128 THE FIELD OF EXPERIMENTAL RESEARCH. 



Planto rhcostatic machines, the condenser plates of which are charged 

 in parallel from 10,000 small storage cells connected in scries. The 

 discharge of the condenser plates is effected after they are connected 

 in series l\v a suitable connection changing frame moved for the pur- 

 pose. Very high potential discharges are thus obtained and the polarity 

 is always definite. It is manifest that the size of the apparatus and 

 the perfection of its insulation determine the possible performance. 

 The objection to such an apparatus for experimental research or demon- 

 stration is the large number of cells required and the complicated 

 arrangements of circuits for charging them. I have, however, recently 

 succeeded in removing all necessity for the presence of charging cells, 

 and have produced what may be temied a dynamostatic machine which 

 is worked by power or by current from a lighting circuit, either con- 

 tinuous or alternating, and may replace a static machine. It is, of 

 course, not dependent upon the weather. I trust it may be of suffi- 

 cient interest to merit the following brief description: A small electric 

 motor has, in addition to its conunutator. a pair of rings connected to 

 its armatuiv winding for o))taining alternating currents. The shaft 

 of the motor drives synchronously a revolving frame bearing connec- 

 tions which, as in the Plante rhcostatic machine, connect a series of 

 condenser plates alternately in })arallcl foi' charging and in series for 

 discharging at high potential. A small oil-immersed step-up trans- 

 former has its primary connected to the l)rushes bearing upon the two 

 alternating current rings of the motor, and its secondary, giving say 

 20,000 volts, is periodically connected to the condenser plates while in 

 parallel, by means of the revolving connection frame. The adjust- 

 ment is such that only the tops of the alternating waves or their 

 maxima are used to charge the condenser plates, while, also, those 

 halves of the Avaves which are of the same polarity are alone used, the 

 others being discarded or left on open circuit. The appai'atus may be 

 driven by power, in which case the electric motor becomes a dynamo, 

 exciting its own field and supplying alternating current to the primary 

 of the step-up transfoi'mer, or suitable alternating currents ma}^ drive 

 it as a synchronous motor. Such a machine, run by continuous cur- 

 rents and having onl}' eleven plates, gives sparks betAveen its terminals 

 over 12 inches long in rapid succession. It can be built cheaph', and 

 is a highly instructive machine from the transformations it illustrates. 



The machine is also arranged by the addition of a simple attach- 

 ment so that it ma}^ be used to charge insulated bodies, or to charge 

 Leyden-jar condensers or the like, replacing the ordinary static 

 machines. It might, in fact, be used to charge a second range of con- 

 denser plates in another rhcostatic machine to a potential of 100,000 

 volts, for example. These, after coupling in series or cascade, might 

 be made to yield potentials beyond any thus far obtained. 



The interest in such experimental apparatus and the results obtained 



