One is asked a great many questions, as, “How many empires do you take?” “Why don't your clothes catch fire?” and, too, I am frequently accused of having secret wires and plates on the floor, so now I carry a light board platform upon which I stand while working. The audience is asked to figure the voltage of the sparks from the fact that 20,000 volts is the pressure required to force a spark across a one inch air space and between needle points. But they are in the main interested, I think, because a woman dares.

Popular Electricity - March, 1910

Faking High Voltage Sparks

“All is not gold that glitters” - nor is all high voltage that gives a fierce and crackling spark. Last fall a London music-hall performer who claimed to give the marvelous exhibition of coolly taking a shock of 30,000 volts, astonished large audiences night after night. One man who thought that this self-styled “medical electrician” had discovered wonderful secrets paid a fancy price to become his pupil, only to learn that the pretended expert was a faker. The suit through which the deceiver was ordered to return the tuition money showed that in his public performance he used a type of high frequency apparatus built for college and hospital work, which gave a harmless spark. Then to get his impressive effects, he cleverly used fireworks paper which crackled and flared in addition to this spark.

Electrical World - April 24, 1897

Insulation for High Frequency Currents.

To the Editor of The Electrical World:

Sir: - The question of insulating high-frequency currents has been one of so much interest that I am impelled to give my own experience in the matter.

Believing, with many, that oil was not a practical insulator for office use, I at first tried the various forms well known in induction coil work. All, however, proved to be entirely useless, as great loss of current was apparent from the very beginning, and a few hours' use only served to break the insulation down completely. My attention was then called to pure paraffine, which we applied hot and in a vacuum. This served admirably for a time, and I was inclined to believe my efforts had been crowned with success. In two days of constant use, however, the discharge commenced to be more flashy. This continued until the third day, when the insulation gave way entirely. This experiment was several times repeated with no better results. As a last resort I then turned to oil. After carefully testing many samples and winding my coil with special reference to that form of insulation, I then mounted the high-frequency coil, which has been in use ever since. After eleven months of almost constant use in the manufacture of Crookes tubes, the length and character of the discharge or consumption of current have not materially changed. During that time the oil has not been renewed, and there is not, apparently, the slightest indication of gumming.

If my experience has been different from that of others in this particular I shall be pleased to present substantial evidence of the truth of the condition above mentioned.

In view of this fact, I am forced to believe that oil is the only practical insulation for this work.

E. Cate.

Boston. Mass.

Electrical World - Sept. 9, 1909

High-Frequency Oscillations.

At a meeting of the Wireless Institute, held on Sept. 1 at the Engineering Societies Building, New York, Mr. Harry Shoemaker presented a paper entitled, “The Production of High-Frequency Oscillations.” The author outlined the characteristics of damped and sustained oscillations and stated that, while the latter are used for wireless telephony, the former are employed almost exclusively for wireless telegraphy. Damped oscillations are produced in practice by the discharge of a condenser across a spark-gap through an inductive circuit. The period of the oscillation depends upon the product of the capacity of the condenser and the inductance of the circuit. The antenna may be directly connected to the exciting circuit or it may be inductively associated therewith. In practice use is frequently made of a combination of the two connections. The ratio of the mutual inductance to the square root of the two self-inductances is known as the coupling coefficient; it may be as low as 0.1, but is usually about 0.2. Best results are obtained when the natural period of the antenna circuit is the same as that of the exciting circuit. Energy stored in a condenser during each cycle has a value proportional to the product of the capacity and the square of the voltage; the power utilized varies directly with the number of cycles per second. It is found that a 0.0075-mf condenser requires 1 kw when operated at a frequency of 60 cycles and an e.m.f. of 20,000 volts. Five kilowatts are used when the frequency is 120, the capacity 0.03 mf and the e.m.f. 28,000 volts.

In a conversational discussion following the reading of his paper, the author remarked that the best form of antenna is a straight wire mounted in the vertical plane. Energy for the condenser in the exciting circuit is obtained from the secondary of a transformer constructed with a large amount of magnetic leakage so that the current remains practically constant from full load to direct short circuits. On account of the leading condenser current the actual, secondary e.m.f. is much greater than the value found by multiplying the primary e.m.f by the ratio of turns. Moreover, the e.m.f. per turn is not uniform throughout the secondary coil, being greater at the end-turns.