DYNAMO-ELECTRIC MACHINES. 93 



before passing through the remainder, is not absolutely necessary, as 

 it may traverse the whole of the coils before performing any other 

 duty. It has been found, however, that when the machine is thus 

 working that the current is more regular and not subject to the 

 irregularities arising from varying resistance, as it would be if the 

 whole current traversed the magnet coils first. Unlike magneto- 

 electric machines, whose power increases simply as the increase of 

 speed, dynamos, in a perfect type of machine, increase in a geomet- 

 rical ratio. Magnetic intensity of the field magnets varies with all 

 the varying circumstances surrounding it. If the speed is decreased 

 the current is decreased, and as the intensity of the field depends 

 upon the current by decreasing it, the intensity of the field is dimin- 

 ished also. As the speed of the armature is increased the intensity 

 and electro motive force of the current is increased in the same ratio. 

 This reacts upon the electro magnets, increasing the intensity of the 

 field, and so increasing both the electro motive force and the inten- 

 sity of the current, so that if it was possible to construct a perfect 

 machine, and what is understood by that is one in which there was 

 no loss either from friction, or sparks, or varying resistance, or any 

 other cause, the resultant effect of an increase of speed would be in 

 the ratio of the cube of such increase. In other words, its power 

 would be in the ratio of the cube of its speed. It was found by 

 actual measurement that a Gramme machine of the normal type, 

 running at eight hundred revolutions per minute, gave nearly double 

 the light when increased to a speed of 1000. Now the ratio of the 

 cubes of those numbers are to each other as 512 is to 1000, so that 

 the light produced was nearly equal to the ratio of the cubes of the 

 speeds. The actual amount of light, at 800 revolutions, was 730 

 bees, at 1000 revolutions it was 1292 bees, their ratio is 1.77. The 

 ratio of 512 to 1000 is 1.95 so that the rate of increase of light as 

 compared to the cube of the increased speed, was in the ratio of 1.77 

 to 1.95. It must be born in mind,, however, that the passive resist- 

 ances of the machine, at the different speeds, were very nearly the 

 same. The resistance of the machine itself, the conductor to and 

 from the lamps, and the lamps themselves, were the same. There 

 was an increase of resistance at the commutator, due to increased 

 friction, and an increased loss due to an increased sparking. You 

 see what a great difference there is in the dynamo over the magneto-- 



