86 THE STORY-BOOK OF SCIENCE 



is held firm in its iron frame by means of wedges, 

 so that the whole thing seems made of a single block 

 of metal. The bed is then ready for printing. 



"A roller impregnated with a thick ink made of 

 oil and lampblack is passed over the plate. The 

 letters and orthographic signs, which alone stand 

 out in relief, become covered with ink ; the rest does 

 not take it because its surface is lower. A sheet of 

 paper is placed on the inked plate ; it is covered with 

 a pad to protect it, then pressed hard. The ink of 

 the characters is deposited on the paper, and the 

 sheet is found printed on one side. To print the 

 other, the operation is repeated with a second plate. 

 The metal letters are, as I said, carved wrong side 

 before, as the letters of a book appear when you look 

 at them in a mirror. The inky imprint left by them 

 on the paper reproduces them in a reversed position, 

 and consequently in the right way. 



' ' The first sheet is followed immediately by a sec- 

 ond. With the roller the plate is inked again, a 

 sheet of paper is applied, pressure is exerted, and it 

 is done. Then comes a third sheet, a hundredth, a 

 thousandth, indefinitely. All that is needed each 

 time is to ink the plate, cover it with paper, then 

 press. All this is done with such rapidity that in a 

 short time we have a great pile of printed sheets, 

 each of which it would take a whole day to write by 

 hand. 



" Before the invention of this marvelous art, 

 which enables us to reproduce the works of the mind 

 very rapidly and in as great numbers as may be 

 desired, we were restricted to hand-made copies. 



