1872.] Electricity. 127 
M. W. Beetz has lately made several determinations of the ele@tro-motive 
force of various hydro-electric elements, employing a compensating battery 
and a system which seems capable of great exactitude. A Bunsen’s element 
he considers to give an electro-motive force = 1-799, a Grove’s element = 1°684, 
and a Leclanché = 1°167 times that of a Daniell’s standard cell. 
A printing telegraph for private wires, patented in America about a year ago 
by Messrs. Pope and Edison, has lately been brought under the notice of the 
English public. It is well adapted for private wires and for railway telegraphs, 
being simple and durable in construction, and capable of being understood and 
operated without difficulty by persons having no special knowledge of 
telegraphy. The instrument operates upon what is known as the ‘open cir- 
cuit” principle, each station transmitting with its own battery—the line at the 
receiving station being connected directly through the relay to the earth, 
without the intervention of a second battery. The printing apparatus is 
placed upon a circular iron base in the centre of the table. In front of it is 
placed a dial, containing the letters of the alphabet, arranged in a circle, and 
provided with an index or pointer, mounted upon a horizontal shaft. This 
shaft also carries a type-wheel and a scape-wheel, with racket-shaped teeth, 
corresponding in number to the characters upon the type-wheel and dial. An 
electro-magnet beneath the base is provided with an armature, attached toa 
vibrating lever, the latter armed with pawls or clicks, so arranged in relation to 
the scape-wheel that every time the electro-magnet attracts its armature the 
wheel is made to revolve a distance of one tooth, and the type-wheel and index 
upon the same shaft a distance of one letter. At the extreme right of the 
circular base, and partly beneath it, is placed a second eleétro-magnet, whose 
armature lever passes in a horizontal direction below the type-wheel. Diredly 
underneath the type-wheel an india-rubber pad is fixed upon the lever, by 
means of which an impression of the letter opposite it upon the type-wheel 
may be taken, The lever is also provided with a simple mechanical device for 
moving the paper forward the proper distance, as each successive character is 
imprinted upon it. The type-wheel is provided with a suitable inking roller. 
It will thus be understood that the printing mechanism is operated by two dis- 
tind electro-magnets, one of which is so arranged that its successive pulsations 
may be made to advance the index step by step to any required letter, while 
the other forces the strip of paper against the inked type upon the wheel, after 
it has been moved to the proper position by the first magnet. These two 
electro-magnets are placed in the circuit of a local battery, which is brought 
into action by a relay placed in the main line circuit, as in the ordinary Morse 
instrument, and is the same in principle, with the addition of a device termed 
the ‘ polarised switch,” which consists of a permanently magnetised steel bar 
pivotted between the poles of the relay magnet, the polarity of which depends 
upon the direction of the electrical current in the main circuit. The polarised 
switch determines the direction of the local current, causing it to pass through 
the magnet for moving the type-wheel, or through the impression magnet, as 
may be required. Two lever finger-keys are connected to the poles of the 
main battery in such a manner that, by depressing the right-hand key, the 
positive pole of the battery is connected, through the relay magnet to the line, 
and the negative to the ground, while the left-hand key, on the contrary, sends 
a negative current through the relay and line inthe same manner. By depres- 
sing the right-hand key a sufficient number of times in rapid succession, 
a series of positive currents is sent through the relays at both ends of the line, 
which series is repeated upon the local circuits of both instruments. The 
positive currents defle@ the polarised switches to the left, so that the local 
current is directed into the type-wheel magnet. The index and type-wheel of 
both instruments, therefore, advance one letter every time the key is depressed, 
and they may thus be readily brought to any desired letter. When this has 
been done, the left-hand key is depressed, which sends a negative current, 
reversing the polarised switch, and throwing the local circuit through the 
printing magnet, producing the impression of the letter upon the strip of paper. 
The apparatus, it will be seen, is entirely automatic, while it is also very 
