5 creuzers, or 24 d. a bottle. It belongs to the Abbot of Constance, and is chiefly consumed in Germany. Sexard is on the Danube, between Buda and Esseh. 3. The Erlaw wine, which is reckoned at Vienna almost equal to that of Buda. Erlaw is in Upper Hungary, south-west of Tokay, between 47 and 48 degrees of latitude. 4. The Gros Wardein wine, a strong bodied wine, and very cheap. It belongs chiefly to the Duke of Modena, whose ancestor got a large estate in this country, in grant from the Emperor Leopold, as a reward for his services in the Hungarian wars. Gros Wardein is an old fortress near the confines of Transylvania, between 46 and 47 degrees of latitude.

XXXIII. On the Figure and Composition of the Red Particles of the Blood, commonly called the Red Globules. By Mr. Wm. Hewson, F. R. S. p. 303. This paper is reprinted in Mr. Hewson's collected works.

XXXIV. On the Effects of a Thunder-storm, March 15th, 1773, on the House of Lord Tylney at Naples. In a Letter from the Hon. Sir Wm. Hamilton, F.R.S. Dated Naples, March 20, 1773. p. 324.

This accident was on his lordship's assembly night; so that most of the nobility of this country, many of the foreign ministers, foreigners of distinction, particularly English, were present at the time of the explosion; there were not less than 250 in the apartments; and including servants, the whole number under Lord Tylney's roof could not be less than 500. The lightning passed through 9 rooms, 7 of which were crouded with parties at cards, or conversing; it was visible in every one, notwithstanding the quantity of candles, and has left in all evident marks of its passage. Many of the company were sensible of a smart stroke, like that of electricity, and some complained for several days after of a pain they felt from that stroke, but no one received any essential hurt; a servant indeed of the French ambassador's house has a black mark on his shoulder and thigh, from a stroke he received on the staircase; and another servant, who was asleep on the same staircase, his head reclining against the wall, had the hair entirely singed from it on that side.

The confusion at the moment was very great: the report, which seems to have been equally heard in every room, was certainly as loud as that of a pistol; and every one flying the room they were in, thinking the danger there, met of course in the door-ways, and stopped all passage. A Polish prince, who was playing at cards, hearing the report, as he thought of a pistol, and feeling himself struck, jumped up, and clapping his hand to his sword, put himself in a posture of defence. Sir Wm. H. was sitting on a card-table, and conversing with M. de Saussure, Professor of Natural History at Geneva; they happened to be looking different ways, and each thought that the bright light and report was immedi

ately opposite to him; and every one was persuaded that the greatest explosion had been directly before himself. Hearing however a voice saying, un fulmine, un fulmine! they began to examine the gallery in which they were, and soon discovered that the gilding of the cornish had been affected, for in the corners, and at every junction, it was quite blackened; those that had been sitting under the cornishes were covered with the shining particles of the varnish that went over the gilding, and which was thrown off in small dust, at the moment of the explosion. In the apartment above, the same operation had been performed on the gildings; and it is certain that the profusion of gildings, and the bell-wires, prevented the lightning from making more use of the company to conduct it in its course. For further particulars, see Sir Wm. Hamilton's Essays collected.

XXXV. On some Improvements in the Electrical Machine. By Dr. Nooth.

P. 333.

It is evident, that the electric matter is excited in the instant that the glass passes over the rubber, and that it becomes sensible to us by its adhering to the revolving surface of the glass. It also appeared highly probable, that the quantity of fire, which we find on the glass in motion, is not the whole of that which is excited by the passage of the glass on the rubber. The luminous appearance in the angles between the glass and rubber, and which is extremely distinct in a dark room, rendered it next to certain, that a part of the excited electric fluid returns immediately to the cushion without performing a revolution with the glass; and that of course a circulation of the fire is thus kept up in the substance of the cushion in the common method of constructing the machines.

