1896.] 



on Hysteresis. 



229 



the coal burnt at the central station, after having its energy passed 

 through a series of costly conversions, was devoted in the end to 

 nothing more than uselessly warming the transformers in the cellars 

 of consumers or in boxes under the streets. So long as iron could 

 not be found that was destitute of magnetic hysteresis, some loss on 

 this account was inevitable ; but it might be greatly lessened by 

 choosing a suitable kind of iron. Experience showed that some kinds 

 of iron had much less hysteresis than others. Thus in Fig. 4 the 

 curve marked I related to a specimen of iron eminently suitable for 

 use in transformers, while the curves marked II and III related to 

 other brands of iron. They enclosed much larger areas, and showed 



Fig. 4. 



that the iron which gave them was to be avoided as having too much 

 hysteresis. Of late years some of the makers of iron had striven 

 with marked success to produce iron which should be comparatively 

 free from hysteresis, and it was now possible to obtain material 

 for transformers which reduced the loss to a fraction of what was 

 formerly thought inevitable. 



The lecturer's magnetic curve tracer was exhibited in action, 

 showing magnetic curves, similar to Fig. 3, upon a screen by giving 

 to a small mirror simultaneous horizontal and vertical movements, 

 the former proportional to the magnetising force, and the latter to 

 the magnetisation of the specimen of iron in the machine. As a 



