veller has no stop watch, the better way would be to apply the watch to his ear, and count its beating, of which 5 usually go to a second; in this case the dividend will be 150 instead of 30, and the diviser the number of beats observed.

OMBROMETER, OR RAIN-GUAGE.

The simplest form of the rain-guage, that recommended by the Committee of the Royal Society, is still a cumbersome object for a traveller to take with him; if, however, he be stationary, and get the instrument constructed, he should do so. 66 'It consists of a tin or zinc box, exactly ten inches by the side, open above, and receiving at an inch below its edge a funnel, sloping to a small hole in the centre. On one of the lateral edges of the box, close to the top of the cavity, is soldered a short pipe in which a cork is fitted. The whole should be well painted. The water which enters this guage is poured through the short tube into a cylindrical glass vessel, graduated to cubic inches and fifths of cubic inches. Hence one inch depth of rain in the guage will be measured by a hundred inches of the graduated vessel, and 1-1000th inch of rain may be very easily read off."

It is very much to be desired that more than one of these guages should be erected, or at least one placed with its edge nearly level with the ground, and another upon the top of the highest building, rock, or tree in the immediate vicinity of the place of observation, the height of which must be carefully determined; it having been satisfactorily ascertained that the height of the guage above the ground is a very material element in the quantity of rain which enters it. The quantity of water should be daily measured and registered at 9 A.M."*

This daily registering at 9 A.M. applies of course to stationary observations only, and even then is useless unless rain has fallen. In general, travellers will set up their rainguages and observe with them, when and where they can.

To the instrument just described we would add, a thermometer for taking, at the time of a shower, the temperature of the rain. This thermometer should have a flattened bulb and a bent tube, and so fitted into the funnel of the

* See "Report of the Committee of Physics and Meteorology."

guage that its whole scale be above the surface, while the flattened bulb be exactly under the hole of the funnel, so that the rain-water may fall directly on its flat surface and communicate its temperature to the instrument.

ATMOMETER FOR ESTIMATING THE EXTENT OF
EVAPORATION.

Leslie very justly says, that observations on evaporation are as interesting as those on the fall of rain. Unfortunately, however, evaporation is modified by so many causes, that precise observations of its amount are by no means easy. The atmometer described by Leslie is perhaps the most correct; but it is an instrument which can hardly form part of a traveller's baggage. The progress of evaporation therefore must be deduced from the observed indications of the dew point or of the wet bulb hygrometer. Stationary observers, however, should not fail to make regular observations with the atmometer, and such travellers as can transport one, will be doing much service to science by using it frequently. The instrument consists of a porous earthenware ball, with a long attached graduated glass tube; it may be had of any of the principal philosophical instrument makers.

ANEMOMETER, or wind-gUAGE.

Of the different instruments that have been constructed for ascertaining the force of the wind, that of Mr. Osler, of Birmingham, is perhaps the most complete; for, by its adjustments, it registers for itself, and furnishes, without trouble, all the requisite data of force, direction, duration, &c.; but the apparatus is bulky and fit only for setting up at fixed observatories. Of portable instruments, such as a traveller may easily carry with him, the best is that known as LIND'S WIND-GUAGE. It consists of a glass tube bent into the form of an inverted siphon, the branches being close and parallel. It is open at both ends, at one of which a metallic cylinder, of equal bore with the tube, is fixed, bending at right angles to the tube. The instrument is set upright and turns on a pivot; to the top of it, a small vane is attached, so that the open metal orifice is always presented to the wind. The tube is graduated and filled

with water to 0° of the scale. Sometimes both the tubes are graduated, in which case, the amount of the depression of the fluid in one branch of the guage, and of its ascension in the other, being added, gives the force of the wind. If only one of the branches be graduated, then twice the amount of the ascent or descent from 0 of the scale is the height of the column of water supported.

