140 
IOWA ACADEMY OF SCIENCES. 
the negative pole of the second cell, and so on for the 
central line of blocks; a and I are also connected by 
separate wires to a knife-switch. When plugs are inserted 
in the central line of holes (he, de, fg, etc.), the battery 
is in series ready to be charged on closing the knife-switch 
in the circuit. When charged and the knife-switch to the 
dynamo thrown open several combinations are possible 
with the brass bars y and 0 from which wires run to 
another knife-switch connected with the laboratory 
circuit. 
If plugs are inserted at yn and s connecting the first 
cell with the bars y and 2;, the current from that cell 
alone may be used in the laboratory circuit. Two or more 
cells, or the entire battery, may in a similar manner be 
connected in parallel. If a plug is inserted at m, another 
at he and a third at t, the two cells may be discharged 
in series. In a similar manner any two adjacent cells may 
be connected in series, or four may be used in two series of 
two each, or the entire battery used in three series of two 
cells each. If plugs are inserted at m, he, de, fg, and u, the 
first three cells are connected in series. In a similar 
manner any three adjacent cells may be connected in 
series, or the battery as a whole connected in two series of 
three cells each. If plugs are inserted at m, he, de, fg, 
and V, the first four cells are in series. In a similar manner 
any four adjacent cells may be combined in series. Either 
of the two sets of five adjacent cells may also be thus con- 
nected in series, or all six connected in series. 
If one or more of the cells should be removed, the ends 
of the wires that had been connected to the cell can be 
fastened together and the remainder of the battery used in 
series, or in any of the combinations of cells, omitting the 
group to which the cell tha.t has been removed belonged. 
A voltmeter indicates two volts for each cell by itself. 
For the different combinations mentioned the voltages in- 
dicated are four, six, eight, ten and twelve respectively. 
The battery of six cells is arranged in a single line on, a 
shelf close to the switchboard. Should it ever become 
