If long circuits were worked direct with ordinary instruments, high battery power would be required in order to send sufficient Single current to actuate the apparatus.
The relay was employed to actuate through a local battery B2 an ordinary Morse printing telegraphic instrument M.
The different kinds of motive power used to actuate cranes - manual, steam, hydraulic, electric - give a further classification.
At regular intervals a rotating arm on the distributor connects the five keys of each keyboard to line, thus passing the signals to the distant station, where they pass through the distributor and certain relays which repeat the currents corresponding to the depressed keys and actuate electromagnets in the receivers.
The relay itself served to actuate a Morse printing telegraph by means of a local battery.
The currents actuate a ratchet-wheel mechanism at the receiving station, whereby the hand on a small dial is moved on letter by letter.
Owing to the difficulty of maintaining perfect balance on duplexed cables, curb sending is not now used, but the signals are transmitted by means of an apparatus similar to the Wheatstone automatic transmitter used on land lines and differing from the latter only in regard to the alphabet employed; the signals from the transmitter actuate a relay having heavy armatures which in turn transmit the signals to the cable; this arrangement gives very firm signals, a point of great importance for good working.
The same infatuated passion for mining speculation which had characterized the Spanish settlers in South America now began to actuate the Portuguese; labourers and capital were drained off to the mining districts, and Brazil, which had hitherto in great measure supplied Europe with sugar, sank before the competition of the English and French.
There are also two vertical racks, one at each end of the casing, in connexion with - the two springs, and these actuate pinions on the axle of the drum and cause it to revolve as the springs extend.
The slips are passed through an ordinary Wheatstone transmitter and actuate Wheatstone receiving apparatus which in turn controls a " Creed receiving perforator."