placed in a calorimeter, which measure the quantities of heat evolved. We determine, in the first place, the relative quantities of heat evolved in the two coils when neither of them exerts any exterior action. The apparatus is then arranged so that one of the coils may produce exterior work, and we see whether the relative quantities of heat remain the same.

The coils employed were of copper wire covered with silk; they were placed in calorimeters filled with rectified oil of turpentine, a non-conducting liquid, of which the elevation of temperature was determined. The calorimeters first employed were brass vessels, of which the annular form would allow of the introduction into the interior of the coil, of a cylinder of soft iron, or of the body upon which the exterior action was to be exerted. Subsequently glass calorimeters were made use of. The calorimetric methods of M. Regnault were adopted.

In operating with a brass calorimeter and a cylinder of soft iron in the interior of the coil, currents of induction are developed in the walls of the calorimeter itself, which evolve a great quantity of heat; the experiments made in this way consequently present a very considerable source of error, but they demonstrate that the exterior work exerted by the current is very considerable; in fact, the excess of heat betrayed by the calorimeter containing the soft iron, sometimes rises to th of the heat evolved in the coil itself.

With glass calorimeters, after the elimination of numerous causes of error which render these experiments very delicate, a negative result was obtained, that is to say, the relative quantities of heat evolved in the two coils were found not to be modified when one of these coils produced an action exterior to itself by induction. The following are the numerical results of the last experiments which were made:Elevations of temperature of the calorimeter containing the coil which exerted an exterior action.

From this we must conclude that the heat evolved is the same in the two cases, and that it is not in the part of the current which exerts an exterior action that we must seek for the modification which the interior work must undergo under these circumstances.

Description of an Arrangement of Grove's Battery.

By G. JOHNSTONE STONEY, A.M., M.R.I.A.

The earthenware cells in this arrangement were the ordinary flat cells commonly used for Grove's battery, consisting of flat porous cells containing nitric acid, placed within outer cells of glazed earthenware containing acidulated water.

A sheet of platinum foil hangs into each cell of nitric acid, and on either side two parallel plates of zinc stand in the acidulated water of the outer cell. A stout copper wire effects the necessary connexion between the two zinc plates of one element and the platinum of the next. This connecting wire takes a form somewhat resembling that of an S, being first soldered along the top of one zinc plate; then after a semicircular bend brought along the top of the other zinc plate of the same element and soldered to it, and finally, by a second semicircular bend, brought along the top of the platinum of the next element and soldered to it. The same mode of connexion was of course repeated throughout the battery, with the exception of trifling and obvious modifications at the end of each trough of cells. The soldered joints were varnished; each of those which attach the platinum plates was further protected from spatters and fumes by a piece of loose gutta-percha tubing, which was slipped lengthways over the wire after its under side had been slit for the platinum foil to pass through.

The S-shape of the connecting wires admits of any set of metals being at any moment withdrawn or introduced without disturbing the others.

The zincs not being folded at the bottom may be amalgamated by dipping them, first into acidulated water, then into a spare outer cell filled with mercury, and finally into their place in the battery. The excess of mercury drains off, and will be found after the battery has been taken asunder.

In dismounting the battery, the whole series of metals in each trough was withdrawn together by a frame, the essential parts of which are two parallel bars of wood, the interval between which can be adjusted, and which are somewhat longer than the trough. These bars are first to be separated sufficiently to enable the frame to be passed down over the S-connecting wires of the metals. The interval between the bars is then to be reduced, so that on raising the frame all the metals are carried with it, being supported by the projecting semicircular bends of the connecting wires resting on the bars of the frame. Frame and all are to be immediately dipped into a tank of water, and the frame with its metals then laid aside to drain till the battery is again required.

The workmanship of this form of battery is throughout of the simplest description".

On Mr. Whitehouse's Relay and Induction Coils in action on Short Circuit. By Professor W. THOMSON, LL.D., F.R.S.

