Fig 32 33 ­ ELECTRO DYNAMIC,INDUCTION COIL INDUCTION LAMP

In Fig. 32 a wide tube T was sealed to a smaller W-shaped tube U, of phosphorescent glass. In the tube T was
placed a coil C of aluminium wire, the ends of which were provided with small spheres t and t1 of aluminium, and
reached into the U tube. The tube T was slipped into a socket containing a primary coil through which usually the
discharges of Leyden jars were directed, and the rarefied gas in the small 17 tube was excited to strong luminosity
by the high-tension currents induced in the coil C. When Leyden jar discharges were used to induce currents in the
coil C, it was found necessary to pack the tube T tightly with insulating powder, as a discharge would occur
frequently between the turns of the coil, especially when the primary was thick and the air gap, through which the
jars discharged, large, and no little trouble was experienced in this way.
In Fig. 33 is illustrated another form of the bulb constructed. In this case a tube T is sealed to a globe L. The tube
contains a coil C, the ends of which pass through two small glass tubes t and t1, which are sealed to the tube T. Two
refractory buttons m and mx are mounted on lamp filaments which are fastened to the ends of the wires passing
through the glass tubes t and t1. Generally in bulbs made on this plan the globe L communicated with the tube T.
For this purpose the ends of the small tubes t and t1 were just a trifle heated in the burner, merely to hold the wires,
but not to interfere with the communication. The tube T, with the small tubes, wires through the same, and the
refractory buttons m and m1, was first prepared, and then sealed to globe L, whereupon the coil C was slipped in
and the connections made to its ends. The tube was then packed with insulating powder, jamming the latter as tight
as possible up to very nearly the end, then it was closed and only a small hole left through which the remainder of
the powder was introduced, and finally the end of the tube was closed. Usually in bulbs constructed as shown in
Fig. 33 an aluminium tube a was fastened to the upper end s of each of the tubes t and t1, in order to protect that
end against the heat. The buttons m and m1 could be brought to any degree of incandescence by passing the dis-
charges of Leyden jars around the coil C. In such bulbs with two buttons a very curious effect is produced by the
formation of the shadows of each of the two buttons.
Another line of experiment, which has been assiduously followed, was to induce by electro-dynamic induction a
current or luminous discharge in an exhausted tube or bulb. This matter has received such able treatment at the
hands of Prof. J. J. Thomson that I could add but little to what he has made known, even had I made it the special
subject of this lecture. Still, since experiences in this line have gradually led me to the present views and results, a
few words must be devoted here to this subject.
It has occurred, no doubt, to many that as a vacuum tube is made longer the electromotive force per unit length of
the tube, necessary to pass a luminous discharge through the latter, gets continually smaller; therefore, if the ex-
hausted tube be made long enough, even with low frequencies a luminous discharge could be induced in such a
tube closed upon itself. Such a tube might be placed around a hall or on a ceiling, and at once a simple appliance
capable of giving considerable light would be obtained. But this would be an appliance hard to manufacture and
extremely unmanageable. It would not do to make the tube up of small lengths, because there would be with
ordinary frequencies considerable loss in the coatings, and besides, if coatings were used, it would be better to
supply the current directly to the tube by connecting the coatings to a transformer. But even if all objections of such
nature were removed, still, with low frequencies the light conversion itself would be inefficient, as I have before
stated. In using extremely high frequencies the length of the secondary--in other words, the size of the vessel--can
be reduced as far as desired, and the efficiency of the light conversion is increased, provided that means are
invented for efficiently obtaining such high frequencies. Thus one is led, from theoretical and practical
considerations, to the use of high frequencies, and this means high electromotive forces and small currents in the
primary. When he works with condenser charges--and they are the only means up to the present known for
reaching these extreme frequencies--he gets to electromotive forces of several thousands of volts per turn of the
primary. He cannot multiply the electro-dynamic inductive effect by taking more turns in the primary, for ho ar-
rives at the conclusion that the best way is to work with one single turn--though he must sometimes depart from
this rule--and he must get along with whatever inductive effect he can obtain with one turn. But before he has long
experimented with the extreme frequencies required to set up in a small bulb an electromotive force of several
thousands of volts he realizes the great importance of electrostatic effects, and these effects grow relatively to the
electro-dynamic in significance as the frequency is increased.
Now, if anything is desirable in this case, it is to increase the frequency, and this would make it still worse for the
electro-dynamic effects. On the other hand, it is easy to exalt the electrostatic action as far as one likes by taking
more turns on the secondary, or combining self-induction and capacity to raise the potential. It should also be
remembered that, in reducing the current to the smallest value and increasing the potential, the electric impulses of
high frequency can be more easily transmitted through a conductor.
