Page:Scientific Memoirs, Vol. 3 (1843).djvu/695

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685
L. F. MENABREA ON BABBAGE'S ANALYTICAL ENGINE.

the calculations requisite for arriving at the proposed result. If, for instance, a recurring series were proposed, the law of formation of the coefficients being here uniform, the same operations which must be performed for one of them will be repeated for all the others; there will merely be a change in the locality of the operation, that is it will be performed with different columns. Generally, since every analytical expression is susceptible of being expressed in a series ordered according to certain functions of the variable, we perceive that the machine will include all analytical calculations which can be definitively reduced to the formation of coefficients according to certain laws, and to the distribution of these with respect to the variables.

We may deduce the following important consequence from these explanations, viz. that since the cards only indicate the nature of the operations to be performed, and the columns of Variables with which they are to be executed, these cards will themselves possess all the generality of analysis, of which they are in fact merely a translation. We shall now further examine some of the difficulties which the machine must surmount, if its assimilation to analysis is to be complete. There are certain functions which necessarily change in nature when they pass through zero or infinity, or whose values cannot be admitted when they pass these limits. When such cases present themselves, the machine is able, by means of a bell, to give notice that the passage through zero or infinity is taking place, and it then stops until the attendant has again set it in action for whatever process it may next be desired that it shall perform. If this process has been foreseen, then the machine, instead of ringing, will so dispose itself as to present the new cards which have relation to the operation that is to succeed the passage through zero and infinity. These new cards may follow the first, but may only come into play contingently upon one or other of the two circumstances just mentioned taking place.

Let us consider a term of the form \scriptstyle{ab^n}; since the cards are but a translation of the analytical formula, their number in this particular case must be the same, whatever be the value of \scriptstyle{n}; that is to say, whatever be the number of multiplications required for elevating \scriptstyle{b} to the \scriptstyle{n}th power (we are supposing for the moment that \scriptstyle{n} is a whole number). Now, since the exponent \scriptstyle{n} indicates that \scriptstyle{b} is to be multiplied \scriptstyle{n} times by itself, and all these operations are of the same nature, it will be sufficient to employ