The peculiarities of Mr. Whitehouse's induction coils, which fit them remarkably for the purpose for which they are adapted, as distinguished from the induction coils by which such brilliant effects of high intensity are obtained, were described. The chief part of the telegraphic receiving apparatus, the relay, was fully described, and was shown in action, through thirty yards of the Atlantic cable, after some remarks explaining the general nature of a relay,—an electrical hair-trigger. The relation of Mr. Whitehouse's relay to the Henley receiving instrument, was pointed out. The author expressed his conviction, that by using Mr. Whitehouse's system of taking advantage of each motion for a single signal, instead of the to-and-fro motion, as in all systems hitherto practised, the Henley single needle instrument might be easily used, so as to give as great a speed on one line of wire alone, as is at present attained by two with the double needle instrument. The beautiful method of reading by bells would be most ready and convenient for giving the indications to be interpreted as the messages, but the author believes that either by the eye or ear, messages may be read off with the rapidity and ease which will render the use of one telegraph wire in all respects as satisfactory as that of two.

On the Effects of Induction in long Submarine Lines of Telegraph.
By Professsor W. THOMSON, LL.D., F.R.S.

A general explanation of the theory was given, and the "law of squares” was proved to be rigorously true. It was pointed out, that when the resistances of the instruments employed to generate and to receive the electric current are considerable in comparison with the resistance of the line, the observed phenomena do not fulfil the law of squares, because the conditions on which that law is founded are deviated from. The application of the theory to the alternate "positive" and "negative" electrical actions used by Mr. Whitehouse for telegraphing was explained, and the circumstances which practically limit the speed of working were pointed out. Curves illustrating the enfeeblement of the current towards the remote end of the telegraph line, and the consequent necessity of the high pressure system introduced by Mr. Whitehouse, were shown. The embarrassment occasioned by the great electrical effect through the wire, which follows the commencement of a series of uniform signals with a full strength of electrical force, was illustrated in one diagram, which showed a succession of eight impulses following one another at equal intervals of time, and giving only one turn of the electrical tide at the remote end, or two motions of the relay, including the initial effect. The remedy suggested by

*For many purposes to which a battery may be applied, it is convenient to be able to form a connexion directly with any required cell. In the battery exhibited to the Association, this was simply provided for by one end of each S-wire being allowed to project and turned up for a binding-screw to be soldered to it.

the author was illustrated by another diagram, in which a succession of seven equal alternate applications of positive and negative force following a first impulse of half strength, was shown to give seven turns of the tide at the remote end, and therefore eight motions of the relay, following one another at not very unequal intervals of time.

Outline of a Theory of the Structure and Magnetic Phenomena of the Globe. By J. DRUMMOND.

The author, from the admitted fact of our earth having cooled down from an original state of fluidity, and that it now is a solid crust enclosing a fluid mass of molten materials, held that there must be an action of the sun and moon on this fluid mass analogous to that which caused the tides of the ocean; that from thence an outward pressure on the crust must result, propagated along it, in a manner similar to the great tidal wave; and from this principle, in an elaborate essay, he deduced the ordinary magnetic phenomena, as well as volcanoes, earthquakes, and other violent actions; concluding by answering objections which may be urged against the foundation and details of this theory.

Magnetic Experiments made on board the Great Eastern' Steamer.

By W. RUNDELL. (Communicated by Admiral FITZROY.) Admiral FitzRoy exhibited to the Section, and explained tables and a diagram, showing the deviations observed in a compass placed successively at each of eight stations along the deck of the monster iron vessel now building at Millwall.

SOUND.

On a singular Acoustic Phenomenon. By M. DONOVAN, M.R.I.A. The author explained the beats which are experienced when two strings tuned nearly, but not exactly, to unison, are struck at the same time. He then stated that Earl Stanhope had observed these beats in all the tuning-forks tried by him, which he attributed to inequality of the prongs. Earl Stanhope, in consequence, had been at the pains to invent a new tuning instrument. This effect the author often tried to experience, but never could succeed until upon one occasion, just after he had ceased from violent exercise, having applied the fork to his teeth, he distinctly heard the beats. He was thus led to the true origin of the phenomenon, which he could now experience whenever he wished, by running a short distance, particularly up and down stairs. The effect was caused by the beatings of his own heart, which are synchronous with those of the fork.

