s obtained in the
following manner. The receiving cylinder travels at a speed slightly in
excess of the transmitting cylinder, and as its revolution is finished
first is prevented from revolving by a check, and when in this position the
receiving apparatus is thrown out of circuit and an electro-magnet which
operates the check is switched in. When the transmitting cylinder has
completed its revolution (about 1/100th of a second later) the transmitting
apparatus, by means of a special arrangement, is thrown out of circuit for
a period, just long enough for a powerful current to be sent through the
line. This current actuates the electro-magnet. The check is withdrawn and
the receiving cylinder commences a fresh revolution in perfect synchronism
with the transmitting cylinder. As soon as the check is withdrawn the
receiving apparatus is again placed in circuit until another revolution is
completed. As the receiver cannot stop and start abruptly at the end of
each revolution a spring clutch is inserted between the driving motor and
the machine. {72}

Although a method of synchronising similar to this may later on be devised
for wireless photography, the writer, from the result of his own
experiments, is led to believe that results good enough for all practical
purposes can be obtained by fitting a synchronising device whereby the two
machines are started work at the same instant, and relying upon the perfect
regulation of the speed of the motors for correct working.

The method of isochronism must, however, be nearly perfect in its action,
as it is easy to see that with only a very slight difference in the speed
of either machine this error will, when multiplied by 40 or 50 revolutions,
completely destroy the received picture for practical purposes.

From what has been written in this and in the preceding chapters it will be
evident that the successful solution of transmitting photographs by
wireless methods will necessitate the use of a great many pieces of
apparatus all requiring delicate adjustment, and depending largely upon
each other for efficient working. As previously stated, there is at present
no real system of wireless photography, the whole science being in a purely
experimental stage, but already Professor Korn has succeeded in
transmitting photographs between Berlin and Paris, a distance of over 700
miles. If such a distance could be worked over successfully, there is no
reason to doubt that before long {73}