IOWA ACADEMY OF SCIENCES. 
141 
desirable to increase the capacity without purchasing larger 
cells a second series of cells may be placed on a shelf below 
the one now used and each pole of the cells now placed may 
be connected with the corresponding pole of a cell on the 
shelf below, thus requiring no change whatever in the 
switchboard. 
It is possible to short-circuit the first ceil by inserting 
plugs at m, he and n. In a similar w^ay any one ceil, or any 
series of successive cells up to five in number, may be short- 
circuited. There is, however, no difficulty experienced, for 
no combination that will short-circuit a cell is required, 
and if made by accident during the time it takes to adjust 
the plugs the mistake does no harm. A ceil left short- 
circuited for five minutes dropped in voltage from two to 
one and one-half, but in another five minutes it had re- 
gained its original voltage. 
The rotary transformer itself is very convenient for even- 
ing work. By means of a starting rheostat which is also 
a speed controller various voltages may be secured. A 
series of tests gave the following voltages: 10^, 1L|, 12|, 
13|, 14, 14i, 14|, 15. The amperage necessary to run the 
motor dropped from close to 3| when the lO^ volts were 
generated to about 2| when the 15 volts were generated. 
Opposite segments of the motor are tapped to collector 
rings from which an alternating current may be carried to 
the laboratory circuit through a separate switch when an 
alternating current is desired. A four-inch pulley attached 
to the axle of the motor makes it possible to obtain power. 
Ir is expected that when a gasoline engine is secured the 
motor will serve as a dynamo, thus giving three dynamos 
of different voltages from any one of which a current may 
be obtained. 
