additional recommendation of easily accounting for certain other singular phenomena.

It is known from balloon ascents that, in general, the atmosphere is arranged in horizontal strata of considerable depth or thickness, alternately moist and dry,-temperature diminishing steadily with increase of height in the moist, and remaining nearly constant throughout the dry, strata. These strata have usually horizontal velocities, differing (sometimes considerably) both in magnitude and direction. Thus near the common boundary of two such strata, fluid friction will in general tend to produce vortex motion, the vortex columns being at first nearly horizontal, with their ends at the boundary, which is a surface of discontinuity.

A complete investigation of the possible circumstances would show four quite different cases:—

moist

} air, with its ends turning {down}

dry

The half vortex-ring thus formed tends, so far as it can, to become semicircular. It may thus extend downwards to the earth or upwards into the higher regions of the atmosphere.

If it extend downwards nearly to the earth, the lower portion will soon be destroyed by friction, and we shall have a couple of vertical vortex columns, with their ends respectively in the surface of discontinuity, and on the ground. They will of course rotate in opposite directions about the vertical, and their mutual influence will tend to cause them to progress in directions parallel to one another, the motion of each being in the same direction as that of the rotatory motion of the side which it at the moment turns to the other. This is exactly the presumed case of the little storms in the Tay and Forth valleys above referred to; the south side of the Tay column (that turned towards the Forth), moving eastward about the axis, while the axis itself moves to the east.

This theory is evidently capable of at once explaining the apparently sudden occurrence of such storms (of which waterspouts must be looked upon as small but quickly rotating examples), when the lower atmosphere has for hours been in a dead calm.

The disturbance has, in fact, its origin above the lower stratum, and works its way downwards into it.

It is also competent to explain the production of similar rotating storms in the higher regions of the atmosphere-many miles above the earth's surface-and thus to account for that by no means small number of cases of so-called "summer-lightning," which obviously cannot be explained by the occurrence of an ordinary thunderstorm at such a distance as to be below the spectator's horizon.

I have already explained to the Society that a possible source of at least a large part of the electric charge of a thunder-cloud is the contact-electricity of water-vapour and air. Thus while the precipitation of the vapour develops heat, the water particles precipitated are strongly electrified. And the aggregation into one of a number of equal little drops all charged to the same potential may increase the potential in any ratio whatever. Thus the charge on each drop in a large cloud may become so great that the electricity is driven entirely to the particles at its surface. This is supplementary to, and does not interfere with, Sir W. Thomson's explanation of the process by which the vapour is condensed.

It is possible that taking place in greatly larger spaces of air, but to a much smaller extent in each cubic foot, this sudden production, and as sudden scattering in all directions, of considerable quantities of electricity, may account for some of the main phenomena of the Aurora.

3. An Application of Professor James Thomson's Integrator to harmonic Analyses of Meteorological, Tidal, and other Phenomena, and to the Integration of Differential Equations. By Sir W. Thomson.

A first rough Model of Professor J. Thomson's Integrator was shown.

4. Note on the Thermo-Electric Position of Cobalt. By Professor Tait.

5. On a Glass Digester in which to Heat Substances under Pressure. By Dr E. A. Letts.

The objections to the use of sealed tubes are known to every practical chemist, and are a serious drawback to their employment. The chief of these are the time expended in the manufacture of the tubes, the amount of skill in glass-blowing required, the danger experienced in opening them, and above all, the fact that only a small quantity of material can be heated at one operation. Moreover, the same tube can seldom be used for more than three or four experiments, as each time it is sealed up its neck must be drawn out, and its length thus considerably decreased. These disadvantages were especially felt by me whilst preparing bromacetic acid, which was required in considerable quantities, and where as many as half a dozen tubes of bromine and acetic acid had to be heated before 100 grammes of the acid could be obtained. To obviate these objections I have had an apparatus constructed, which consists of a cylinder of glass, the walls of which are about half an inch thick. Its length is fifteen inches, its external diameter three inches, and its capacity about 600 cubic centimetres. At one end it is drawn out to a tube, whose aperture is only about one-sixth of an inch in diameter, though its walls are as thick as the rest of the apparatus. Originally this tube was provided with a stopcock, but at Professor Brown's suggestion, I have substituted a glass plate, which is ground fiat, and accurately adapted to the top of the tube.

