MR 0. V. BOYS ON THE RADIO-MICROMETER. 
1G7 
n. 
Best 1. 
Ew^. 
1 
4-621 
9-202 X 
2 
2-SlI 
7-565 
3 
2-207 
6-423 
4 
1-905 
5-580 
5 
1-724 
4-933 
Best a. 
I 
> 2-0075. 
Thus, it appears that one turn is better than any other number, provided that the 
circuit may have sufficient length, and, of course, that the magnetic field is sufficiently 
extended. This result is really self-evident, for, whatever may be the efficacy of a 
circuit of say two turns of the best length, one of one turn of twice the length must 
be better, as in this case the value of the enclosed magnetic field will be the same, 
while the resistance and the weight will each be less, and, further, the circuit of twice 
the length will not have the best length for one of one turn only. 
If the length of the circuit is limited to 1 cm., then two turns are better than one 
or three. The series of figures found on this supposition are not of sufficient impor¬ 
tance to be worth giving. 
It is interesting, however, to notice how slowly the efficacy changes when the 
length of the circuit is not the best. The following figures show this :— 
1 . 
E 
Wt‘ 
3 
oc 
to 
X 
10“^ 
3-5 
9-036 
55 
4 
9-152 
55 
4-5 
9-200 
55 
4-621 
9-202 
55 
5 
9-190 
5 5 
max. 
Thus, it is not a matter of much consequence whether the circuit is very near the 
best length or not. 
If it is desired to find the numerical value of the resistance or the weight of the 
wire part of the circuit when it is of the best length and sectional area, the following- 
expressions, which have been obtained by substituting in those for r and lo the best 
values found for a and I, may be used to save time:— 
bestr=C + .(4). 
best« = w(l + 2 p 
(5). 
