if any) sparking; but, as
most wireless workers know, anything in the nature of a spark occurring in
the neighbourhood of a detector (this, of course, only applies when the
receiving apparatus is placed in close proximity to the transmitter) is
liable to destroy the adjustment.

In transmitting over ordinary conductors where the initial voltage is
fairly high and the self-induction of the circuit very great, the use of
the condenser will be found to be absolutely essential. It has also been
noted that the angle which the stylus presents to the drum has a marked
effect upon the sparking, an angle of about 60deg being found to give very
good results.

If the size of the single line print used is 5 inches by 4 inches, and a
screen having 50 lines {25} to the inch is used for preparing it, then the
stylus will have to make 250 contacts during one revolution of the drum.
Assuming the drum to make one revolution in three seconds, then the time
taken to transmit the complete photograph can be found from the equation T
= w x t x s, where w is the width of the print, t the travel of the stylus
during one revolution of the drum, and s the time required for one
revolution of the drum. In the present instance this will be T = 4 x 90 x 3
= 1080 seconds = 18 minutes. The number of contacts made by the stylus per
minute is 5000, and in working at this speed the first difficulty is
encountered in the use of the two relays. The relay R is lightly built, and
capable of working at a fairly high speed, but R' is a heavier pattern, and
consequently works at a slightly lower rate. This relay must necessarily be
heavier, as more substantial contacts are needed in order to pass the heavy
current taken by the spark-coil.

Relays sensitive and accurate enough to work at this speed will in all
probability be beyond the reach of the majority of workers, but there are
several types of relays on the market very reasonable in price that will
answer very well for experimental work, although the speed of working will
no doubt be slower.

For the best results the duration of the wave-trains sent out should be of
the same duration as {26} the contact made by R, and therefore equal to the
time taken by the stylus to trace over a conducting strip; but if the
duration of the contact made by R is t, then that made by R' and
consequently the duration of the groups of wave-trains would be t - v where
v equals the extra time required by R' to complete its lo