they threw out a parcel of books, which made the balloon ascend, when they were about midway between France and England.

At a quarter past two, finding themselves again descending, they threw away the remainder of their books, and in ten minutes after, they had a most enchanting view of the French coast. Still, however, the balloon descended; and as they had now no more ballast, they were obliged to throw away their provisions, the wings of their boat, and every

thing they could possibly spare. "We threw away (says Dr. Jefferies) our only bottle, which, in its descent, cast out a steam like smoke, with a rushing noise; and when it struck the water, we heard and felt the shock very perceptibly on our car and balloon." All this proving insufficient to stop the descent of the balloon, they next threw out their anchors and cords, and at last stripped off their clothes, fastening themselves to certain slings, and intending to cut off the boat as their last resource.

They had now the satisfaction, however, to find that they were fast rising; and as they passed over the highlands of Cape Blanc and Calais, the machine rose very fast, and carried them to a greater height than they had been at any former part of their voyage. They descended safely among some trees in the forest of Guiennes, where there was just opening enough to admit them.

Aerial Voyage of Messrs. Sadler and Livingstone, in 1819.

411. This voyage which was undertaken from Liverpool, is the longest that has ever been made in Great Britain. The balloon ascended at a quarter past two o'clock, and alighted at five minutes past five, at the distance of about a mile and a half from the town of Stockton.

In a space of two hours and fifty minutes, therefore, they traversed a distance of nearly one hundred and ten miles in a lineal direction; and if the undulations and aberrations of the machine are allowed for, it would make at least one hundred and seventy miles. In the course of this voyage, they traversed some of the finest parts of the counties of York and Durham, the views of which both gentlemen describe as sublime and enchanting beyond all description. At the height of nearly two miles from the earth, they took their refreshment,

and drank the health of their sovereign, and prosperity to the town and trade of Liverpool. On approaching a town or village, they frequently descended so low as to be able to converse with the people. They did not suffer much from cold; the mercury in the thermometer generally ranging about 38. Unfortunately, they had no barometer with them; but Mr. Livingstone conjectures, that their utmost elevation might be about four miles and a quarter. Near the town of Stockton, they approached a range of hills; and on surmounting these, were somewhat startled at perceiving themselves within a few miles of the sea. They immediately drew the valve, and alighted with all possible expedition. The intrepid aeronauts undertook this long voyage with the view of trying the power of the balloon, and its capability of crossing the Irish Channel.

412. The Method of filling Air Balloons with Hydrogen Gas.

A A, are two tubs, three feet diameter and two feet deep, inverted in larger tubs; at the bottom of each of the inverted tubs there is a hole, to which is adapted a tin tube E, seven inches diameter, and eight inches long. To these tubes the silken tubes of the balloon are tied. Each of the tubs, B, is surrounded by several strong casks, so regulated in number

and capacity, as to be less than half full when the materials are distributed. In the top of each of these casks are two holes ; and to one of the holes is adapted a tin tube formed so as to pass over the edge of the tub, B, and through the water, and to terminate with its aperture under the inverted tub, A. The other hole, which serves for supplying the cask with materials, is stopped with a wooden plug.

These tin tubes may, however, be 3 inches diameter, and the other holes in proportion.

Two masts with a rope, &c. are used for this machine, although they are not absolutely necessary; because the balloon, by means of a narrow scaffold, or other contrivance, may be elevated five or six feet above the level of the tubs, A A. When the balloon is to be filled, the net is put over it, and suspended as exhibited in C D F ; and having expelled all the common air from it, its silk tubes are fastened round the tin tubes E E, and the materials in the casks are properly proportioned, the iron being first put in, then the water, and lastly, the vitriolic acid. The balloon will soon be inflated by the inflammable air, and support itself without the aid of the rope G H. As the filling advances, the net is adjusted round it; the cords proceeding from the net are fastened to the hoop, N M; the boat, I K, is now suspended from the hoop, M N, and every thing necessary for the voyage is deposited in it. When the balloon is a little more than three quarters full, the silken tubes are separated from the tin tubes, and their extremities being tied, they are placed in the boat. Finally, when the aeronauts are seated in the boat, the lateral ropes are slipped off, and the machine ascends in the air.

