nomena are observed, in virtue of the same action. If we next stop the electric current in both conductors, and adapt one of the needles to each conductor, they will act upon one another in the same manner as the conductors did upon them.

The apparatus represented in Fig. 11. communicates with the pile, and has its moveable conductor suspended nearly in the same way as in Fig. 1. It differs from it, however, in this, that the two conductors A, B, are here of a spiral form, and the moveable conductor B suspended to a vertical tube of glass. This tube is terminated below, at the centre of the spiral which forms this conductor, and receives in its interior the prolongation of the brass wire of this spiral. When that prolongation reaches D, at the top of the tube, it is then soldered to a copper box F, which carries the copper tube V, into which slides the counter-weight H, and a steel point L, which is plunged in the globule of mercury of the cup Y; whilst the other extremity of the same brass-wire, after having encircled the tube CD in the form of a screw, is soldered to the copper box D, to which is attached another steel point K, to be immersed also in a globule of mercury in the cup X. These two cups are made of steel, in order that they may not be injured by the mercury, and the parts rest on their concave surface, as in Fig. 1.

Scale of the Figures on Plate VIII.

Fig. 1, 2, 3, 5, 9, 10, 11, are drawn in the proportion of one inch to a foot.

Fig. 4. is drawn on a scale of two inches to a foot.

Fig. 6, 7, are on the scale of one inch to a foot, for the parts parallel to the plane of the picture.

Fig. 8. is drawn on a scale of three inches to a foot, for the parts parallel to the plane of the picture.

Erratum in Fig. 1.

For O (placed above B,) read Q, and in

sert C at the angle below X, and D at

the angle below Y, so that CD may designate the conductor above, and parallel to AB.

Ditto in Fig 6. Insert e at the left hand of the dotted lime, so that ef may mark that line.

ART. XXXIII.—Quarterly Abstract of the Diurnal Variation of the Magnetic Needle. By Colonel BEAUFOY, F. R. S.

MONTHLY Mean Variation of the Magnetic Needle.

ART. XXXIV.-Analysis of the Transactions of the Royal Society of Edinburgh, Vol. IX., Part I.

THE part of the Transactions of the Royal Society of Edin

burgh, which has just appeared, contains Eighteen papers, and is illustrated with Thirteen plates. Several of these communications are of a very popular and interesting nature, and may be perused with much pleasure, even by those who are not in the habit of seeking for amusement or information in the Transactions of learned Societies.

1. On the Parallel Roads of Lochaber. By Sir THOMAS DICK LAUDER, Bart. F. R. S. E.; p. 1.-64. With Eight Plates,

In this curious and interesting paper, the author begins by giving a general description of the form and appearance of the shelves or Parallel Roads:-He next suggests the theory which may account for the formation of such appearances in general:He then gives a particular account of the whole shelves of Lochaber, as connected with the topography of the glens where they are found, and he concludes by stating the theory which appears most likely to explain the circumstances of their particular formation.

The Parallel Roads, as they are called, are a series of shelves which extend themselves horizontally along the sides or faces of VOL. IV. NO. 8. APRIL 1821.

D d

the mountains of Lochaber, particularly those which bound the valleys of Glen Gluoy, Glen Roy and Glen Spean.

The highest of these roads or shelves is observed on each side of Glen Gluoy, and in Glen Roy there are three other shelves, the uppermost of which is about 12 feet below that of Glen Gluoy. The second is about 80 feet lower than the first, and the third about 200 feet below the second. The two upper roads of Glen Roy are confined to that valley, but the lowest extends into Glen Spean and round the upper extremity of Loch Laggan. All these different shelves have corresponding ranges in the opposite sides of the valley on the same level, and by means of careful levelling, they were found to maintain the horizontality characterizing the surface of water throughout all the various windings of their linear extent. And whenever an isolated hill happens to rise from the bottom of the valley above the level of any shelf, a delineation runs round the little hill at a level corresponding to that of the shelf on the mountains which bound the glen.

