This scheme requires about as small current as is likely to be practical, perhaps, especially when the spark is in a suitable degree of vacuum, and, of course, the incoming radio signals require correspondingly small amplification.
FILAMENT LAMP:
The direct source of light which in the author’s laboratory has produced the most perfect photographic effects, i. e., photographs absolutely without lines, consists of a lamp about an inch in diameter and two inches long, fitted with a standard screw base. The tube contains a .6 mil filament with a small single turn coil in a hydrogen atmosphere.
The coil is offset until it almost touches the glass wall. Such location of the coiled filament permits the effective placing of a minute aperture in very close relation to the filament; whereas an aperture on the outside of a bulb with the light source in the centre of the bulb acts like a pin-hole camera, and sharpness of image is practically impossible (unless a lens is used).
The lamp described above will respond to fluctuations in current well above a thousand times per second, but requires voltages about four times normal. It was made for the author by courtesy of the General Electric Company, under the direction of Mr. L. C. Porter, of Harrison, N. J.
CORONA LAMP:
But the lamp that really elicits the author’s unqualified admiration is the corona glow lamp made for the author by Professor D. McFarlan Moore. It consists of a small glass bulb containing a neat-fitting metallic cylinder, one terminal of an attached circuit. Inside and concentric with the cylinder is a second cylindrical capsule made of a solid rod drilled to a predetermined depth.
The electron stream from the outside cylinder to the capsule naturally takes the long path, and as the longest path is down into the capsule, the result is that the small central opening of the capsule glows with great intensity while the other parts of the lamp remain dark. This lamp, Professor Moore advises, has a light and dark frequency of a million per second.
