similar parts, whilst in the new or Analytical Engine, they would affect a great many thousand. The Difference Engine might be constructed with more or less advantage by employing various mechanical modes for the operation of addition: the Analytical Engine could not exist without inventing for it a method of mechanical addition possessed of the utmost simplicity. In fact, it was not until upwards of twenty different mechanical modes for performing the operation of addition had been designed and drawn, that the necessary degree of simplicity required for the Analytical Engine was ultimately attained. Hence, therefore, the powerful motive for simplification.
These new views acquired additional importance, from their bearings upon the Engine already partly executed for the Government. For, if such simplifications should be discovered, it might happen that the Analytical Engine would execute more rapidly the calculations for which the Difference Engine was intended; or, that the Difference Engine would itself be superseded by a far simpler mode of construction. Though these views might, perhaps, at that period have appeared visionary, both have subsequently been completely realized.
To withhold those new views from the Government, and under such circumstances to have allowed the construction of the Engine to be resumed, would have been improper; yet the state of uncertainty in which those views were then necessarily involved rendered any written communication respecting their probable bearing on the Difference Engine a matter of very great difficulty. It appeared to Mr. Babbage that the most straightforward course was to ask for an interview on the subject with the Head of the Government, and to communicate to him the exact state of the case.
