22 2 POPULAR SCIENCE MONTHLY. 



metallic springs of exquisite delicacy. At each perforation the 

 springs touch and the current takes its way through the wire. 

 At the receiving station the delay involved in the arousal and 

 action of electro-magnets is abolished. The current instant by in- 

 stant writes its message on a moving ribbon of paper sensitized so 

 as to change color under an electric flow. ' This instance is typical 

 of what ingenuity can do when electricity is added to its armory. 

 A task is divided between an operator and an automatic machine 

 in such wise that intelligence is allotted only that part for which 

 intelligence is required, while for the remaining part the utmost 

 speed of electrical and chemical action is invoked a pace which 

 in this particular case sixtyfold outstrips the most dexterous 

 manipulation. 



Another means by which inventors have expedited telegraphy 

 has been by transmitting several messages simultaneously over a 

 single wire. Of these multiplex systems certain are synchronous 

 in principle and seem to have suggested to Prof. Elisha Gray his 

 telautograph, an instrument that imitates exactly the motion of a 

 pencil, in say Boston, by the motion of another, in say Baltimore, 

 reproducing with equal facility either handwriting or outline 

 drawing. To understand the principle involved, let us glance at 

 an everyday application of electricity in keeping scores of clock 

 pendulums, no matter how far apart, in perfect step. If two pen- 

 dulums at right angles to each other are attached to a moving 

 pencil their motions may be communicated to a distance by two 

 currents which actuate two pendulums in control of a second and 

 copying pencil. The electric clock at which we have just been 

 looking can, if we please, be sealed in a glazed box, secure from 

 dust and dampness. Here opens a fresh path to the inventor who 

 wishes to avoid the resistance or leakage entailed when a rod 

 moves through a slot or a stuffing box. It is often of cardinal 

 importance that a bit of metal at rest should throb with a pulse 

 strong enough to do severe drudgery or tell a tale which other- 

 wise would go untold. If an engineer wishes to know how much 

 heat wastes itself through the walls of a steam cylinder, his ques- 

 tion is answered through a motionless wire attached to a delicate 

 metallic thermometer buried in the cylinder's mass. In experi- 

 menting with new alloys the same method informs the chemist of 

 changes of temperature at the core of his crucible, changes often 

 abrupt and transient and at times denoting qualities he seeks to 

 detain or reproduce. In a very different domain of exploration 

 the engineer uses the telephone to expose perilous defects in metal 

 beams. 



As we prove when we unhook a telephone, or lift an incan- 

 descent lamp, electricity readily traverses a flexible wire : this un- 

 bars a fresh resource to invention. To-day rock drills, coal cut- 



