181) 



M. Gramme to ariive at a nearer approximation to the 

 continuous current of the voltaic battery than that pro- 

 duced from a magneto-electric machine when rectified by 

 means of a commutator of the ordinary construction. This 

 refinement, the author states, possesses little or no advan- 

 tage in any of the applications of magneto-electricity, when 

 the rectified waves succeed each other at the rate of 5,000 

 per minute, and upwards — a rate of succession easily attain- 

 able, and far exceeded by the machines of Berlioz and 

 Holmes. At this rate the discontinuity of the waves is not 

 distinguishable in the electric light ; nor in the magnetisa- 

 tion of electro -magnets ; nor on galvanometer needles ; nor 

 in electrolytic processes ; and it can only be perceived by 

 the vibrations of a steel spring, placed before the poles of a 

 small electro-magnet, round which the current is trans- 

 mitted. Such instrument would, the author thinks, also 

 indicate similar points of maxima and minima in the current 

 from Gramme's machine. As the armature helices in this 

 machine are each connected with separate pieces of metal, 

 forming the segments of a circle, from which the current is 

 taken by means of ordinary metallic brushes, the number of 

 helices producing currents available for external use, at any 

 given moment, is only a fraction of those constituting the 

 whole circle, and, consequently, for a given weight of mate- 

 rials such a magneto-electric machine must be greatly in- 

 fei'ior in power to machines in which the current is delivered 

 from the whole of the helices simultaneously, as in those 

 hitherto constructed. The substitution by M. Gramme of 

 a commutator Avith multiple segments insulated from each 

 other, and having adjacent segments of the same polarity, 

 while those diametrically opposite have a polarity difierent, 

 requires the same precautions to be taken to prevent the 

 spark at the change of contacts, and is subject to the same 

 wear from friction, as commutators of the ordinary form, in 

 which the segments are united with a common metallic 



