6 SEC. 1. ARITHMETIC. 



21. Calculating Machine, designed by Viscount Mahon, 

 afterwards third Earl Stanhope (1753-1816), and constructed by 

 James Bullock in 1775. Formerly belonging to Mr. C. Babbage, 

 F.E.S. Major- General Babbage. 



22. Calculating Machine, designed by Viscount Mahon, 

 afterwards third Earl Stanhope (1753-1816), and constructed by 

 James Bullock in 1777. Formerly belonging to Mr. C. Babbage, 

 F.R.S. Major- General Babbage. 



23. Babbage's Calculating Machine ; or Difference 

 Engine. H.M. Board of Works. 



This machine was invented by the late Mr. Charles Babbage, F.R.S., who 

 was born on the 26th December 1791, and died on the 18th October 1871. 



Its construction was commenced in 1823 by authority, and at the cost of 

 the Government, and was carried on for several years under Mr. Babbage' s 

 gratuitous supervision. The work was suspended in 1833, and after many 

 delays, Mr. Babbage was informed in November 1842 that the Government 

 regretted the necessity of abandoning the machine, alleging the expense of 

 its completion as the ground for their decision. 



At the time of its suspension about 17,000/. had been expended by Govern- 

 ment upon its construction, and a large part of the machinery had been 

 made. The small portion now exhibited was put ogether in 1833, prior to 

 the suspension of the work, in order to show the action of the machinery. 



The whole engine, when completed, was intended to have had 20 places of 

 figures and 6 orders of differences. 



This machine was expressly designed for the purpose of calculating and 

 printing tables, and not to perform single arithmetical sums. 



If a single article is wanted, it is not, generally speaking, worth while to 

 construct a machine to make it ; but, when large numbers are required, their 

 production comes within the true province of machinery, and in this sense the 

 Difference Engine is emphatically a machine for manufacturing tables. 



The mode in which the Difference Engine calculates tables is, by the con- 

 tinual repetition of the simultaneous addition of several columns of figures to 

 other columns, in the manner more particularly described below, and printing 

 the result. 



In the small portion put together, and now exhibited, the figure opposite 

 the index on the .lowest wheel visible, in all cases, represents units ; the 

 figure on the next wheel above, tens ; that on the one above it, hundreds ; 

 the next thousands, and so on. 



The right hand column of wheels shows the result of the calculation or the 

 tabular number ; for instance, series of squares, cubes, or logarithms, &c. 

 appear upon it, according to the nature of the calculation the machine is 

 making. 



The next or central column represents the First Difference, and the left 

 hand column the Second Difference. At the bottom of the central column is 

 a figure wheel, covered, which can be used as a third difference, so as to 

 enable this portion of the machine to calculate tables of which the Third 

 Difference does not exceed 9. This will be better understood if this last 

 wheel is supposed to represent the lowest wheel of a fourth column of figures 

 standing beyond the left hand side of the machine, as it would be if it formed 

 part of the complete machine. 



This arrangement is effected by a movable platform, with axles, and gearino- 

 wheels upon them, which are used for adding from the third difference wheel 



