results were of much utility in their bearing on the
working of submarine cables, and it is not too much to affirm that it
was to Sir William Thomson's counsel that the success of the Atlantic
Cable is in great part due. His mirror galvanometer was the first
instrument that could be applied with anything like satisfactory results
to submarine telegraphy. More recently, however, he has invented and
patented another instrument, called the "syphon recorder," which was
exhibited publicly for the first time at the opening of the British
India Submarine Telegraph. The special feature of the "syphon recorder"
is a minute capillary syphon, which, while it continually discharges ink
against a moving paper, is by means of a delicate electro-magnetic
arrangement caused to move from side to side _according to the electric
pulses passed through the cable_, and from the record thus obtained of
these motions the message is deciphered. From trials lately made on the
Falmouth, Gibraltar, and Malta lines, it has been ascertained that 25
words per minute can be registered through a cable 800 miles long. It is
also a recommendation to the "syphon recorder" that it can be worked by
very low battery power, and therefore tends to the preservation of the
cable. Among Sir William's other inventions we may specially mention an
electrometer, which has now assumed a very complete form. His
divided-ring electrometer admitted of accurate measurements, in skilled
hands, of fractions of a Daniell's cell; his portable electrometer
admits of readings from 10 or 20 cells upwards; but his new reflecting
electrometer gives as much as 100 divisions on the scale for one single
cell of the battery. In Mr. Varley's patent of 1860, he describes a
method which he employed to make the one plate charge itself, and on
this principle he constructed a large electrical machine, which he
exhibited at a soiree of the Royal Society of 1869-70. This machine has
been adopted by Sir William Thomson for maintaining the charge in his
electrometer. The new electrometer is really a combination of three
inventions--of Sir William Thomson's portable electrometer to indicate
whether or no the instrument is sufficiently charged; of the replenisher
by Mr. Varley for charging or discharging; and of the quadrant
electrometer for reading off the minute tensions measured. The
instrument is in its present form so practically useful that it has been
largely used in connection with telegrap