Experiments On The Electrical Discharge In Vacuum Tubes

Friday, July 17, 1891
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THE ELECTRICIAN, JULY 17, 1891. Q97 “I have found that it is preferable to use i|\ these experiments an alternate current machine, giving a moderate number of alternations per second, to excite the induction coil for charging the Leyden jar which discharges through the primary shown diagrammatically in Fig. 4, as in such case, before the disrup- tive discharge takes place, the tubs or bulb is slightly excited and the formation ofthe luminous circle is decidedly facilitated. But I have also used a Wimslmrst machine in some experi- ments. “ Prof. J. J. 'l`homson’s vie\v of the phenomena under con- sideration secms to be that they are \vhol|y due to electro magnetic action. I was, at one time, of the same opinion, but upon carefully investigating the subject l was led to the conviction that they are more of an electrostatic nature. In support of my vie\v I will describe a fe\v experiments But the circles were always in close proximity to the primary, and were considerably easier produced when the latter was very close to the glass. “Another observation made by me was that when the specific inductive capacity of the medium between the primary and secondary is increased, the inductive elllect is augmented. I have likewise noted that when a bulb is surrounded by a wire closed upon itself and in the plane of the primary, the forma- tion of the luminous circle within the bulb is not prevented. But if, instead of the wire, a broad strip of tinfoil is glued upon the bulb, the formation of the huuinous band was prevented. “Some ofthe experiments of Prof. J. J. Thomson also would seem to show some electrostatic action. For instance, in the experiment with the bulb enclosed in a bell jar, I should think that when the latter is exhausted so far that the gas enclosed reaches the mnxinnnn conductivity, the formation of the circle in the bulb and jar is prcvcntcd because of thc space surround- > l ' " Fm. I5 made by me. To excite luminosity in the tube it is not should be closed. absolutely necessary that the conductor For instance, if an ordinary exhausted tube (preferably of large diameter) be surrounded by a spiral of serving as the primary, a fecbly hnniuous duced in t-he tube, roughly sho\vn in l~`ig. 5. thick copper wire spiral may be in- ln one of these experiments a curious phcuonienou wus observed ; namely, two intensely luminous circles, each of tlnuu closc to n turn of tho tnbo, and I attri- of nodes on the a faint luminous primary spiral, were former] inside of the huted this phenomenon to the existence primary. 'l`hc circles wcrc connected by spiral, parallel to the primary and in closc proximity to it. To produce this ellect I have found it necessary to strain the jar to the utmost. The turns of the spiral tend to close and form circles, but this, of course, would he expected, und does not the the necessarily indicate an elcctro~nnxgne|ic ellccr.; whereas fact that a glow can be produced along the primary in form of an open spiral argues for nn electrostatic cllcct. ' é Pllluliv in LAM CWD l"|o. 4. “Another experiment performed is illustrated in Fig. 6. In this case an ordinary lamp»bulb was surrounded by one or t\vo turns of thick copper wire, P, and a luminous circle, Ii, excited in the bulb by discharging the jar through the primary. 'l‘he lamp-bulb was provided with a tinfoil coating on the side oppo- site to the primary, and each time the tinfoil coating \vas con- nected to the ground, or to a large object, thc luminosity of the circle was considerably increased. 'l`his was evidently duo to electrostatic action. “In other experiments I have noted that when the primary touches the glass the luminous circle is easier produced and is more sharply defined; but I have not notcd that, generally speaking, the circles induced were very sharply dehned, as Prof. .I. J. Thomson has observed; on the contrary, in my expe- riments, they were broad, and often the \Vll0l8 of the bulb or t\\be was illuminated; and in one case I have observed an in- tensely purplish glow, to which Prof, .l. .|. Thomson refers, l ./7 ' Fm 5 ing the primary being highly conducting; when the jar is further exhausted the conductivity oi the space around the primary diminishes, and the circles appear necessarily first in the bell jar as the rarciied gas is nearer to the primary. But were the inductive ell`ect very powerful they would probably to the highest degree they would very likely show themselves in the bulb only-that is, supposing thc vacuous space to he appear in the bulb also. lf, however, thc bell jar were exhausted P ~ tv iii llll Fm. 6 noirconducting. (ln the assumption that in these phenomena electrostatic actions arc concerned we find it easily explicable why tho introduction of mercury or the heating of tho bulb prevents the formation of the luminous band or shortens the after-glow ; and also why, in some cases, a platinum wire may prevent the cxcitation of the tube. Nevertheless some of the experiments of Prof. J. .l, ’l‘homson would seem to indicate an electromagnetic ellizct. I may add that in one of my experi- mcuts in which a vacuum was produced in tho 'l‘oriccl|ian method, l was unable to produce the luminous band, but this may have been due to the weak exciting current employed. “My principal urgumcnt is the following: I have experi- mentally proved that if thc same discharge which is barely sullicicnt to excite a luminous band inthe bulb when passed through the primary circuit be so directed as to exalt the elec- trostatic inductive e|l`ectnn exhausted tube, devoid of electrodes, may be excited at a distance of several feel."