To be convinced of this, Dr. N. attempted to make the passage of the fire from the glass to the anterior part of the cushion, or to that part which corresponds with the ascending side of the cylinder, demonstrable, by placing a piece of silk between the glass and cushion. This silk was larger than the cushion; and part of it was allowed to adhere, by the attraction of the electric fire, to the ascending part of the cylinder. His view in doing this was to cut off, in that part, the immediate communication between the excited glass and cushion, and by that means render the circulation of electric matter visible, which he suspected to take place in the machine; as it was thus forced to turn over the loose edge of the silk before it could return to the cushion. The event answered his expectation; and he then perceived, that the greatest part of the excited fluid was commonly re-absorbed by the fore part of the cushion without becoming sensible on the superior part of the glass.

Having thus verified his supposition by actual experiments with silken flaps of different sizes, he endeavoured to discover a method of preventing that circulation of the electric fluid, and if possible, of obliging the whole, or the greater part of it, that is once excited, to make the revolution with the glass. This

indeed the silk, when of considerable breadth, in some measure effected; but he thought that this obstruction to the immediate return of the fire might be rendered more complete by increasing the thickness of the silk, or by applying to it some nonconducting substance, that might confine the excited fluid more. perfectly to the surface of the revolving cylinder. Bees-wax being a nonconducting substance easily procured, he rubbed the silken flap with it, and found that the return of the fire to the cushion at the anterior part of the machine was by that means much diminished, and consequently the excitation of the glass was apparently increased. The addition however of more silk was still more effectual, in confining the fire to the glass; and when it was employed 10 or 12 times doubled, it seemed to deny any passage from the glass to the cushion.

As Dr. N. thus discovered the method of remedying the common defect in the construction of the anterior part of the cushion, he next attended to that part which corresponds with the descending side of the cylinder. Being convinced that this part of the rubber was alone concerned in the excitation, he imagined that the reverse of what was necessary anteriorly should be adopted in the structure of the posterior part; that instead of placing nonconducting substances be-, tween the glass and cushion, we should here make the afflux of the electric matter as great as possible, by the application of the most perfectly conducting bodies. Confining therefore the amalgam to that place where the glass first comes in contact with the rubber, he placed some tinfoil close to the amalgam, and bending it back, secured it to the metallic plate below the cushion. By this means the electric matter found an easy access to the place of excitation; and the effect of the machine was thereby greatly increased. A piece of leather, covered with amalgam, and fixed to the posterior part of the rubber, in such a manner as to allow about an inch of it to pass under the cylinder, answered every purpose of the tinfoil; and, as it was not liable to be corroded by the mercury, like tinfoil, it was on that account much preferable.

From the above experiments it was apparent that the excitation was altogether performed by the posterior portion of the cushion; and that the anterior part, when made of conducting substances, re-absorbs the greater quantity of the excited matter. In the structure therefore of electrical machines, we should always have a free electric communication behind, to facilitate the excitation; and the most perfectly nonconducting substances before, to prevent the re-absorption. To answer these intentions, it will perhaps be advisable to make the cushion of silk, stuffed with hair, and to lay some metallic conductor round the posterior part, that a free access may be allowed to the electric matter coming to the place of excitation from the inferior part of the machine. Cushions, made in this manner, and then covered with silk 10 or 12 times doubled, are much more powerfully excitant than any others that he had yet tried. Various other methods 3 N

VOL. XIII.

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however may be pursued in the construction of the rubber; but it should be an invariable rule, to place nonconducting bodies before, and conducting substances behind, the cylinder. From the preceding principles, it follows, that the port to the rubber should likewise have its conducting and nonconducting side. For this purpose, it may be necessary to employ baked wood, and to cover the posterior half with tinfoil. The place of excitation will be thus sufficiently supplied with electric matter, and the cylinder will not be robbed of a part of the excited fire, before that fire has made a revolution with the glass.

