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apparatus was untouched since the previous trials. results of these trials are summarised in Appendix 1, and they were considered at a meeting of the technical com- mittee on the 10th April. The Committee agreed unani- mously that the number of false calls registered by the G.P.O. instrument conclusively showed that the 15 seconds dash was not a suitable signal for this purpose.
It was also agreed that the two other instruments should be tested on a voyage through the tropics before any final conclusions were reached.
7. Through the courtesy of the Ellerman Lines, who lent their Steamship "City of Harvard for the purpose, further trials were carried out by operators lent by the Wireless Companies under the supervision of an Admiralty officer on a voyage out to Bombay and Karachi and back, beginning on 16th May and ending 13th August The results of these trials are summarised in Appendix 2. The operators again had no special training and the apparatus was as turned over from the " Rathlin.
8. The results of the various tests were discussed at a conference held at the Admiralty on the 29th October, and the following points were raised in connection, particularly with the Foreign trial.
(a) Continuous adjustment of the devices was necessary
during the first 24 hours.
(b) The longest time that the devices were left without being adjusted, while working successfully, was-
For the Marconi Instrument, 50 hours.
For the Radio Communication Company's
Instrument, 40 hours.
(c) A question arose as to why the
improved, whereas the Emergency
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results
results With
deteriorated, on the homeward voyage.
regard to the first, it was explained that the operators understood the instruments better as time went on, and they were run for shorter periods without re-adjustment. With regard to the Emergency results, these were accounted for by encountering bad emergency sets, at longer ranges, on the homeward voyage.
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(d) False calls were less on the homeward voyage, on account of more experience in adjustment of the devices being gained by the operators. False calls may really be considered negligible.
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(e) Most faults were due to batteries. There are no possibilities of reversed polarity in regard to the charging of H.T. batteries.
(f) It was considered that no purpose would be served by discussing details of the devices, but that they could probably be much improved.
(g) It was considered that an operator would recognise the auto-call dashes with as much, or greater, ease than the ordinary S.O.S. signals.
even
(h) It was noticed that atmospherics caused failures.
as was to be expected.
Atmospherics had the effect of closing the break space thus, in the case of the Radio set, throwing it back to the original position or in the case of the Marconi set jamming the two relays. Nearly all the failures were due to atmospherics.
(i) The trials are considered to show that automatic sending is very desirable, as in practice it was found that the length of the dashes as sent varied from 2 to 54 seconds, while the spaces varied from to 2 seconds. The Committee considered that if a simple and reliable instrument can be designed for this purpose, the question of making its carriage compulsory might be considered by the Board of Trade.
In this connection, although not mentioned at the con- ference, it is to be noted that some ships have no second hands on their clocks.
(1) It was clear that apparatus of this kind can only re- spond to a call sent out within certain reasonable limits of accuracy, i.c., it cannot, like an operator, make out that someone is trying to send the signal but failing to do it properly owing to in- accurate timing or faulty apparatus.
(k) It was considered, in regard to the general working of the devices, that the limit of effective calls possible is not less than 90 per cent. for a per- fected device.
9. The following standard test for auto-call devices was agreed to generally :-
(i) The devices shall normally be operated by a series of three dashes, each of four seconds duration, separated by a space of one second.
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