Nikola Tesla Books
Books written by or about Nikola Tesla
XXVII. This photograph shows an incandescent lamp 16 c.p., 100 V connected with one of its terminals to the top or free end of the extra coil, the lower end of the latter being connected to the ground plate. The carbon filament is brought to incandescence by the currents transmitted from the ground plate and the rarefied gas is also glowing as evident from the photograph. It is instructive to note the great actinic power of the glowing gas which, though appearing to the eye of feeble luminosity as compared with the lamp filament, nevertheless impresses the plate at least as strongly, if not more so, than the incandescent filament.
In many experiments made a few years ago I observed this and also that certain gases are particularly adapted to impress the plate. This fact, again observed, impresses me more and more with the value of powerfully excited vacuum tubes for purposes of photography. Ultimately, by perfecting the apparatus and selecting properly the gas in the tube, we must make the photographer independent of sunlight and enable him to repeat his operations under exactly the same conditions, which is almost indispensable in order to attain the best results. Such tubes will, however, enable him to regulate the conditions and adjust the light effects at will. Such a facility would offer a very great advantage to the artist as with the sunlight, particularly in large cities where the air is not very pure, he has to rely much on chance and where it is almost impossible for him to perform two successive operations under the same conditions or to adjust beforehand the light effects. The photograph described shows also the high actinic power of streamers when they are of a bluish or violet color as frequently, which is the case in this instance. The red streamers are comparatively very slow in their action, but it should be stated that apart from the color the action on the plate is determined much by the power or intensity of the streamers. Thus with the powerful apparatus which I have perfected here the actinic rays are much more powerful than with the New York apparatus. In the experiment illustrated the results would have been the same if both of the terminals of the lamp would have been connected to the free end of the "extra coil" instead of only one, as illustrated in the diagram, which is added for the purpose of showing more clearly how the connections in this case were made.
Now, as to the other particulars of the experiment, the capacity in the primary or exciting circuit was 3 tanks on each side or 1 1/2 tanks total, that is 54 bottles or 54 x 0.0009 = 0.0486 mfd. As to inductance of the exciting circuit there was the primary turn with closed secondary = 41,000 cm. and 5 3/4 turns of regulating coil, including connections, making an inductance, according to the table, of 17,684 cm, that is, the
The explanation to Photograph XXII concerning the transmission of power from the excited primary circuit to the "extra coil" via the earth is similar to that he gave in 1893(6). The experiment to which the photograph refers was made with the aim of estimating the power of the oscillator from the thermal effect of the HF current. What Tesla calls the "total energy set in movement" would correspond to the total energy transferred to condenser in the secondary (i.e. the power) if an energy of !${1 \over 2}!$ CV2 is transferred in each half-cycle. It can be shown that the active power dissipated in the circuit is much less than this and is inversely proportional to the Q-factor of the oscillating circuit.