In order to keep the glass plate pressing on the tube the whole apparatus is placed in a frame, consisting of three brass wires arranged symmetrically around the cylinder, and attached by means of nuts, below, to a brass ring, and above, to a brass plate, through which latter a screw passes, which, when turned, presses on a brass plate placed on the glass cap.

As any experiments with such an apparatus would be attended

with danger, were it necessary to be in its neighbourhood, it occurred to me that an automatic arrangement might be employed to give notice that the temperature had been reached to which it was intended to subject the digester.

For this purpose I employed a thermometer with a somewhat wide tube and large bulb. A platinum wire is sealed into the bulb, and touches the mercury, whilst a brass wire passes down the tube, and is held in position by a binding screw. The two wires are connected with an electric bell, the brass wire being so adjusted, that when a particular temperature is reached the mercury touches its end, and thus completes the circuit, and causes the bell to ring.

In order to test the digester, about 200 grammes of a mix. ture of two-parts bromine and three of acetic acid was placed in it, and after fixing it in its frame, the whole apparatus was immersed in an oil bath and heated to 150° C., the temperature at which reaction in this case takes place. The experiment was made in a cellar, and the bell placed in a room some distance off. The gas to heat the oil bath was led by a tube from another cellar, so that it could be regulated without going near the digester. In about an hour and a half the bell rung, and thereupon the gas was shut off; and on examining the digester next day, it was found that the reaction had taken place, and that only twelve grammes of product had been lost-a very inconsiderable quantity.

As the action of bromine on acetic acid is very sudden, and accompanied by the disengagement of a large volume of hydrobromic acid, the apparatus may be considered to have undergone a very severe test, and that its efficacy for all ordinary purposes is

established.

Should the digester come into general use, it will certainly save chemists much time and labour.

The following Gentlemen were elected Fellows of the Society:

Rev. FRANCIS LE GRIX WHITE, M.A.

JAMES DUNCAN, Esq., Benmore.

Rev. NORMAN MACLEOD.

J. S. FLEMING, Esq.

JAMES DOUGLAS H. DICKSON, M.A. Glasg., B.A. Camb.

Monday, 20th March 1876.

SIR WILLIAM THOMSON, President, in the Chair.

The following Communications were read:

1. On the Connection between Cohesion, Elasticity, Dilatation, and Temperature. By Professor George Forbes.

(Abstract.)

At various times there have arisen supporters of one or other of two extreme hypothesis concerning the nature of what we define as force. These are the hypothesis of "action at a distance" and of "no action at a distance."

According to the latter hypothesis, the centre of gravity of no hody, however large or however small, can be moved from a position of rest, nor can its motion be altered in direction or amount, except by direct collision with another portion of matter.

Starting from this supposition as a basis of argument, and without assuming anything further as to the manner in which the different physical forces are caused by collisions, it is possible to arrive at some very general theorems; and from these theorems conclusions may be drawn as the nature and connection of some of the physical forces, which are necessarily true if the hypothesis of no action at a distance be true.

The principal result of these theorems is the following:-Let a rod be chosen of any substance whose cohesion and elasticity do not vary enormously with the temperature. Let a be its expansion, in terms of its length, when the temperature is raised 1°. Let ẞ be the compression of the same rod, in terms of its length, when a unit weight is supported at its summit. Let c be the number of these units which, when suspended by the rod, suffice to break it by sudden rupture. Let be the absolute temperature at which all these experiments are made. Then the theory leads us to the conclusion that

Only a few experiments have been made by which we can test