THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES. J 



Akt. I. — A neiv Harmonic Analyzer ; by A. A. Michelson 

 and S. W. Stratton. (With Plate I.) 



Every one who has had occasion to calculate or to construct 

 graphically the resultant of a large number of simple harmonic 

 motions has felt the need of some simple and fairly accurate 

 machine which would save the considerable time and labor 

 involved in such computations. 



The principal difficulty in the realization of such a machine 

 lies in the accumulation of errors involved in the process of 

 addition. The only practical instrument which has yet been 

 devised for effecting this addition is that of Lord Kelvin. In 

 this instrument a flexible cord passes over a number of fixed 

 and movable pulleys. If one end of the cord is fixed, the 

 motion of the other end is equal to twice the sum of the 

 motions of the movable pulleys. The range of the machine is 

 however limited to a small number of elements on account of 

 the stretch of the cord and its imperfect flexibility, so that 

 with a considerable increase in the number of elements the 

 accumulated errors due to these causes would soon neutralize 

 the advantages of the increased number of terms in the series. 



It occurred to one of us some years ago that the quantity to 

 be operated upon might be varied almost indefinitely, and that 

 most of the imperfections in existing machines might be prac- 

 tically eliminated. Among the methods which appeared most 

 promising were addition of fluid pressures, elastic and other 

 forces, and electric currents. Of these the simplest in practice 

 is doubtless the addition of the forces of spiral springs. 



Am. Jour. Sci.— Fourth Series, Vol. V, No. 25.— Jan., 1898. 



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