have a geometrical instrument with tubes, in order that he may know by one of them the right, and by the other the left of him who is to answer. The board must be set up near to this instrument; and to the right and left a solid must be raised ten feet broad, and about the height of a man; in order that the torches, which shall be lifted up over it, may spread a strong clear light; and that when they are to be lowered, they may be entirely hid behind it.

All things being thus disposed on each side, I will suppose, for instance, that advice is to be given, that "An hundred "Cretans, or Kretans, are gone over to the enemy." First he must make choice of such words as will express what is here said in the fewest letters possible, as "Cretans, or Kre"tans, an hundred have deserted," which expresses the very same idea in much fewer letters. The following is the manner in which this information will be given.

The first letter is a K, which is in the second column Two torches must therefore be lifted to the left, to inform the person who receives the signal, that he must look in the second column. He then must lift up five torches to the right, to denote that the letter sought for is the fifth of the second column, that is, a K.

Afterwards four torches must be held up to the left, to point out the Pe which is in the fourth colunin; then two to the right, to denote that this letter is the second of the fourth column. The same must be observed with respect to the rest of the letters.

By this method, every event that comes to pass may be communicated in a fixed and determinate manner.

The reason why two sets of lights are used, is because every letter must be pointed out twice; the first time, to denote the column to which it belongs; and the second, to show its place in order in the column pointed out. If the persons employed on these occasions observe the rules here laid down, they will give exact notice: but it must be practised a long time, before they will be able to be very quick and exact in the operation.

This is what is proposed by Polybius, who, it is well known, was a great soldier and politician, and for this reason his hints ought to be valued. They might be improved, and put in practice on a great many occasions. These signals were employed in a mountainous country.

A pamphlet was lent me, printed in 1702, and entitled, "The Art of making Signals both by Sea and Land." The pamphlet was dedicated to the king, by the Sieur Marcel,

a The figure of it is annexed at the end of this little treatise.

b The words are disposed in this manner in the Greek.

© This is the capital letter R in the Greek tongue.

commissioner of the navy at Arles. This author affirms, that he communicated several times, at the distance of two leagues (in as short a space of time as a man could write down, and form exactly the letters contained in the advice he would communicate) an unexpected piece of news that took up a page in writing.

I cannot say what this new invention was, nor what success it met with; but in my opinion such discoveries as these ought not to be neglected. In all ages and nations, men have been very desirous of finding out and employing methods for receiving or communicating news with speed, and of these, signals by fire are one of the principal.

In the fabulous times, when the fifty daughters of Danaiis murdered all their husbands in one night, Hypermnestra excepted, who had spared Lynceus, it is related that when they escaped by flight, and had each arrived at a place of safety, they informed one another of it by signals made by fire; and that this circumstance gave rise to the festival of torches established in Argos.

Agamemnon, at his setting out for the Trojan expedition, had promised Clytemnestra, that the very day the city should be taken, he would give notice of the victory by fires kindled for that purpose. He kept his word, as appears from the tragedy of Eschylus, which takes its name from that prince; where the centinel, appointed to watch for this signal, declares he had spent many tedious nights in that uncomfortable post.

b

We also find by the writings of Julius Cæsar, that he himself used the same method.

Cæsar gives us an account of another method in use amongst the Gauls. Whenever any extraordinary event happened in their country, or they stood in need of immediate succour, they gave notice to one another by repeated shouts, which were catched from place to place; so that the massacre of the Romans in Orleans, at sunrise, was known by eight or nine o'clock in the evening in Auvergene, forty leagues from the other city.

We are told of a much shorter method. It is pretended that the king of Persia, when he carried the war into Greece, had posted a kind of centinels at proper distances, who communicated to one another, by their voices, such news as it was necessary to transmit to a great distance; and that advice could be communicated from Athens to Susa (upwards of an hundred and fifty leagues) in forty-eight hours.

a Pausan 1. ii. p. 130.

b Celeriter, ut ante Cæsar imperaverat, ignibus significatione facta, ex proximis castellis eo concursum est. Cæs. Bell. Gall. I. ii.

c Col. Rhodig. l. xviij. c. 9,

It is also related, that a " Sidonian proposed to Alexander the Great an infallible method for establishing a speedy and safe communication between all the countries subject to him. He required but five days for giving notice, through so great a distance as that between his hereditary kingdom, and his most remote conquest in India. But the king, looking upon this offer as a mere chimera, rejected it with contempt; however he soon repented it, and very justly; for the experiment might have been made with little trouble to himself.

Pliny relates another method, which is not altogether improbable. Decimus Brutus defended the city of Modena, besieged by Anthony, who kept him closely blocked up, and 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 centinels to him? Of what service were all the nets he spread, when the new Courier took his route through the air.

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 to have been constructed the instrument described by Polybius, for communicating advices at a great distance, by signals made by fire.

AB is a beam about four or five feet long, five or six inches broad, and two or three inches thick. At the extremities of it are, well dove-tailed and fixed exactly perpendicular in

a Vigenere. in his remarks on the seventh book of Cæsar's wars in Gaul, relates this without citing directly the author.

Plin. 1. vij. c. 37.

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

the middle, two cross pieces of wood, CD, EF, 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 (2), whose upper part, which must be cylindrical, and five or six a 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, IK, 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 piece 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 (3) of about an inch round. In the middle of this part (3) 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 CD, EF, this hole must be exactly filled by the projecting and cylindrical part of the screw (2) which 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 board 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 towards the end on the side of the observer, a perforated ring, the aperture of which must be of three or four lines; and at the other end must be placed two threads, the one vertical, and the other horizontal, crossing one another in the axis of the tube.

In the middle of the beam AB must be made a round hole, two inches in diameter, in which must be fixed the foot LM NOP, 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

a Twelfth part of an inch.

circumferentors, theodolites, and even geometrical squares, which are used to draw maps, take plans and surveys, &c. ; but it has the same use, which is to direct the sight.

The person who makes the signal, and he who receives it, must each 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 circumstances 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 have endeavoured is, 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 2, 3, 4, and 5 torches will not be seen at 5, 6, 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 would 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 for the purpose mentioned by Polybius, at a greater distance than two or three leagues. However, I am of opinion, that a city besieged might communicate its wants to an army sent to succour it, or give notice how long time it could hold out a siege, in order that proper measures might be taken; 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.

SECT. VII.

Philopamen 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 lit

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