342 LETTERS ON NATURAL MAGIC. 



cannot fail to prove extensively useful in various branches 

 of the mechanical arts. 



The drawings of this machinery, which form a large 

 part of the work, and on which all the contrivance has 

 been bestowed, and all the alterations made, cover upwards 

 of 400 square feet of surface, and are executed with ex- 

 traordinary care and precision. 



In so complex a piece of mechanism, in which inter- 

 rupted motions are propagated simultaneously along a 

 great variety of trains of mechanism, it might have been 

 supposed that obstructions would arise, or even incompa- 

 tibilities occur, from the impracticability of foreseeing all 

 the possible combinations of the parts ; but this doubt has 

 been entirely removed, by the constant employment of a 

 system of mechanical notation invented by Mr. Babbage, 

 which places distinctly in view, at every instant, the pro- 

 gress of motion through all the parts of this or any other 

 machine, and by writing down in tables the times required 

 for all the movements, this method renders it easy to 

 avoid all risk of two opposite actions arriving at the same 

 instant at any part of the engine. 



In the printing part of the machine less progress has 

 been made in the actual execution than in the calculating 

 part. The cause of this is the greater difficulty of its 

 contrivance, not for transferring the computations from 

 the calculating part to the copper or other plate destined 

 to receive it, but for giving to the plate itself that number 

 and variety of movements which the forms adopted in 

 printed tables may call for in practice. 



The practical object of the calculating engine is to 

 compute and print a great variety and extent of astronomi- 

 cal and navigation tables, which could not be done with- 

 out enormous intellectual and manual labour, and which, 

 even if executed by such labour, could not be calculated 

 with the requisite accuracy. Mathematicians, astronomers, 



