Abstract :
The paper has for its object the more definite determination of the constants of the liquid rheostat, and the more exact prediction of its performance. First, the phenomena occurring in such a rheostat under a wide variety of circumstances are considered, a distinction being drawn between the behaviour of direct and of alternating currents in the apparatus. Tests are described which bear out and amplify the conclusions, many of which are characterized by the employment, with impunity, of current densities many times larger than those generally considered to fall within the limits of safety. Representative designs of rheostats, for both small and large horse-powers, are described and criticized. A mathematical method is developed for conveniently arriving at the capacity of a given liquid starter, from thermal considerations, which form the deciding factor in this case. A more elaborate calculation is also given, capable of more general application. The effecting of artificial cooling for liquid controllers is dealt with, descriptions of the pipe-cooled and the adjustable weir types being included. The functions of a liquid slip-regulator are analysed and the usual pattern is reviewed, the conclusion being reached that it could be simplified with considerable advantage. Finally, suggestions are made with regard to specifications for governing the design and construction of this apparatus.
