DRS. J. AND E. HOPKINSON ON DYNAMO-ELECTRIC MACHINERY. 
351 
In Table I. column I. is the speed of the dynamos; column II. is the reading of the 
spring in grammes; column III. is the power transmitted by the belt in watts; 
column IV. is the potential at the terminals of the generator; column V. is the 
current passing in the external circuit between the two machines; column VI. is the 
resistance introduced into the magnets of the motor by the rheostat; column VII. is 
the power absorbed in the armature of the generator; column VIII. is the power 
absorbed in the armature of the motor; column IX. is the power absorbed in the 
magnets of the generator; column X. is the power absorbed in the magnets of the 
motor; column XI. is the power absorbed in the connecting leads between the two 
dynamos, in the rheostat resistance r, and in the standard resistance used for measur¬ 
ing the current; column XII. is the total electrical power developed in the generator; 
column XIII. is half the power absorbed by the combination less the known losses in 
the armatures, magnets, and external connexions of the two machines; column XIV. 
is the total mechanical power given to the generator, being the sum of the powers 
given in columns XII. and XIII. 
Table II. 
■ 
1 
I. 
Per cent. 
IT. 
Per cent. 
III. 
Per cent. 
IV. 
Per cent. 
V. 
Per cent. 
VI. 
Per cent. 
1 
0-25 
18-23 
12-52 
69-0 
71-44 
40-44 
2 
0-65 
8-30 
717 
83-88 
69-9 
58-63 
3 
1-235 
4-27 
4-27 
90-22 
89-68 
79-9 
4 
1-52 
3-53 
2-66 
92-29 
92-78 
85-63 
5 
1-84 
2-94 
2-415 
92-81 
93-70 
86-51 
6 
311 
1-70 
1-94 
93-25 
93-79 
87-45 
7 
3-17 
1-66 
1-94 
93-23 
93-37 
87-05 
8 
3-08 
1-67 
1-98 
93-27 
93-99 
87-26 
9 
3-525 
1-51 
1-59 
93-37 
94-02 
87-49 
10 
4-47 
1-20 
1-00 
93-39 
93-62 
87-43 
11 
0-31 
3-53 
2-66 
92-29 
92-78 
85-63 
In Table II. the percentage losses in the armature and magnets of the generator 
are given, as also the sum of all other losses as obtained from column XIII. in the 
foregoing table ; also the percentage efficiency of the generator, of the motor, and of 
the double conversion. Column I. is the percentage loss in the generator armature; 
column II. is the percentage loss in the generator magnets; column III. is the per¬ 
centage sum of all other losses in the generator ; column IV. is the percentage 
efficiency of the generator; column V. is the percentage efficiency of the motor ; 
column VI. is the percentage efficiency of the double conversion. 
In this series of experiments in all cases, from Nos. 1 to 10 inclusive, the brushes, 
both of the generator and motor, were set at the non-sparking point; but in No. 11 
no lead was given to the brushes of the generator, and, consequently, there was 
violent sparking throughout the duration of the experiment. 
In No. 12 the magnets were separately excited with a current giving 113*5 volts 