On the Effect of Wind on the Intensity of Sound.
By Professor G. G. STOKES, M.A., D.C.L., Sec. R.S.

The remarkable diminution in the intensity of sound, which is produced when a strong wind blows in a direction from the observer towards the source of sound, is familiar to everybody, but has not hitherto been explained, so far as the author is aware. At first sight we might be disposed to attribute it merely to the increase in the radius of the sound-wave which reaches the observer. The whole mass of air being supposed to be carried uniformly along, the time which the sound would take to reach the observer, and consequently the radius of the sound-wave, would be increased by the wind in the ratio of the velocity of sound to the sum of the velocities of sound and of the wind, and the intensity would be diminished in the inverse duplicate ratio. But the effect is much too great to be attributable to this cause. It would be a strong wind, whose velocity was a twenty-fourth part of that of sound; yet even in this case the intensity would be diminished by only about a

twelfth part. The first volume of the Annales de Chimie' (1816) contains a paper by M. Delaroche, giving the results of some experiments made on this subject. It appeared from the experiments,-first, that at small distances the wind has hardly any perceptible effect, the sound being propagated almost equally well in a direction contrary to the wind and in the direction of the wind; secondly, that the disparity between the intensity of the sound propagated in these two directions becomes proportionally greater and greater as the distance increases; thirdly, that sound is propagated rather better in a direction perpendicular to the wind than even in the direction of the wind. The explanation offered by the author of the present communication is as follows. If we imagine the whole mass of air in the neighbourhood of the source of disturbance divided into horizontal strata, these strata do not all move with the same velocity. The lower strata are retarded by friction against the earth, and by the various obstacles they meet with; the upper by friction against the lower, and so on. Hence the velocity increases from the ground upwards, conformably with observation. This difference of velocity disturbs the spherical form of the sound-wave, tending to make it somewhat of the form of an ellipsoid, the section of which by a vertical diametral plane parallel to the direction of the wind is an ellipse meeting the ground at an obtuse angle on the side towards which the wind is blowing, and an acute angle on the opposite side. Now, sound tends to propagate itself in a direction perpendicular to the sound-wave; and if a portion of the wave is intercepted by an obstacle of large size, the space behind is left in a sort of sound-shadow, and the only sound there heard is what diverges from the general wave after passing the obstacle. Hence, near the earth, in a direction contrary to the wind, the sound continually tends to be propagated upwards, and consequently there is a continual tendency for an observer in that direction to be left in a sort of sound-shadow. Hence, at a sufficient distance, the sound ought to be very much enfeebled; but near the source of disturbance this cause has not yet had time to operate, and therefore the wind produces no sensible effect, except what arises from the augmentation in the radius of the sound-wave, and this is too small to be perceptible. In the contrary direction, that is, in the direction towards which the wind is blowing, the sound tends to propagate itself downwards, and to be reflected from the surface of the earth; and both the direct and reflected waves contribute to the effect perceived. The two waves assist each other so much the better, as the angle between them is less, and this angle vanishes in a direction perpendicular to the wind. Hence, in the latter direction the sound ought to be propagated a little better than even in the direction of the wind, which agrees with the experiments of M. Delaroche. Thus the effect is referred to two known causes,~ the increased velocity of the air in ascending, and the diffraction of sound.

ASTRONOMY.

On the Distribution of the Orbits of the Comets in Space.
By Cavaliere O. F. MOSOTTI.