In order to produce such a bulk of inflammable air as is necessary for a balloon of thirty feet in diameter, whose capacity is 14,137 cubic feet, there will be required 3,900 lbs. of iron turnings, 3,900 lbs. of vitriolic acid, and 19,500 lbs. of water; with which the balloon will not be above threefourths full.

The Thermometer.

413. This instrument, used for measuring the degrees of heat or cold in any body, consists of a small ball blown at the end with a small glass tube of uniform width throughout. The ball, and part of the tube, are then filled with quicksilver, which has been previously boiled to expel the air. The end of the tube is then hermetically sealed.

The next object is to adapt to this tube a scale which shall indicate with truth the degrees of heat and cold. This is done in the following manner :

It is found by experiment that melting snow and freezing water are always of the same temperature. If, therefore, a thermometer be immersed, in the one or the other, the quicksilver will always stand at the same point. It has been observed, too, that water boils under the same pressure of the atmosphere, and the same temperature.

A thermometer, therefore, immersed in boiling water will uniformly stand at the same point.

Here then are two fixed points, from which a scale may be constructed, by dividing the intermediate space into equal parts, and carrying the same divisions above and below the two fixed points as may be thought necessary.

It is obvious, that all thermometers constructed on this principle may be compared together, for if they have been accurately made, and are placed in the same temperature, they will always point to the same degree on the scale.

200

190

180

1704

100! 250

140

130

The freezing point on this thermometer, which is called Fahrenheit's, is fixed at 32°; the boiling is 212°; the intermediate space (212°-32°) 180° will at one point or other indicate all the degrees of heat between freezing cold and boiling heat; the former where water becomes ice, the latter where water becomes vapour.

The Barometer.

414. The invention and principle of this instrument are due to Torricelli, a pupil of Galileo.

The barometer was first applied to measure the height of mountains, by Pascal the celebrated Geometrician and Divine. For every 103 feet the barometer ascends, the mercury falls of an inch, 103 feet of air being equal to of an inch of mercury on the surface of the earth.

The barometer on the top of Snowdon in Wales, sinks 3.67 inches, therefore that mountain is 3720 feet in perpendicular height.

Barometers are of various kinds, and may be classed under the following heads; viz. the common or straight barometer, the diagonal barometer, the horizontal or rectangular barometer, and the wheel ba

rometer.

A thermometer should always be attached to the barometer, and by the side of it a scale of correction, to show how much to add or subtract, from the height of the mercury, in the barometer, for the degree of temperature; for it is evident, that the mercury in the tube will be affected by heat and cold in the same manner as the thermometer, and, on that account, it will not shew the true weight of the atmosphere.

Besides the barometer, there are other instruments used for meteorological purposes, as the thermometer, hydrometer, wind-gage, rain-gage, electrometer, &c.

To be well enabled to prognosticate the change of weather, accurate observations ought to be made with all these instruments, aided by experience and knowledge of natural philosophy and chemistry; and even then, it requires more science than we are possessed of, to predict with certainty the alterations of the weather.

However, as the barometer is the most useful of these, and as it undoubtedly affords us considerable assistance, we shall lay down such directions as are most approved for this purpose.

1. The rising of the mercury presages, in general, fair weather; and its falling, foul weather; as rain, snow, high winds, and storms.

2. In very hot weather the falling of the mercury foretells thunder.

3. In winter, the rising presages frost; and in frosty weather, if the mercury fall three or four divisions, a thaw will certainly follow. But in a continued frost, if the mercury rise, it will certainly snow.

4. When foul weather happens soon after the falling of the mercury, expect but little of it; and, on the contrary, expect but little fair weather, when it proves fair shortly after the mercury has risen.

5. In foul weather, when the mercury rises much and high, and so continues for two or three days before the foul wea ther is quite over, then expect a continuance of fair weather to follow.

6. In fair weather, when the mercury falls much and low, and thus continues for two or three days before the rain