139 
M. Gramme to arrive 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- 
ferior 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 with multiple segments insulated from each 
other, and having adjacent segments of the same polarity, 
while those diametrically opposite have a polarity different, 
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 
