DIAL ON A CARD.-Somewhere about the end of the year 1759, Ferguson delineated a Dial on a Card, which, when rectified, showed The Hour of the Day,-The Time of the Sun's Rising and Setting,-The Sun's Declination, and the Days on which the Sun entered the Signs of the Zodiac. The original Dial is in our possession, having been kindly presented to us by James L. Rutherfurd, Esq., Edinburgh, in October, 1863. It is done on mill-board -inch thick, 134 inches by 9, covered with foolscap paper (on which the Dial is delineated). James Ferguson, fecit, is lettered in the lower left-hand corner of the dial. On the back of the dial, neatly written by him, are the following directions :—

"How to RECTIFY and USE the DIAL.

Set the cross line on the brass slider to the day of the month, and stretch the thread from thence over the angular point XII, where the curve lines meet; then shift the bead on the thread to that point, and the Dial will be rectified for the following purposes.

1. TO FIND THE HOUR of the DAY WHEN THE SUN SHINES.— Raise the Gnomon (no matter how much or how little), and hold the edge of the Dial next the Gnomon toward the Sun, so as the uppermost edge of the shadow may just cover the Shadow Line; and the bead then playing freely on the face of the Dial (by the weight of a plummet hung occasionally to the thread), will show the time of the day among the hour-lines as it is before or after noon.

2. TO FIND THE TIME OF SUN-RISING AND SUN-SETTING.— Move the thread among the hour-lines, till it either covers some one of them or lies parallel betwixt any two; and then it will cut the time of Sun-rising among the forenoon hour-lines, and of Sun-setting among the afternoon hourlines, for the day of the year indicated by the cross line on the slider.

3. TO FIND THE SUN'S DECLINATION.-Stretch the thread over the angular point at XII, and it will cut the Sun's Declination for the day of the year at which the cross line on the slider stands.

When the bead, rectified as above, moves along any of the curve lines on which the Signs of the Zodiac are marked, the

Sun enters those Signs on the days pointed to by the cross line on the slider.

This Dial answers only for those Places which have the same Latitude with London. To construct such Dials for other Latitudes, see my Mechanical Lectures.-JAMES FERGUSON."

Referring to his "Mechanical Lectures," we find a description of the dial, with two figures, showing how it is constructed. "The Rules for Use" are nearly the same as those already given. What follows, not in the original, but in his Lectures, being important, we give as addenda,

We are told this is "a portable dial, which may be easily drawn on a card, and carried in a pocket-book. The lines a d, a b, and b c, of the gnomon must be cut quite through the card; and as the end a b of the gnomon is raised occasionally above the plane of the dial, it turns upon the uncut line c d as on a hinge. The line dotted A B must be slit quite through the card, and the thread must be put through the slit, and have a knot tied behind to keep it from being easily drawn out. On the other end of this thread is a small plummet, and on the

middle of it a small bead for showing the hour of the day." ("Lectures on Select Subjects in Mechanics," &c.)

In the same year (1759), Ferguson published this Dial on a card 44 inch by 3 inches, having in the left hand lower corner, J. Ferguson, delin. and under it PEREUNT ET IMPUTANTUR. This ingenious Card-Dial has been long out of print, and is very rarely to be had. We, however, understand that it has frequently been copied and sold since Ferguson's time. We are indebted to the kindness of Mr. Robert Sim, Keith, for our copy-it came into his hands from the last relatives of Ferguson in Keith, and is still in excellent preservation; the green silk cord for the plummet and the bead being still attached to it.

We have no other memoranda of Ferguson for 1759, but may add, that as his celebrated work "Lectures on Select Subjects," &c., was published in the following year, it is to be presumed that much of his leisure time, during the later part of 1759 and the beginning of 1760, was devoted to writing that work, and making the drawings necessary for its illustration.

IN MEMORIAM.

1760.

The following memorial-tribute to the worth of a departed friend, was composed by Ferguson in 1760. The original, in his own autograph, written on the inside of the first board of the "Ferguson Bible," Ferguson Bible," so often referred to, is now in the possession of Dr. George of Keith:

"Mr. James Mackenzie of Oxford Road, in the Parish of St. Mary
le bonne, Grocer, died the 11th February 1760, aged 25 years 5 days,
and was interr'd in the same Parish churchyard. He was of solid
Judgment and good sense, remarkably sober, virtuous and constant;
a dutiful son, a loving Bror, and most sincere friend; and may justly
be said to have been a young man of real worth. His soul took its
flight of a Monday a quarter past three o'clock in the afternoon
from this Earth of trouble to a Heaven of eternal Happiness."

Note. One of the pall-bearers at Ferguson's funeral in 1776 is named Mackenzie, probably a relative of the subject of the above record.

