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142 
THE QUANTUM 
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L^j = the number of magnetic tubes threading through 
circuit No. 1 due to its own current. 
L z i 2 — the corresponding number of tubes for circuit No. 2. 
M 12 i! = the number of tubes threading through circuit No. 2 
due to the current in circuit No. 1. 
M 12 * a = the number of tubes threading through circuit No. 1 
due to the current in circuit No. 2. 
The magnetic tubes may be grouped together in various different 
ways which may be illustrated more clearly by a purely dia 
grammatic scheme such as that illustrated in Fig. 22. 
Fig. 22.—Magnetic Tubes for two Current Circuits. 
The two current circuits I and II are shown in black. In this case 
N x , the number of tubes linked only with circuit I is 2, 
N 2 , the number of tubes linked only with circuit II is 3, 
N 12 , the number of tubes linked with both circuits is 2, 
n x , the total number of tubes linked with circuit I is 4, 
n 2 , the total number of tubes linked with circuit II is 5, 
whilst the total number of tubes in the diagram is 7. 
The total number of tubes linked with the first circuit is 
rij = Li*! + M 12 i a . . (4 in Fig. 22) 
The total number of tubes linked with the second circuit is 
n 2 = L 2 « 2 + Mjaij . . (5 in Fig. 22) 
Again, the number, N l5 of tubes linked only with circuit No. i 
is the difference between the number of tubes passing through 
circuit No. 1 due to its own current, and the number passing 
through circuit No. 2 due to the current in circuit No. i, i.e. 
N x = L^'i — M 12 i! . . (2 in Fig. 22) 
In the same way the number of tubes linked only with circuit 
No. 2 is 
N a = L 2 i' a . . (3 in Fig. 22)