increases its dilatability, which at low temperatures is inconveniently small.

Neither should each observer neglect to determine for himself the heat stopped by each of his glasses. This may be done also by alternating quadruplet observations made with the glass on and off, beginning and ending with the glass off, and (as in all cases) beginning and ending each quadruplet with a sun observation. For the purpose now in question a very calm day must be chosen, and a great many quadruplets must be taken in succession.

The actinometer is well calculated for measuring the defalcation of heat during any considerable eclipse of the

sun.

The observations should commence an hour at least before the eclipse begins, and be continued an hour beyond its termination, and the series should be uninterrupted, leaving to others the task of watching the phases of the eclipse. The atmospheric circumstances should be most carefully noted during the whole series.

Thermometers for Terrestrial Radiation.-The measure of terrestrial radiation is of no less importance to the science of meteorology than that of solar radiation, but no perfect instrument has yet been contrived for its determination. Valuable information, however, may be derived from the daily register of the minimum nocturnal temperature of a register spirit-thermometer, the bulb of which is placed in the focus of a concave metallic mirror, turned towards the clear aspect of the sky, and screened from currents. Such a thermometer may be read off and registered at the regular hours by day as well as by night, but it must be screened from sunshine, and a thermometer beside it also read off at the same times.

Registers.

To keep a meteorological register with due regularity, a skeleton form (No. 1) should be prepared, by ruling broad sheets of paper into columns destined for the reception of the daily and hourly entries in their uncorrected state, as

read off or otherwise noted. This form may be most advantageously arranged in groups of columns, with general heading (A, B, C, &c.), and particular sub-headings (a, b, c, &c.), so as to class the entries in an order favourable to subsequent comparison and reduction. Thus the group A Α should carry the general heading Date; B, Pressure; C, Temperature of air; D, Moisture; E, Radiation; F, Temperature of water; G, Wind; H, Cloud; 1, Weather; K, Rain; L, Reference; and opposite to every page ruled for entries should stand a blank page for remarks.

Under the general heading A, the sub-heading Aa will indicate the day of the month (marking the Sundays with S, and the days of new, full, and quarters of the moon with their appropriate marks ●, D, O, (); and Ab will contain the hours of observation in each day, following the civil reckoning of time.

B will contain two sub-headings, Ba, Bb, corresponding to columns in which are entered respectively the readings of the barometer and its attached thermometer.

C will contain three: viz. Ca for entries of the external thermometer; Cb, the daily maxima; and Cc, the daily minima placed opposite to the hours at which they are read off on the self-registering thermometer.

D will have two, Da and Db: viz. the readings of the dry and wet bulbs of the hygrometer.

Under E will stand three sub-columns, Ea for solar, and Eb, Ec, for terrestrial radiation. Ea will contain the readings of the black-bulb thermometer exposed in the exhausted tube to the sun at such of the regular hours when it can be observed; Eb, those of the thermometer exposed to clear sky in the metallic reflector; and Ec, those of a similar thermometer placed close beside it, and in all other respects similarly exposed. In these columns may also be entered the observed maxima of these elements, whether obtained by watching the instruments or by self-registering ones: and these observations should be distinguished from the others by enclosing them in parentheses, or by underlining them, &c.

L

F will contain the temperature of the surface-water under the first sub-heading, Fa; and under the second, Fb, that at two fathoms depth: the latter not being taken more than once a day, except when Fa indicates some sudden change.

G will contain the direction of the wind per vane and compass, in its first column, Ga; and its force, as read off on the anemometer, in Gb. If there be an upper and under current of wind, both their directions should be set down above and below a line, like a fraction.