These and similar thoughts determined me to devote more attention to the electrostatic phenomena, and to endeavor
to produce potentials as high as possible, and alternating as fast as they could be made to alternate. I then found that

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I could excite vacuum tubes at considerable distance from a conductor connected to a properly constructed coil, and
that I could, by converting the oscillatory current of a condenser to a higher potential, establish electrostatic
alternating fields which acted through the whole extent of a room, lighting up a tube no matter where it was held in
space. I thought I recognized that I had made a step in advance, and I have persevered in this line; but I wish to say
that I share with all lovers of science and progress the one and only desire--to reach a result of utility to men in any
direction to which thought or experiment may lead me. I think that this departure is the right one, for I cannot see,
from the observation of the phenomena which manifest themselves as the frequency is increased, what there would
remain to act between two circuits conveying, for instance, impulses of several hundred millions per second, except
electrostatic forces. Even with such trifling frequencies the energy would be practically all potential, and my
conviction has grown strong that, to whatever kind of motion light may be due, it is produced by tremendous
electrostatic stresses vibrating with extreme rapidity.
Of all these phenomena observed with currents, or electric impulses, of high frequency, the most fascinating for an
audience are certainly those which are noted in an electrostatic field acting through considerable distance, and the
best an unskilled lecturer can do is to begin and finish with the exhibition of these singular effects. I take a tube in
the hand and move it about, and it is lighted wherever I may hold it; throughout space the invisible forces act. But I
may take another tube and it might not light, the vacuum being very high. I excite it by means of a disruptive
discharge coil, and now it will light in the electrostatic field. I may put it away for a few weeks or months, still it
retains the faculty of being excited. What change have I produced in the tube in the act of exciting it? If a motion
imparted to the atoms, it is difficult to perceive how it can persist so long without being arrested by frictional losses
; and if a strain exerted in the dielectric, such as a simple electrification would produce, it is easy to see how it may
persist indefinitely, but very difficult to understand why such a condition should aid the excitation when we have to
deal with potentials which are rapidly alternating. Since I have exhibited these phenomena for the first time, I have
obtained some other interesting effects. For instance, I have produced the incandescence of a button, filament, or
wire enclosed in a tube. To get to this result it was necessary to economize the energy which is obtained from the
field and direct most of it on the small body to be rendered incandescent. At the beginning the task appeared
difficult, but the experiences gathered permitted me to reach the result easily. In Fig. 34 and Fig. 35 two such tubes
are illustrated which are prepared for the occasion. In Fig. 34 a short tube T1, sealed to another long tube T, is pro-
vided with a stem s, with a platinum wire sealed in the latter. A very thin lamp filament I is fastened to this wire,
and connection to the outside is made through a thin copper wire w. The tube is provided with outside and inside
coatings. C and d respectively, and is filled as far as the coatings reach with conducting, and the space above with
insulating powder. These coatings are merely used to enable me to perform two experiments with the tube--
namely, to produce the effect desired either by direct connection of the body of the experimenter or of another body
to the wire w, or by acting inductively through the glass. The stem a is provided with an aluminium tube a, for pur-
poses before explained, and only a small part of the filament reaches out of this tube. By holding the tube T1 any-
where in the electrostatic field the filament is rendered incandescent.
A more interesting piece of apparatus is illustrated in Fig. 35. The construction is the same as before, only instead
of the lamp filament a small platinum wire p, sealed in a stem s, and bent above it in a circle, is connected to the
copper wire to, which is joined to an inside coating C A small stem st is provided with a needle, on the point of
which is arranged to rotate very freely a very light fan of mica v. To prevent the fan from falling out, a thin stem of
glass g is bent properly and fastened to the aluminium tube. When the glass tube is held anywhere in the
electrostatic field the platinum wire becomes incandescent, and the mica vanes are rotated very fast.
Intense phosphorescence may be excited in a bulb by merely connecting it to a plate within the field, and the plate
need not be any larger than an ordinary lamp shade. The phosphorescence excited with these currents is incom-
parably more powerful than with ordinary apparatus. A small phosphorescent bulb, when attached to a wire con-
nected to a coil, emits sufficient light to allow reading ordinary print at a distance of five to six paces. It was of
interest to see how some of the phosphorescent bulbs of Professor Crookes would behave with these currents, and
he has had the kindness to lend me a few for the occasion. The effects produced are magnificent, especially by the
sulphide of calcium and sulphide of zinc. From the disruptive discharge coil they glow intensely merely by holding
them in the hand and connecting the body to the terminal of the coil.
To whatever results investigations of this kind may lead, their chief interest lies for the present in the possibilities
they offer for the production of an efficient illuminating device. In no branch of electric industry is an advance
more desired than in the manufacture of light. Every thinker, when considering the barbarous methods employed,
the deplorable losses incurred in our best systems of light production, must have asked himself, What is likely to be
the light of the future? Is it to be an incandescent solid, as in the present lamp, or an incandescent gas, or a
phosphorescent body, or something like a burner, but incomparably more efficient?