"LECTURES ON SELECT SUBJECTS," &c.-In the year 1760, Ferguson published his second-best and celebrated work, Lectures on Select Subjects in Mechanics, &c. Like his Astronomy,

his LECTURES are written in clear and plain language, so much so, that the merest tyro in the sciences of which he treats cannot possibly fail to understand the author's meaning and demonstrations. Until lately, "The Lectures" were the generally acknowledged text-book on Mechanics in Britain, but the now advanced state of the sciences has called into existence other works on the subjects of which it treats. This work has gone through numerous editions. In our memoranda, we have the following editions and dates,-viz. 1st edition, published in 1760,—the 2d in 1764,—the 3d in 1767,— the 4th in 1772,-the 5th in 1776,-the 6th in 1784,-the 7th in 1793; also, republications in 1806,-1823,-1825, and 1827. The edition of 1806 is edited by "David Brewster, LL.D." (now Sir David Brewster) in two volumes. "The Lectures" have also been frequently published in America, and also translated and published in several foreign countries.

he annexed is the title-page of Lectures on Select Subjects.

Lectures on Select Subjects in Mechanics, Hydrostatics, Hydraul-
ics, Pneumatics, and Optics, with the Use of the Globes, the Art of
Dialling, and the Calculation of the Mean Times of New and Full
Moons and Eclipses. Illustrated with Copperplates. By James
Ferguson, London.

MDCCLX.

It is dedicated to "PRINCE EDWARD," in the style so peculiar to last century,—viz.

'To His Royal Highness PRINCE EDWARD, Sir,-As Heaven has inspired your ROYAL HIGHNESS with such a love of ingenious and useful arts, that you not only study their theory, but have often condescended to honour the professors of mechanical and experimental philosophy with your presence and particular favour, I am thereby encouraged to lay myself and the following work at your ROYAL HIGHNESS'S feet; 227 and at the same time beg leave to express that veneration with which I am, Sir, your ROYAL HIGHNESS'S most obliged, and most obedient humble servant, James Ferguson."

227 PRINCE EDWARD was the second son of Frederick, Prince of Wales (eldest son of George H.), was born at Norfolk House on 14th March, 1739. He was seized with a malignant fever at Genoa, in Upper Italy, and died there on September 17th, 1767, aged 28. He was a great patron of the arts and sciences, and had great delight in conversing with Ferguson on Astronomy and kindred subjects; he also occasionally attended Ferguson's lectures.

THE ARMILLARY TRIGONOMETER.-Sometime in the year 1760, Ferguson made a model, in wood, of an Astronomical instrument called The Armillary Trigonometer, the invention of Mr. Mungo Murray, Shipwright, at Deptford.228 It solved the following problems:-" 1st, The Time of the Day, Forenoon and Afternoon, and the Sun's true Azimuth from the South at that time. 2d, The variation of the Compass. 3d, The time of the day being given, to find the Sun's altitude and azimuth at that time. 4th, The time of the Sun's rising and setting, on any day of the year, in any given North latitude less than 664 degrees. 5th, To find when the Morning Twilight begins, and when the Evening ends. 6th, A place being in the north frigid zone (that is, in more than 664 degrees of North latitude), to find on what day of the year the Sun begins to shine constantly on that place without setting; and how long he continues to do so. 7th, How long Twilight continues at the Poles of the Earth. 8th, The Sun's depression below the horizon, at any time of the night, in any given latitude, less than 664 deg. 9th, To find in what North latitude the longest day is of any given length less than 24 hours. 10th, The Sun's amplitude at rising and setting, in any given latitude less than 664 deg. 11th, The length of the longest day being given, at any place whose latitude is North; to find the latitude of that place. 12th, In the Summer months, to find an East and West line; and consequently, a Meridian line, for a place of any given latitude. 13th, The distances of all the Forenoon and Afternoon hours from XII, on a horizontal dial, for any given latitude. 14th, The distances of the Forenoon and Afternoon hours from XII, on a vertical South dial, for any given latitude. 15th, The distances of the Forenoon and Afternoon hours from XII, on a vertical dial, declining from the South toward the East or West, by any given number of degrees."

In Tables and Tracts we are informed, "Mr. Mungo Murray, Shipwright, contrived a very useful instrument which he calls The Armillary Trigonometer;' and I had it some months by me in the year 1757. Since that time, he showed me a paste

228 Mr. Mungo Murray, an ingenious Shipwright, at Deptford, near London. He is the author of an excellent work entitled, "A Treatise on Shipbuilding and Navigation, with numerous Plates and neatly-printed Tables." London, 1754. Price 10s. 6d. Supplement to the Treatise on Shipbuilding, translated from M. Bouguer's "Traité du Naivre." Plates, 3s. London, 1765.