H should have three sub-columns: viz. Ha for the amount of cloud in the region from the zenith down to 30° of altitude, and Hb for the amount below that altitude, each estimated in eighth parts of the whole respective areas of sky included in the two regions (which are equal), according to the best of the observer's judgment. He will contain the prevalent character of cloud, according to the nomenclature of Howard; denoting by C cirrus, by K cumulus,* by S stratus, and by N nimbus, by double letters their combination in transition from one to the other form (as C'S cirro-stratus), and by letters with interposed commas (thus, K, S) the prevalence of one species of cloud in one and another in the other region. Two layers of cloud, one above the other, may be denoted by placing their characteristic letters above and below a line in the manner of a fraction. These forms of cloud are thus characterized :— Cirrus expresses a cloud resembling a lock of hair, or a feather, consisting of streaks, wisps, and fibres, vulgarly known as mares' tails. Cumulus denotes a cloud in dense convex heaps or rounded forms, definitely terminated above, indicating saturation in the upper clear region of the air, and a rising supply of vapour from below. Stratus is an extended continuous level sheet, which must not be confounded with the flat base of the cumulus, where it simply reposes on the vapour plane. The cumulo-stratus, or anvil-shaped cloud, is said to forerun heavy gales of wind.

*To avoid the otherwise inevitable confusion of C and c in MS.

Peculiar aspects of cloud, preceding gales, squalls, or hurricanes, should be specially described in the sheet of remarks or in a journal. Nimbus is a dense cloud spreading out into a crown of cirrus above, and passing beneath into a shower.

Under the heading I will stand a note of the general state of the weather, according to Admiral Beaufort's system of abbreviations, which is as follows:-Numbers from 1 to 12 denote the force of the wind: thus 0 denotes calm ; 1, light air, just perceptible; 2, light breeze, in which a ship, clean full, in smooth water, would go from one to two knots; 3, gentle breeze (from two to four knots); 4, moderate breeze (from four to six knots); 5, fresh breeze, in which a ship could just carry on a wind royals, &c.; 6, stormy breeze (single-reefed topsails and topgallant-sails); 7, moderate gale (double-reefed, &c.); 8, fresh gale (triple-reefed and courses); 9, stormy gale (close-reefed, &c.); 10, whole gale (close-reefed maintopsail and reefed foresail); 11, storm (storm-staysails); 12, hurricane (no canvas can stand). These numbers, in the absence of an anemometer, may be entered in column Gb. The following abbreviations denote the state of the weather:

b. Blue sky, be the atmosphere o. Overcast. The whole sky co

o under any letter denotes a great degree.

K contains only a column, Ka, for the quantity of rain, melted snow or hail, collected in the rain-gauge at the regular hour. One entry a day will suffice, except in rains of unusual heaviness or in paroxysmal discharges, which

will require special note. There will always be room in this column to note the temperature of the falling rain, if remarkable.

Finally, L is a small column at the edge of the page, containing merely numbers of reference, from 1 to the number of lines of entry in the page, to connect each entry with the remarks on it, or on any phenomenon which may have occurred in the interval since the last entry, which it will be probably necessary to enter on another sheet or interleaved page (carrying at its left-hand edge a similar reference column), or with any more extended notes which may form part of a diary such as every observant traveller or voyager ought to keep, and of which a summary for the month, so far as relates to meteorological subjects, should be appended to each monthly register.

Another skeleton form, No. II., should be prepared and ruled in corresponding columns, to receive the corrected and reduced results of the raw observations in Form I. This should have the column A, as in Form I.; B will consist of a single column, viz. the barometer, reduced to 32; C, of the same number as in Form I., containing the corrected thermometer readings; under D will come two columns, Da and Db, of which the former will contain the corrected difference of the dry and wet bulb readings, and the latter the value of F, the elastic force of vapour at the dewpoint by the formulæ already given. E and F will merely contain the corrected values of the corresponding entries in Form I.; and if there be anything in the remaining columns requiring correction or reduction, it will here, of course, be done; if not, those columns must be either carefully copied or simply referred to. In this form should be entered, when needed, the monthly means of the several columns (in calculating which care should be taken to verify the results by repetition); and it is recommended, before adding up the columns, to look down each to see that no obvious error of entry (as of an inch in the barometer, a very common error) may remain to vitiate the mean result. The precaution should also be taken of counting the entries in each column,