c." Circuitous transmission hazards loss or neglect, and entails expense on parties not interested.

6. The register of every instrument should be kept in parts of its own scale as read off; no reduction of foreign measures or degrees to British being made. But it should

of course be stated what scale is used in each. British observers, however, will do well to use instruments graduated according to British units.

7. The regular meteorological hours are 3 A.M., 9 A.M., 3 P.M., and 9 P.M., mean time at the place. Irksome as it may be to landsmen to observe at 3 A.M., the habits of life on shipboard render it much less difficult to secure this hour in a trustworthy manner; and the value of a register in which it is deficient is so utterly crippled, that, whatever care be bestowed on the other hours, it must on that account hold a secondary rank. The hours above, it must be borne in mind, are the fewest which any meteorological register pretending to completeness can embrace. By any one, however, desirous of paying such particular attention to this branch of science as to entitle him to the name of a meteorologist, a three-hourly register-viz. for the hours 3, 6, 9, A.M., noon; 3, 6, 9, P.M., midnight-ought to be kept; and in voyages of discovery, where scientific observation is a prominent feature, the register ought to be enlarged, so as to take in every odd hour of the twentyfour; thus including, without interpolation, the six-hourly or standard series. Any series of hours which does not divide the twenty-four hours equally (i. e. into intervals equal to each other), is, in the present state of meteorological computation and knowledge, comparatively worthless.

8. Hourly observations should be made throughout the twenty-four hours on the 21st of each month (except when that day falls on a Sunday, and then on the Monday following), commencing with 6 A.M., and ending at 6 A.м. on the subsequent day, so as to make a series of twenty-five observations. At all events, if this cannot be done monthly, it ought not to be omitted in March, June, September, and December. These are called "term observations." If any remarkable progressive rise or fall of the barometer be observed to pervade this series, it will be well to continue it until the maximum or minimum is clearly attained, with a view to comparison with other similar series elsewhere obtained, and thus to mark the progress of the aërial wave