ARITHMETICAL COMPUTATIONS, ]$3 



VIII. 



Upon certain ready Processsesfor Computation, supposed to have . 

 leen invented ly the American Boy exhibited in London*, 



SIR, 



I SHALL make no apology for troubling you on a subject, Introductory 

 which, though generally esteemed dry and abstruse, has ^"^j^'J" 

 at present acquired, from particular circumstances, considerable boy exhibited 

 interest. There is a boy in town, who is exhibited as a curio- m London, 

 sily, from the facility with which he performs several difficult 

 arithmetical operations. It is pretended that this is a gift, and 

 that he has had no instructions to enable him to do this. Now, 

 Sir, 'as there are easy methods of solving these questions, 

 which are not, I believe, generally known, I shall simply state 

 them to the public, that this matter may, if necessary, be 

 further investigated ; and that this boy may be reduced to what 

 he really is — a very clever boy, but no prodigy. 



In extracting the cube root where it cpnsists of three figures, In extracting 

 it is well known that the first figure of the root may be obtained ^{j"^ r ? 0t 

 by a simple inspection of the number of millions, and the last riods, the first 



figure, by observing the final figure of the number whose root period deter- ■ 



a J & 6 mines toe first 



is proposed to be extracted j if then, the middle figure could be figure, and the 



found, we should have the root. To find this, square the final lastdigitdetcr- 

 ^ c , • i f • i iii- mines the 



figure of the root so previously obtained 5 multiply this square last figure, 



by 3, call A the last figure of this product. Now cube the last and the middle 

 r. r , , .. . , . ,. . - , figure is found 



ngure of the root, substract its penultimate digit from the by a simple 



penultimate digit of the number given, (adding ten to this process, 

 last, if it be the smaller of the two) call the result B. 



Then that number, which boin^ multiplied into A, produces 

 a number terminating with the figure B, is the middle figure 

 of the root. An example or two will make it manifest : sup- 

 pose 3/7,933,067 to be proposed; here 7 is the first figure, Example of 

 (as 7 5 = 3'43, the nearest cube below 377) and 3 is the last 

 figure ; since the cube of 3 cerminates with 7, the last figure 

 of the number. Now to find the middle figure 3 3 X3=27. . 

 A=7, and 3 3 =27, of which the penultimate figure is 5. 



* From the Morning Chronicle of Feb. 17, last. For some accouut 

 of Zerah Colburn, See our present voL page 5. 



Now, 