The length of the column being observed, the following table (extracted from the Report of the Committee of Physics of the Royal Society) will give the force of the wind on every square foot of a body opposed to its direct action:—

In great degrees of cold, a saturated solution of sea-salt may be used instead of water, the specific gravity of which is 1.244. If the force in the above Table, for any height, be multiplied by the specific gravity, the product will be the true force, as measured by the solution.

If an index be added to the instrument, and the disc on which it stands be divided like a compass card, then, by setting the instrument with the North and South points of the card in the direction of the meridian (true); or if magnectic to be so specified, the direction, as well as the force of the wind, will be indicated.

DROSOMETER.

This is an instrument for measuring the quantity of dew. We recommended for this purpose a metal funnel, of five inches in diameter, sloping at an angle of 30°, and terminating in a small hole and very short pipe. This funnel must screw into the neck of a glass tube of equal bore, and a quarter of an inch in diameter. This tube must be graduated, so that each degree may indicate the thousandth part of an inch on the external aperture. The bottom of the tube must screw into a solid foot, so that the instrument may stand firm. To observe with this instrument, see OPERATIONS.

ELECTROMETER.

There are few meteorological data more interesting than those respecting the electrical state of the atmosphere; but, unfortunately, this is a subject not yet fully understood. The electricity of the air is observed by means of electrometers or electroscopes, of which there are several of various constructions, as De Saussure's, Volta's, Singer's, Bohnenberger's, &c. Leslie prefers Singer's, but Bohnenberger's has the advantage of indicating the kind of electricity communicated to the conductor.

Whichever of these instruments is used, and the choice may be left to the option of individuals, it must be connected by a fine copper wire with a conductor, which as the report of the Committee of Physics of the Royal Society observes, may be any temporary contrivance as "a common fishing rod, having a glass stick well varnished with shell-lac, substituted for its smallest joint; to the end of the glass must be fixed a metallic wire, terminating in a point, and to the end of this point the copper wire must be fixed which connects the conductor with the electroscope.

CYANOMETER.

This is an instrument constructed by De Saussure for measuring the intensity of the blue colour of the sky. It consists of fifty-three slips of paper, about a quarter of an inch broad, and one inch long, stained with the successive

shades of blue, from the lightest to the darkest. These are arranged in a circle, and the colour of the heavens is compared with these, and the corresponding tint determined.

The great defect of this instrument is the difficulty of obtaining comparative instruments; and even the same Cyanometer changes its tints by exposure to air and light. Other cyanometers than that described, have been proposed, but none that we know of are perfect. This is to be regretted, as the intensity of the colour of the sky, varying with the state of the atmosphere, and with the heights at which the observation is made, it becomes interesting to note the tint of the heavens under different circumstances.

PHOTOMETER.

This instrument, though not strictly necessary to the traveller, is so extremely portable, particularly that form of it which is called the portable photometer, that we cannot but recommend to the traveller to have one with him. The object of this little delicate instrument is, to ascertain the relative intensities of light, as depending either on the times of the day, the seasons or the heights of places. Its applications are very various, and it serves to supply some very interesting data of general physics.

INSTRUMENT FOR OBSERVING THE DIRECTION OF THE

UNDULATORY MOTION OF EARTHQUAKES.

For this purpose treacle or other viscous substance has been recommended, which being put into a bason, will, by the marks it leaves after agitation, show the direction of the wave, and in some degree its force; but treacle or other viscous fluid is not always to be had, particularly by the traveller, and moreover, in order to render the observations made at different places comparative, the same substance and of the same specific gravity should be employed. Fortunately water will answer the purpose though not so well as treacle.

We recommend then, a tin or copper bason, hemispherical within, and having its inner surface whitened but not polished; the composition used must be such as water will wet but not dissolve. From a point in the exact centre of the bottom, let black lines be drawn to the number of 32, and at the top let the usual letters and degrees of the compass be marked; in addition to this let black and equidistant horizontal circles be painted on the inner surface of the basin, these may be