198 
Proceedings of Royal Society of Edinhurgli. 
[SESS. 
down to 15, and messages could still easily be sent, the resistance 
of the primary being 24 ohms, and the secondary no less than 
260 ohms. If the circuit had been of good iron, with soldered 
joints, and well earthed, the resistance should have been only 
60 ohms. The induced current therefore generated in the secondary 
would therefore be in the ratio of 480 to 210, or with this great 
resistance, allowing for the resistance in the two telephones in 
multiple, we got practically only half the current we would have 
got if the line had been a permanent in place of a temporary one. 
A trial was made of the parallel wire system, and with 20 cells 
the sound was not heard, and with 100 cells it was heard by me as 
a mere scratch in comparison with the sound with the coil system 
with 15 cells. A trial was made with a phonopore, and the coils 
worked with 10 cells with perfect ease, and a message was received 
with only 5 cells. Speech by means of Deckert’s transmitter was 
just possible, but it is believed that if the hearing circuit had been 
of less resistance it would have been easy to hear. 
It is difficult to understand how this system of coils, in opposi- 
tion to the parallel wire system, has not been recognised as the best. 
For, assume that with the arrangements we had, we heard equally 
well with 100 cells by both systems, both having the same base 
(200 yards), then by simply doubling the number of turns of wire, 
and using thick wire of low resistance, the effect would have been 
practically doubled, whereas, by the parallel wire system, there is 
nothing for it but to increase the battery power, which, for ^practical 
working^ becomes an impossibility. The difficulty of the current is 
thus removed by using a number of turns of wire. There is shown 
on the following diagram (fig. 3) the result of simply increasing 
the diameter with a given length of wire, keeping current and 
resistance the same. It shows that the larger the diameter the 
better ; in fact, with a given length of wire, a straight one is the 
best. But this is not practicable ; what is wanted is to get induction 
at a great distance from a certain given base with a small battery 
power, and the laboratory experiments and the trials in the field 
show that the way to overcome the difficulty of the current is by 
using a number of turns of wire The secret of success is to 
apportion the resistance of primary and secondary and the number 
of turns on each to a practical battery power. 
Coil System. — (1) At 850 yards from centre to centre of coils 
