'306 Of Telegraphic Communication , 
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 en- 
deavoured 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 mi*st*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 prodi- 
gious 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. 
These instruments might have made the signals in ques- 
tion 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 any 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. 