295 THE ELEQLEJIAN, JULY 17, 1891. __»**V _ ’l**~ EXPERIIVIENTS ON THE ELECTRIC DISCHARGE IN VACUUM TUBES. 'l`hc beautiful and suggestive experiinents on the electric discharge in vacuum tubes, shown by l‘rof, .l. J. Thomson on the occasion of the visit of the Physical Society to Cambridge, ln May, have excited considerable attention, and the illustrated account of them, which appeared in The Electrician of May 22nd, has been widely reproduced both in America and in France. In America thc publication of Prof. 'l‘homsou’s experi- ments has resulted in some interesting contributions to the Elec-t1-:'crzl En;/1‘:w¢'r ol' New York, by I’rof. Elihu Thomson and Mr. Nikola Tesla, who appear to have been pursuing the same fruitful line of research. The raison ¢I’€tr~c and the practical bearing of the phenomena described are not as yet apparent, but they seem to he of the order likely to yield valuable re suits both to thc devotee of pure science and the patentee; indeed, Mr. Nikola Tesla has already brought the results of some of those striking experiments of his recently made public within the cognisance of the American Patent Ufiice. How- ever simple the future explanation, and however far-reaching the possible practical applications of these phenomena may be, they appeal at present. mainly to the students of pure science, and to them the following notes by l’rof. Elihu Thomson and Mr. Nikola Tesla will bc of interest :-- “1 have been much interested,” says Prof. Elihu Thomson, in the New York Elfcfmfml Enyinrcr of June 2-ith, “in the account of novel phenomena given under the title ‘Some lixperiments on the Electric Discharge in Vacuum Tubes,’ by Prof. J. J. Thomson, inasmuch as several months ago I tried the same, or a very similar, experiment. Briefly, my experi- ment was performed with a closed ring made of a. glass tube about one inch in diameter, the external diameter of the ring being about six inches. This was exhausted and laid alongside of a single turn of heavily insulated wire, which formed part of the discharge path from thc outside of a Leyden jar, arranged to bc charged and discharged rapidly by a Toepler- Iloltz machine. lt was found that at every discharge of the jar there was a discharge in the tube giving a baud of light in the vacuous space. The accompanying engraving _(Fig. l) shows the arrangement of apparatus as just described, \`uriously enough, the experiment of l’rof. J. .l. Thouison, in which a small pellet of mercury in an exhausted tube stopped the discharge, had its counterpart in my own experiments, as follows :-I had constructed a two-way discharge tube (Fig. fl). Ono branch, a, was large in diameter, and the branch b \vas__of barometer-tube section. Wires sealed at r, fl enabled a dis- charge to be passed. A small globule of mercury was placed in the tube, and could be shaken down into the barometer tube “.i and out into the large tube at will. Though the discharge would not always divide and pass through both tubes from c to rl, it sometimes did; but the intcrpositiou of the mercury globulc in the small tube stopped the discharge through it. Mr. Nikola Tesla, writing to the same journal (Elecmbul Eng/iuefr of New York, .lilly 1), says:»“I have noted the description of some experiments of Prof. J. J. Tliomsoii, on the ‘Electric Discharge in Vacuum Tubes,” and in your issue of Juno 24th, Prof. Elihu Thomson describes un experi- ment of the same kind. 'I‘no following lilies are not panned \vith any desire on my part to put myself on record as one who has performed similar experiments, but with a desire to assist other oxperimenters by pointing out certain peculiarities of the phenomena observed, which, to all appearances, have not been noted by Profl J. J. Thomson, \Vll0, however, seems to have gone about systematically in his investigations, and \vho has been the first to make his results known. These peculiarities noted by me would seem to be at variance with the views of Prof. J. J. Thomson, and present the phenomena in a different light. ¢\_._.._. 0 ' I"1o. 2. “ My investigations occupied me principally during the winter and spring of the past year. During this time many different experiments were performed. Fig. 3 may serve as an example of one of the many forms of apparatus used. This consisted of a large glass tube, sealed at one end and projecting into an ordinary incandescent lamp bulb. The primary, usually consisting of a few turns of thick, well-insulated copper sheet, was inserted within the tube, the inside space of the bulb fur- nishing the secondary. This form of apparatus was arrived at after some experimenting, and was used principally with the view of enabling me to place a polished reflecting surface in the inside of the tube, and for this purpose the last turn of the primary was covered with a thin silver sheet.