1076 
DR. C. W. SIEMENS ON THE DYNAMO-ELECTRIC CURRENT. 
5'5 m.m. wire, each having 32 convolutions, and therefore the four bobbins a total of 
512 convolutions with a resistance of '3065 S. U. 
The accompanying Tables Nos. 5, 6, 7, 8, and 9 give the details of the experiments 
made, which are shown graphically in the diagrams similarly numbered. The current 
in webers was simply calculated by multiplying the square root of the reading on the 
electro-dynamometer with the constant of the instrument, i.e., 2'3323. 
To be able to calculate the electro-motive force from the current in webers and 
resistance in Siemens’ units, it was necessary to convert the S. U. into C. G. S. units 
by multiplying the same by '9337 X 10 9 . (This figure is given by Lorenz, Pogg. Ann., 
Bd. cxlix., 1873.) By again multiplying this resistance into the current we get, 
according to Ohm’s law, the electro-motive force in C. G. S. units, and by dividing by 
10 8 we get the E. M. F. in volts. 
I have further calculated the total amount of work developed in the following 
manner : — 
Work done =ExCxf or, which is the same, C 2 xRX£, where E is E. M. F; 
C, current; R, resistance ; t, time. 
From these calculations t is eliminated as it occurs in all the equations. 
1 volt=10 8 C. G. S. units. 
1 weber^yg- C. G. S. unit of current. 
1 PIP = 7'46 X 10 9 C. G. S. units. 
Therefore 
1 volt x 1 weber_10 8 x 10 -1 x 
1 HP ~7-±QxIW~ 1t * 
and if we multiply the E. M. F. in volts by the current in webers, and divide by 746, 
we have the actual work developed in horse-power. 
To find the actual work done in the outside resistance we use the formula C 3 xR, 
of course having to reduce the resistance R into absolute C. G. S. units by multiplying 
by -9337 X 10°. 
The machine with the new winding had a helix with 24 part commutator wound 
with 312 convolutions of 2'8 m.m. wire. 
The electro-magnets being lengthened by 2” to take bobbins lOg”, instead of 8b” as 
on the ordinary machines, I had three sets of bobbins made, and had the same wound 
with different sizes of wire, viz. : 2'5 m.m., 2’8 m.m., and 3 m.m., having a respective 
resistance of 11 ‘26, 7'563, and 4'46 S. U. 
The accompanying Tables Nos. 1, 2, 3, and 4 show the experiments made with this 
machine with electro-magnets of 11 '26 S. U. resistance; Nos. 10, 11, 12, and 13 with 
electro-magnets of 7'563 S. U. ; and Nos. 14 and 15 with electro-magnets of 4'46 S. U. 
The helix in all cases having been wound with 2'8 m.m. wire with a resistance of 
"234 S. U. when measured in the machine. 
The Tables marked 5, 6, 7, 8, and 9 refer to the dynamo machine wound in the 
ordinary way. 