The formation of these roads has been ascribed by tradition to the Kings of Scotland, when the royal residence was in the Castle of Inverlochy, and also to the Fingalians, in consequence of several of the hills being named after the heroes of Fingal. Sir Thomas Lauder, however, considers these opinions as untenable, and attributes the formation of the parallel roads to the action of the waters of a lake which has stood at different heights corresponding with that of the shelves, and which has subsequently burst through its confining barrier, in consequence of some great convulsion which formed at the same time the great glen of Scotland through which the Caledonian Canal is now carried.send

It is very remarkable, that the Parallel Roads should have been so seldom visited even by our own countrymen. If they are works of art, they must possess a high interest in the estimation of the historian and the antiquary; and if they are the result of natural operations, an opinion which we think demonstrable, they afford an ocular proof of a great local convulsion which must have preceded the records of authentic history.

This paper was written before the author had seen the very learned and ingenious Essay of Dr MacCulloch, “On the

Parallel Roads of Glen Roy," published in the fourth volume of the Geological Transactions. The investigations of these able and accurate observers will, we trust, direct the attention of the philosophical geologist to this interesting part of Scotland. 2. On the Poisonous Fishes of the Caribbee Islands. By WILLIAM FERGUSON, M. D. F. R. S. E.; p. 65,-80.

An abstract of this paper has already been given, in vol. i. p. 194,-195. of this Journal.

3. Account of a Mineral from Orkney. By THOMAS STEWART TRAILL, M. D. F. R. S. E.; p. 81,-93.

An abstract of this paper has already been given in this Journal, vol. i. p. 380.

4. Extract from an Inspection Report on the Mud Volcanoes of Trinidad. By WILLIAM FERGUSON, M. D. F. R. Š. E. p. 93,-96.

The Mud Volcanoes described in this paper are situated near Point Icaque, the southern extremity of Trinidad. They occur on a round bare platform of several acres, and resemble chimneys like truncated cones, about three feet high, some of which were throwing out, with a strong bubbling noise, salt water, loaded with argillaceous earth. A white sea-shell was observed in the act of being thrown out along with the mud. The mud was always cold. In the hottest months of very dry seasons, the noise is said to be like that of the loudest cannons, and the mud is thrown up to the height of thirty feet.

5. Memoir on the Repeating Reflecting Circle. By Major-General Sir THOMAS BRISBANE, C. B. F. R. S. E.; p. 97,-102. The observations in this paper, were made with a repeating circle of Troughton's, six inches radius, and divided on gold to 20". For altitudes, Sir Thomas chooses thirty repetitions, divided into three series of ten each, and reads the angle or arc run through during the series. For the time, he has always found six repetitions, sufficient to give it as correct as equal altitudes; aud of these he generally observes three series in order to take the mean. Troughton's circle, six inches radius, gives the same results to a second, as a sixteenth inch repeating circle, with

a moveable axis and level of Reichenbachs. The practical astronomer will find this memoir of great utility.

6. Description of a Fossil Tree found in a Quarry at Niteshill. By the Reverend PATRICK BREWSTER; p. 103,-106. With a Plate.

The trunk of this interesting fossil, which was found in the coal-formation near Paisley, was five feet long, and had four principal roots, each of which was two feet long. The circumference, taken close at the root, was five feet seven inches and a half; in the middle of the stem four feet and a half; and at the top or fracture three feet nine inches.

7. Account of a non-descript Worm (the Ascaris pellucidus) found in the eyes of Horses in India. By ALEXANDER KENNEDY, M. D. F. R. S. Ed. With a Description of the Animal. By Captain THOMAS BROWN, F. R. S. E.; p. 107, -112.

An abstract of this paper will be found in this Journal, vol. ip. 191, 192. The following is Captain Brown's description of it.

ASCARIS pellucidus.-Head slightly subulate, with the extremity somewhat obtuse; body smooth, pellucid, of a bluishwhite colour; thickest at the centre, and gradually tapering towards the head, and abruptly towards the tail, which terminates in a sharp point; its diameter not being more than onefourth of the head. Length, 1 inch.

8. Memoir relating to the Naval Tactics of the late John Clerk, Esq. of Eldin, being a Fragment of an intended account of his Life. By the late JOHN PLAYFAIR, Esq. F. R. S. Lond. & Ed.; p. 113,-138.

It is scarcely necessary to inform our readers, that the celebrated manœuvre of breaking the enemy's line, by the practice of which we have so often annihilated the proudest armaments of France and Spain, was the undisputed invention of our countryman the late John Clerk, Esq. of Eldin, a country gentleman who had no practical acquaintance with naval affairs. Mr Clerk had begun so early as 1779, to make the principles of his system known to his friends. The manœuvre was first successfully practised by Lord Rodney, in April 1782; and it