Crookes tube

“ Robb. The Crookes tubes used in this and in most of Dr. Robb's experiments are considerably larger than any I have seen elsewhere, being pear-shaped, about eight inches long, and four inches wide at the widest part. It is, perhaps, to the excellence of this tube that Dr. Robb owes part of his success. At any rate, in the foot picture the bones are outlined through shoe and stocking, while every nail in the sole of the shoe shows plainly, although the rays came from above, striking the top of the foot first, the sole resting upon the plate-holder. ”

“ In making this picture, Professor Pupin excited his tube by means of a powerful Holtz machine, thus following Dr. Morton in the substitution of statical electricity for the more common induction coil.
Professor Pupin sees no reason why the whole skeleton of the human body should not be shown completely in a photograph as soon as sufficiently powerful bulbs can be obtained. He thinks that it would be possible to make Crookes tubes two feet in diameter instead of a few inches, as at present. ”

“ It might be possible, Professor Wright thinks, to get good results by using, instead of the Crookes tube, a large sphere of aluminium, which is more transparent to the new rays than glass and possesses considerable strength. It is a delicate question, however, whether the increased thickness of metal necessary to resist the air pressure upon a vacuum would not offset the advantage gained from the greater size. Moreover, it is a matter for experiment still to determine, what kind of an electric current would be necessary to excite such a larger tube with the best results. ”

“ A brilliant green light is often one of the signs of wrong connection, and particularly so when the little shadow on the chemical bulb is absent. Never run these or any other tubes backwards, but be sure the current is flowing in correct direction at first operation.
Other forms of Crookes tubes differ only in form, or are devoid of adjustment, and the connections of coil, tube, etc., are the same.
General Remarks.
A high vacuum gives greater penetrative power than a low vacuum. ”

“ It was a puzzle to Carnes, and even Dr. Bird, although he could grasp the principle at a glance, was at a loss to divine its use. From a set of coils attached to a generator was connected a tube of the Crookes tube type with the rays from it gathered and thrown by a parabolic [14] reflector onto the space where a man's head would rest when he was seated in a white metal chair with rubber insulated feet, which stood beneath it. An operating table occupied the other side of the room while a gas cylinder and other common hospital apparatus stood around ready for use. ”

“ A Crookes tube of special design is energized from a coil or similar electrical distributor, and by means of the resultant rays otherwise opaque objects appear partially transparent, their shadows being cast upon the screen of a fluoroscope, or these shadows are allowed to act upon a sensitized photographic plate, and subsequent development reveals outlines or shadowgraphs. ”

“ The second essential is the glass tube. The one in common use is the Crookes tube, usually pear-shaped, and resting upon a stand. Into it is inserted two aluminum electrodes or disks, the one through the smaller end of the tube being used as the cathode, and the one from below and near the large end being used as the anode. (3.) A fluoroscope with which to observe the conditions inside the tube necessary to the production of the X ray, to decide upon its proper intensity, and to establish the proper degree of fluorescence. ”

“ The waves of long period from a Crookes tube would pass through wood, paper, or the human body, without much resistance, but would be absorbed or reflected by the denser metals. But if objects capable of taking up their vibrations lay in the path of these long rays they would set them vibrating like the violin string, and might in the same way produce overtones which did not before exist. ”

“ When the induction spark is first turned on nothing is visible—the vacuum is so high that the tube is non-conducting. I now warm the potash slightly and liberate a trace of aqueous vapor. Instantly conduction commences, and the green phosphorescence flashes out along the length of the tube. I continue the heat, so as to drive off more gas from the potash. The green gets fainter, and now a wave of cloudy luminosity sweeps over the tube, and stratifications appear, which rapidly get narrower, until the spark passes along the tube in the form of a narrow purple line. ”

“ W. K. Roentgen, a professor of physics at Wurzburg. He covered a highly-exhausted Crookes’ tube with black cardboard, and found that when the discharge of a large induction coil was passed through the tube in a dark room, a piece of paper coated on one side with platino-cyanide of barium, and held near the covered tube, glowed with a brilliant fluorescence, no 447matter which side of the paper was turned towards the tube ”

“ Crookes's vacuum tube was got into the right position—I saw that the rays worked well—then I returned to Gopinath.
“Come with me,” I said.
He followed me into my laboratory without a word. I desired him to strip, and then after some difficulty arranged him in such a position that the rays should pass through his body. I turned off the light in the room—my electrical battery worked well, the rays played admirably in the vacuum tube. I removed the cap from the camera, and after an exposure of from seven to ten minutes, felt certain that I had taken a careful photograph. ”

“ Radiant matter in these high vacua is not only excited by the negative pole of an induction-coil, but a hot wire will set it in motion with force sufficient to drive round the sloping vanes.
Radiant Matter is deflected by a Magnet.—I now pass to another property of radiant matter. This long glass tube (Fig. 14) is very highly exhausted; it has a negative pole at one end (a) and a long phosphorescent screen (b, c) down the center of the tube. ”

“ The wonderful X-ray, and the rich scientific harvest which has followed the discovery by Röntgen of invisible radiation from a vacuum tube, was preceded by much investigation of the effects of electric discharges in vacuum tubes, and Hittorf, followed by Crookes, had given special study to these effects in very high or nearly perfect vacua. Crookes, though especially enriching science by his work, missed the peculiar X-ray, which, nevertheless, must have been emitted from many of his vacuum tubes, not only in his hands, but in those of subsequent students. ”

“ Crookes for making air-tight connections between separate pieces of apparatus when a rigid connection would have been unnecessary and inconvenient. By the use of such spiral tubes it is possible to combine comparatively free movement with all the advantages attached to hermetically-sealed joints.
To make a flexible spiral tube, mount a copper cylinder on a screw, so that the cylinder will travel in the direction of its axis when it is rotated. ”

