gether improbable. city of Modena, besieged by Anthony, who prevented his sending the least advice to the consuls, by drawing lines round the city, and laying nets in the river. However, Brutus employed pigeons, to whose feet he fastened letters, which arrived in safety wherever he thought proper to send them. Of what use, says Pliny, were Anthony's intrenchments and sentinels to him? Of what service were all the nets he spread, when the new courier took his route through the air?

Decimus Brutus defended the

Travellers relate, that to carry advices from Alexandria to Aleppo, when ships arrive in that harbour, they make use of pigeons, who have young ones at Aleppo. Letters, containing the advices to be communicated, are fastened about the pigeons' necks, or feet; this being done, the pigeons take wing, soar to a great height, and fly to Aleppo, where the letters are taken from them. The same method is used in many other places.

Description of the instrument employed in signals made by fire.

Mr. Chevalier, mathematical professor in the royal college, a fellow member with me, and my particular friend, has been so good as to delineate, at my request, the figure of the instrument mentioned by Polybius, and to add the following explication of it.

In this manner. I conceive the idea I have of the instrument described by Polybius, for communicating advices at a great distance, by signals made by fire.

A B is a beam about four or five feet long, five or six inches broad, and two or three inches thick. At

i Quid vallum, et vigil obsidio, atque etiam retia amne prætexta profuere Antonio, per cœlum eunte nuntio ?

the extremities of it are, well dovetailed, and fixed exactly perpendicular in the middle, two cross pieces of wood, C D, E F, of equal breadth and thickness with the beam; and three or four feet long. The sides of these cross pieces of timber must be exactly parallel, and their upper superficies very smooth. In the middle of the surface of each of these pieces, a right line must be drawn parallel to their sides; and consequently these lines will be parallel to one another. At an inch and a half, or two inches distance from these lines, and exactly in the middle of the length of each cross piece, there must be driven in very strongly, and exactly perpendicular, an iron or brass screw, whose upper part, which must be cylindrical, and five or six lines in diameter, shall project seven or eight lines above the superficies of these cross pieces.

On these pieces must be placed two hollow tubes, or cylinders, GH, I K, through which the observations are made. These tubes must be exactly cylindrical, and formed of some hard, solid metal, in order that they may not shrink or warp. They must be a foot longer than the cross pieces on which they are fixed,

and thereby will extend six inches beyond it at each end. These two tubes must be fixed on two plates of the same metal, in the middle of whose length shall be a small convexity, of about an inch round. In the middle of this part must be a hole exactly round, about half an inch in diameter; so that applying the plates on which these tubes are fixed, upon the cross pieces of wood C D, E F, this hole must be exactly filled by the projecting and cylindrical part of the screw which

*Twelfth part of an inch.

was fixed in it, and in such a manner as to prevent its play. The head of the screw may extend some lines, beyond the superficies of the plates, and in such a manner as that those tubes may turn, with their plates, about these screws, in order to direct them on the boards or screens P, Q, behind which the signals by fire are made, according to the different distances of the places where the signals shall be given.

The tubes must be blacked within, in order, that when the eye is applied to one of their ends, it may not receive any reflected rays. There must also be placed about the end, on the side of the observer, a perforated ring, the aperture of which must be of three or four lines; and place at the other end two threads, the one vertical, and the other horizontal, crossing one another in the axis of the tube.

In the middle of the beam A B, must be made a round hole, two inches in diameter, in which must be fixed the foot L M N O P, which supports the whole machine, and round which it turns as on its axis. This machine may be called a rule and sights, though it differs from that which is applied to circumferenters, theodolites, and even geometrical squares, which are used to draw maps, take plans, and survey, &c. but it has the same uses, which is to direct the sight.

The person who makes the signal, and he who receives it, must have the like instrument; otherwise, the man who receives the signal could not distinguish whether the signals made, are to the right or left of him who makes them, which is an essential circumstance, according to the method proposed by Polybius.

The two boards or screens P Q, which are to denote the right and left hand of the man who gives the signals, or to display or hide the fires, according to the circumstance of the observation, ought to be greater or less, and nearer or farther distant from one another, according as the distance between the places where the signals must be given and received, is greater or less.

In my description of the preceding machine, all I endeavoured was, to explain the manner how Polybius's idea might be put in execution, in making signals by fire; but I do not pretend to say, that it is of use, for giving signals at a considerable distance; for it is certain, that, how large soever this machine be, signals made by two, three, four, and five torches, will not be seen at five, six, or more leagues distance, as he supposes. To make them visible at a greater distance, such torches must not be made use of, as can be lifted up and down with the hand, but large wide spreading fires, of whole loads of straw or wood, and consequently, boards or screens of a prodigious size must be employed, to hide or eclipse them.

Telescopes were not known in Polybius's time; they were not discovered or improved till the last century. Those instruments might have made the signals in question visible, at a much greater distance than bare tubes could have done; but I still doubt, whether they could be employed to the use mentioned by Polybius, at a greater distance than two or three leagues. However, I am of opinion, that a city besieged, might communicate advice to an army sent to succour it, or give notice how long time it could hold out a siege, in

order to taking proper measures; and that, on the other side, the army sent to its aid might communicate its designs to the city besieged, especially by the assistance of telescopes.

SECTION VII.

PHILOPEMEN GAINS A FAMOUS VICTORY NEAR MANTINEA, OVER MACHANIDAS, TYRANT OF SPARTA.

THE Romans,' wholly employed in the war with Hannibal, which they resolved to terminate, intermeddled very little with that of the Greeks, and did not molest them during the two following years.

In the first, Philopemen was appointed captain general of the Acheans. As soon as he was invested with this employment, which was the highest in the state, he assembled his allies before he took the field and exhorted them to second his zeal with courage and warmth, and support with honour both their fame and his. He insisted strongly on the care they ought to take, not of the beauty and magnificence of the dress, which became women only, and those too of little merit; but of the neatness and splendour of their arms, an object worthy of men, intent upon their own glory and the good of their country.

His speech was received with universal applause, insomuch that, at the breaking up of the assembly, all those who were magnificently dressed were pointed at; so great an influence have the words of an illustrious person, not only in dissuading men from vice, but in

I A. M. 3798. Ant. J. C. 206.

m

Polyb. 1. xi. p. 629–631.