Page:Heroes of the telegraph (IA cu31924031222494).djvu/109

 writing-tablet. The only avenue of escape for it is by the fine glass siphon, and through this it rushes accordingly and discharges itself in a rain upon the paper. The natural repulsion between its like electrified particles causes the shower to issue in spray. As the paper moves over the pulleys a delicate hair line is marked, straight when the siphon is stationary, but curved when the siphon is pulled from side to side by the oscillations of the signal coil.

It is to the mouse-mill that me must look both for the electricity which is used to electrify the ink and for the motive power which drives the paper. This unique and interesting little motor owes its somewhat epigrammatic title to the resemblance of the drum to one of those sparred wheels turned by white mice, and to the amusing fact of its capacity for performing work having been originally computed in terms of a 'mouse-power.' The mill is turned by a stream of electricity flowing from the battery above described, and is, in fact, an electro-magnetic engine worked by the current.

The alphabet of signals employed is the 'Morse code,' so generally in vogue throughout the world. In the Morse code the letters of the alphabet are represented by combinations of two distinct elementary signals, technically called 'dots' and 'dashes,' from the fact that the Morse recorder actually marks the message in long and short lines, or dots and dashes. In the siphon recorder script dots and dashes are represented by curves of opposite flexure. The condensers are merely used to sharpen the action of the current, and render the signals more concise and distinct on long cables. On short cables, say under three hundred miles long, they are rarely, if ever, used.

The speed of signalling by the siphon recorder is of course regulated by the length of cable through