“ The pieces f g on the end of one beam consist of platinum-foil exposing a square centimetre of surface, while the extremities f' g' on the other beam consist of pith-plates of the same size. A wide beam of radiation thrown in the centre of the tube on to the plates g f' causes g to be attracted and f' to be repelled, as shown by the light reflected from the mirrors, c c'. The atmospheric pressure in the apparatus is equal to about forty millimetres of mercury. ”

“ At each end of the tube, and rather above the center, is an aluminium pole, so that whichever pole is made negative the stream of radiant matter darts from it along the tube, and striking the upper vanes of the little paddle-wheel, causes it to turn round and travel along the railway. ”

“ I first turn on the induction-coil slightly, so as not to bring out its full power. The focus is now playing on the metal, raising it to a white-heat. I bring a small magnet near, and you see I can deflect the focus of heat just as I did the luminous focus in the other tube. By shifting the magnet I can drive the focus up and down or draw it completely away from the metal and leave it non-luminous. I withdraw the magnet, and let the molecules have full play again; the metal is now white-hot. I increase the intensity of the spark. ”

“ A light beam, A B, having two square inches of pith, C, at one end, is balanced on a very fine fibre of glass, D D', stretched horizontally in a tube; one end of the fibre being connected with a torsion handle, E, passing through the tube, and indicating angular movements on a graduated circle. The beam is cemented to the torsion fibre, and the whole is inclosed in glass, and connected with the mercury pump by a spiral tube, F, and exhausted as perfectly as possible. G is a spiral spring, to keep the fibre in a uniform state of tension, H is a piece of cocoon silk. ”

“ In the vessels with the lower degree of exhaustion, the length of the mean free path of the molecules is exceedingly small as compared with the dimensions of the bulb, and the properties belonging to the ordinary gaseous state of matter, depending upon constant collisions, can be observed. But in the phenomena now about to be examined, so high is the exhaustion carried that the dark space around the negative pole has widened out till it entirely fills the tube. ”

“ The dark space will be in the center. When the exhaustion is not very great, the dark space extends only a little on each side of the negative pole in the center. When the exhaustion is good, as in the tube before you, and I turn on the coil, the dark space is seen to extend for about an inch on each side of the pole.
Here then, we see the induction-spark actually illuminating the lines of molecular pressure caused by the excitement of the negative pole The thickness of this dark space is the measure of the mean tree path between successive collisions of the molecules of the residual gas. ”

“ The same effects were produced in inverse order, the point of neutrality being when the gauge was about seven millimetres below a vacuum.
A piece of ice produced exactly the opposite effect to a hot body.
The presence of air having so marked an influence on the action of heat, an apparatus was fitted up in which the source of heat (a platinum spiral rendered incandescent by electricity) was inside the vacuum-tube instead of outside it as before; and the pith-balls of the former apparatus were replaced by brass balls. ”

“ When the sulphide is exposed to light—even candle-light—it phosphoresces for hours with a bluish-white color. It is, however, much more strongly phosphorescent to the molecular discharge in a good vacuum, as you will see when I pass the discharge through this tube. ”

“ It has been ascertained that the cause of phosphorescence is in some way connected with the hammering of the electrons, violently driven from the negative pole on to the surface of the body under examination, and so great is the energy of the bombardment, that impinging on a piece of platinum or even iridium, the metal will actually melt. When the diamond is thus bombarded in a radiant matter tube the result is startling. It not only phosphoresces, but becomes discoloured, and in course of time becomes black on the surface. ”

“ It seemed as if the true action of the heat was one of attraction, instantly overcome by ascending currents of air. A hot metal or glass rod and a tube of hot water applied beneath the pith-ball at b produced the same effect as the flame; when applied above at a they produced a slight rising of the ball. ”

“ There does not seem, therefore, any advantage in supplying a Crooke’s tube with an aluminum window. The mechanical difficulties, too, in accomplishing this are very great. There is no way of joining the thin aluminum disk to the glass so that an air-tight joint can be made. In the process of exhausting the Crooke’s tube, the tube must be heated to a comparatively high temperature in order to drive off the air which clings to the inside of the glass. The rise of temperature would soften or melt any current which might be used to make the aluminum adhere to the glass. ”

“ If I put more powder in the gun, the velocity will be greater and the trajectory flatter; and if I interpose a denser resisting medium between the gun and the target, I diminish the velocity of the shot, and thereby cause it to move in a greater curve and come to the ground sooner. I can not well increase before you the velocity of my stream of radiant molecules by putting more powder in my battery, but I will try and make them suffer greater resistance in their flight from one end of the tube to the other. ”

“ Though three fall tubes are recommended, it must not be supposed that the pump will produce a Crooke's vacuum three times more rapidly than one fall tube. Until the mercury commences to hammer in the pump the three tubes will pump approximately three times faster than one tube, but as soon as the major portion of the air collected begins to come from the layer condensed on the glass surface of the tube to be exhausted and from the electrodes, the rate at which exhaustion will go on no longer depends entirely on the pump. ”

“ Pipes led from the latter, one to the tun, the other along the passage under the wharf. On the side of the tun and connected to it at top and bottom was a vertical glass tube protected by a wooden casing, evidently a gauge, as beside it was a scale headed “gallons,” and reading from 0 at the bottom to 2,000 at the top. A dark-colored liquid filled the tube up to the figure 1,250. There was a wooden spigot tap in the side of the tun at floor level, and the tramline ran beneath this so that the wheeled kegs could be pushed below it and filled. ”