"Niagara falls power Bpptiances, 207 



the same, that the brushes leading out from the 

 transformer will always have impulses of the 

 same polarity delivered to them. In the par- 

 lance of the craft, the transformers that are 

 used to change the voltage from high to low, 

 or vice versa, are called " static transformers," 

 simply because they are stationary, we suppose. 

 The others are called rotary, or moving trans- 

 formers, to distinguish them from the other 

 forms. The operation of the latter is purely 

 mechanical, while the former is electrical. In 

 some instances where the static transformers 

 are very large they develop a great amount of 

 heat, so much that it is necessary to devise 

 means for dissipating it as fast a*s created. 

 In some instances this is done by air-currents 

 forced through them, but in others, where they 

 are very large, oil is kept circulating through 

 the transformer from a tank that is elevated 

 above it, the oil being pumped back by a ro- 

 tary pump into the tank where it is cooled 

 by a coil of pipe located in the oil, through 

 \vhir-h cold water is continually circulating. 

 ]}y thi- means cold oil is constantly flowing 

 down through the transformer, where it ab- 

 sorbs th<- h<-at, which in turn is pumped back 



h<- tank, where it is cooled. 

 Having now traced tin- energy from the 

 water-wheel through the various transforma- 

 tions and havi !U<1 in a very general 

 way the apparatus both for generating elec- 