By attending to the place where the excitation is effected, it must appear evident, that the amalgam is only to be laid on the posterior part of the cushion; its presence indeed would be useless, if not injurious, in any other situation. It will however be found somewhat difficult to confine the pure amalgam to the posterior part of the rubber; but if it is mixed with a little hair powder and pomatum, it pretty well keeps its place. The strewing the amalgam thus prepared on the glass, as it revolves, is perhaps the best method of applying it; as, by that means, it is in a great measure prevented from passing on to the nonconducting substances that are placed before. Should any of the amalgam be carried forward by the revolution of the glass, it should be carefully removed. The necessity of keeping that part free from conducting bodies cannot be too much insisted on; and when fresh amalgam is applied as before mentioned, to the proper part of the rubber, the flap should be held down during half a dozen turns of the machine, lest it might collect some of the amalgam before it is properly fixed. It is a probable conjecture that, when the flap of silk is covered with amalgam, part of the amalgam, which is not immediately subservient to the excitation, acts as a conductor in restoring the fire again to the cushion; and that thus, by an improper disposition of it, we suppress, instead of increasing, the quantity of the excited matter.

In short, when an electrician attends to the preceding principles in the construction of his rubber, and to the proper disposition of the amalgam, he has nothing to fear from the humidity of the atmosphere, as his machine will work equally well in all kinds of weather. The rest of the electrical apparatus may be made according to the directions that have been given by the different electrical writers. Each has had his favourite machine; and perhaps no one has been yet. contrived that has not had its peculiar advantages.

XXXVI. Properties of the Conic Sections; deduced by a Compendious Method.. Being a Work of the late Wm. Jones, Esq., F.R.S., which he formerly communicated to Mr. J. Robertson, Libr. R. S., and by him addressed to the Rev. N. Maskelyne, F.R. S., &c. p. 340.

It is well known that the curves formed by the sections of a cone, and there

fore called conic sections, have, from the earliest ages of geometry, engaged the attention of mathematicians, on account of their extensive utility in the solution of many problems, which were incapable of being constructed by any possible combination of right lines and circles, the magnitudes used in plane geometry. The properties of these curves are become far more interesting within the last 2 centuries, since they have been found to be similar to those described by the motions of the celestial bodies in the solar system.

Two different methods have been taken by the writers who have treated of their properties; the one, and the more ancient, is to deduce them from the properties of the cone itself; the other is to consider the curves, as generated by the constant motion of 2 or more straight lines moving in a given plane, by certain laws. There are various methods of generating these curve lines in plano; one method will give some properties very easily; but others, with much trouble: while, by another mode of description, some properties may be readily derived, which, by the former, were not so easily come at: so that it appears there may be a manner of describing the curves similar to the conic sections, by the motion of lines on a plane, which in general shall produce the most essential properties, with the greatest facility.

That excellent mathematician, the late Wm. Jones, Esq. F.R.S. had drawn up some papers on the description of these curves, or lines of the second kind, very different from what he gave in his Synopsis Palmariorum Matheseos, published in the year 1706; or from that of any other writer on this subject. A copy of these papers he let Mr. R. take about the year 1740, who, though they

were in an unfinished state, thought them of too much consequence to be lost; and therefore was desirous of preserving them in the Phil. Trans. in the manner he at first transcribed; though he is aware they might have been put into a form more pleasing to the generality of readers: Mr. R. indeed annexed larger diagrams than what accompanied the author's copy, in order to render the lines more distinct, as all the relations are to be represented in a single figure, of each kind. Mr. R. then proceeds to state that Mr. Jones, having laid down a very simple method of describing these curves, seems to have been desirous of arriving at their properties in as expeditious a way as he could contrive; and therefore he has used the algebraic method, in general, of reducing his equations; and on some occasions has used the method of fluxions, to deduce some properties chiefly relating to the tangents; and by a judicious use of these, he has very much abridged the steps which otherwise he must have taken, to have deduced the very great variety of relations he has obtained: these he intended to have arranged in tables, whence an equation expressing the relation between any 3 or more lines of the conic sections, might be taken out as readily as a logarithm out of their tables; this he has only partly executed; but it may easily be con