Tesla Reciprocating Dynamo

There have been, so far as we remember, only three attempts to apply simple reciprocating motion, instead of rotary movement round an axis, to the armature of a dynamo. The first of these was the "thunder-pump," a magneto device used for ringing-up in the early days of telegraphy. Perhaps this instrument ought not to be classed as a dynamo, but it was a practical success in its day. As much cannot be said for the Edison tuning-fork dynamo. Electrically, this second attempt was reasonable, but it was mechanically impossible and absurd. The third reciprocating dynamo is that of Nikola Tesla. This was first shown in a lecture delivered by the inventor before the Chicago Congress, and is illustrated and described elsewhere in our present issue. The account, for which we are indebted to the Electrical Engineer of New York does not allude to the principal object in view in designing this machine. We understand, from the reports of the lecture, that high frequency was Mr. Tesla's aim. In the Electrical Engineer of New York, for August 30, 1893, we find that a mass of about 20lb. was kept in vibration with a stroke of in. at a frequency of about 80 per second, "but by shortening the stroke the weight could be vibrated many hundred times, and has been in other experiments." This result seems hardly sufficient to justify so, complete a departure from ordinary practice, but on looking up the subject we found some more figures in the Electrical World of New York, for September 2, 1893. "The piston is operated by compressed air at 60lb. per square inch. The compression reaches as much as 16 tons. The number of oscillations used at the lecture was from 50 to 90 per second, although from 5,000 to 10,000 per second have been obtained, and as many more as desirable "!