The author not being present, this communication was read and explained by Prof. Bolzani. The author commenced by explaining that the simplest and most direct method of analysing the distribution of the comets in space would seem to be, to divide the celestial sphere by means of so many circles parallel to the ecliptic into equal zones corresponding to an aliquot part of the entire superficies, and then to ascertain how many culminating points are contained in each of these. If the orbits were uniformly distributed throughout space, each of them should contain about an equal number of these points; if not, the greater or less number contained in each will serve to show the tendency the orbits have to approach to or recede from that distribution. The author applied this method arithmetically in the first instance; and afterwards, in order to render the results more palpable, reduced them to a graphic construction. The learned Professor then exhibited and explained to the Section, in detail, the several formulæ on which the numerical examination of the question was founded, and then exhibited and explained the graphic construction

reduced to a planisphere. The same planisphere, when properly projected, was made to serve for both the northern and southern hemispheres, by colouring the projecting lines which marked radially on the outer circle the longitudes of the culminating points and of the perihelia for the northern hemisphere blue, and for the southern black; and on each of these radial lines was marked the number assigned to the comet in the catalogue of the 263 discussed by the author. If, then, we conceive these two lines to be produced to the centre, and caused to revolve towards the northern hemisphere if marked with the sign plus, to the southern if marked minus, until they take the position of the inclination of the orbit marked as belonging to each, the position of the two lines will present to the mind a picture of the position which the orbit will hold as well in space as in its own plane. At the end of each of the eight tables, corresponding to the eight zones, were specified the total number of orbits found in that zone, as well as the number of those having their perihelia in the northern or southern hemisphere, and their motion direct or retrograde; combining the data thence given, the author drew up the summary of the whole. He found the orbits to have a tendency to approach in prevailing numbers the polar regions of the ecliptic. The minimum occurs in the fifth zone of each hemisphere. Those whose perihelia are in the northern hemisphere exceed those whose perihelia are in the southern in the proportion of 3 to 2; the number of those having a direct motion to those retrograde as 5 to 6, or nearly equal. The author calls the Great Circle, which passes so as to divide the Milky Way pretty equally, the Galaxy Circle. In the centre of this the sun and earth may be considered to be placed; it cuts the ecliptic towards the solstitial points, and is inclined to it at about 60°. He then finds that the planes of the orbits of the comets are, for the most part, little, if at all, inclined to the plane of the Galaxy Circle, and that they go on decreasing in number as that inclination increases; and therefore he concludes that some cosmical cause must have led to such a result. Also, the perihelia of by far the greater number of those he has discussed are found near the Galaxy Circle, showing that when they are passing most closely under the influence of the sun they are both near the Galaxy Circle, and their proper motion is nearly parallel to its plane. Hence the greater number of comets come to us from the region of the Galaxy itself.

On a Moveable Horizontal Sun-dial, which shows correct Solar Time within

a Fraction of a Minute. By M. DONOVAN, M.R.I.A.

The author first pointed out the inaccuracies incidental to or inseparable from the ordinary horizontal sun-dial, even when executed with the greatest care. He then adverted to the peculiarities of his own dial, showing how it can be placed with the greatest precision in the meridian of the place. After alluding to the defects of the ordinary style, he showed the advantages of substituting a human hair, which, casting a shadow as slender as itself for several inches of its length, affords a line of direction for another hair springing from the same source, which, when stretched through the centre of the most slender part of the shadow, marks the precise time to a few seconds on a large divided circle. One of the peculiarities of this dial is, that it may be placed in any spot illuminated by the sun; an advantage, from which the common horizontal dial is precluded by its being a fixture, and without means of exactly placing its meridian in the meridian of the place.

Tables to simplify and render more general the Method of finding the Time, by observing Circumpolar Stars in the same Vertical. By C. THOMSON. (Communicated by Sir W. R. HAMILTON.)

The author described the tables, and exhibited to the Section a little apparatus constructed by his ingenious assistant, Mr. Thomson, which illustrated the method of observing circumpolar stars for this purpose.

On the Direction of Gravity at the Earth's Surface.

By Professor HENNESSY, M.R.I.A.

If the earth's surface be considered to coincide with that of the liquid which