VELOCITY AN EQUIVALENT OF POWER. 149 



Were it practicable to employ the same swift 

 velocity in terrestrial mechanics as in celestial, 

 and to make use of a thread capable of lifting one 

 pound with the swiftness of light (190,000 miles per 

 second), this single thread would serve to transmit 

 1,800,000 horse-power; being more than sufficient 

 to operate all the machinery in Great Britain. 1 



esting extract from the book of Lucretius in "The Guardian," No. 119, 

 and in " The Spectator," No. 231, as follows : 



" Lucretius gives an account of the correspondence between two 

 friends by the help of a certain loadstone, which had such a virtue in it 

 that, if it touched two needles, one of the needles when so touched began 

 to move, and the other at a great distance moved at the same time, and 

 in the same manner. The two friends, being each of them possessed of 

 one of these needles, made a kind of dial-plate, with the twenty-four 

 letters inscribed thereon, as the hours of the day are marked on a dial- 

 plate. Then they fixed one of the needles on each dial-plate, in such a 

 manner as to turn around without impediment over the four-and-twenty 

 letters. They agreed to separate from one another into distant countries, 

 and withdraw themselves punctually into their closets at a certain hour 

 of the day, and to converse with one another by means of their invention. 

 To write any thing to his friend, he directed his needle to each letter 

 that formed the words, making a little pause at the end of words and 

 sentences, to avoid confusion. The friend at the same time saw his own 

 sympathetic needle moving itself to every letter which the needle of his 

 correspondent pointed at. By this means they talked together, and con- 

 veyed their thoughts to one another in an instant over mountains and 

 seas." 



Magnetic needles, mounted as described by Lucretius, are now actu- 

 ally used in operating Wheatstone's telegraph for transmitting commu- 

 nications across oceans. 



1 The system of high speed for transmitting power from motors to 

 machines is now introduced with success, and economy in cost of mate- 

 rial, by substituting light belts and ropes for massive iron shafts. By 

 doubling the velocity of transmission of action to overcome a uniform 

 resistance (like that of gravitation) in a given time, a fourfold effect is 

 produced ; for the double force acts in half the time against half the 

 uniform resistance. Thus by doubling the velocity of a ball projected 

 upward, it ascends fourfold higher. On this basis is established the 

 rule of the increase of effect being produced in the ratio of the squares 

 of the increased velocities. 



