Disc

“ A disc of card five inches in diameter, with six equidistant holes half an inch from the edge, answers well. The disc must be made to spin by any means very regularly at such a speed that the tuning-fork, or stretched string if this be used, when looked at through the holes, appears quiet, or nearly quiet, when made to vibrate. The separate drops will then be seen, and everything described in the preceding pages, and a great deal more, will be evident. This is one of the most fascinating [Pg 161] experiments, and it is well worth while to make an effort to succeed. ”

“ In each sector the same scene is represented, with this difference, that the movements of the objects are so arranged as to be progressive from one extreme to the other. The disc being fastened to the pin a b (fig. 3) by the screw v, with the figures facing outwards towards a, the whole apparatus is held before a looking-glass by the handle m. If the disc be now rotated by the button b, and the eye placed opposite one of the square holes in the card, the figures on the disc will appear to move more or less quickly according to the rate at which it is rotated. ”

“ On this pasteboard disc, paint in colors a number of frogs in relative and progressive positions of leaping; make between each figure a slit of about a quarter of an inch deep: and when this second disc is made to revolve at a foot distance behind the first, and the eye is placed near the slit, the whole of the figures, instead of appearing to revolve with the disc, will all appear in the attitudes of leaping up and down, increasing in agility as the velocity of the motion is increased. ”

“ Fortunately, you can satisfy yourselves on this point without any other materials than a cardboard disc and a piece of string. On this disc paint in small sections the [12] colors of the spectrum, repeating them four or five times in the following order: red, orange, yellow, green, blue, indigo, violet.
That the experiment may be entirely successful, the sections must be marked off according to the following scale of width of section. Let orange, next to the circumference represent 2: then
Now, in any diameter of the disc bore two holes not too near the edge. ”

“ The vibrations of the voice or of music, which reach the disc, cause this needle or point to rise or fall, producing impressions upon the tin foil or other substance. After the record has been made, duplicates are produced in a substance largely made of rubber, which is placed on a rotary disc or cylinder that is turned automatically, the needle or point attached to the disc working into the grooves and rising with or following the impressions, which cause the plate or disc to vibrate. The process is wholly mechanical, and electricity is not used. ”

“ By slipping one disc over another we can expose any given portion of each colour.100 These discs are placed on a top or teetotum, which is spun rapidly. The axis of the top passes through the centre of the discs, and the quantity of each colour exposed is measured by graduations on the rim of the top, which is divided into 100 parts. When the top is spun sufficiently rapidly, the impressions due to each colour separately follow each other in quick succession at each point of the retina, and are blended together ”

“ If the disc be caused to revolve rapidly, these two subjects will be seen at the same time, the image of each being held on the retina long enough to allow the other to take its place.
Some very beautiful combinations may be made by means of this instrument. For example, a horse may be on one side, and a man on the other, and, by spinning the disc, the man will be seen mounted on the horse. Then we may have a boat on one side, and a rower with his oars on the other. Similarly a mouse can be put into a trap, or a bird into a cage. ”

“ The soft parts are inclosed in a rounded, flattened disc, made of plates of carbonate of lime nicely fitted together. When living, the discs are covered with short spines. They are dark-yellow or whitish if bleached in the sun. ”

“ The easiest way of illustrating this is by means of a revolving disc, with sixteen holes pierced at regular intervals round the edge, and a jet of high-pressure air, which is forced through each of the holes successively as they revolve. When the disc does not quite complete one revolution in a second, only fifteen puffs come to the ear in a second of time, and they are heard as puffs; but when the rate reaches one revolution in a second, the [Pg 146] sound, as if by magic, changes into the lowest musical sound. ”

“ The upper disc is an elliptical opening, or aperture, which contains for every moment the stars visible upon the horizon, and the circumference is furnished with a graduated scale of hours divided into five-minute divisions, and this is fixed upon the apparatus. ”

“ In order to render the apparatus capable of transmitting different signals, two similar discs, on each of which was marked a number of words, letters, and figures, were attached to the seconds-arbors of two clocks beating dead seconds, and the discs were thus made to rotate synchronously before the operators at the two ends of the line. In front of either of these rotating discs was placed a fixed disc, perforated at one place, so that only one symbol was visible at a given time to either operator. ”

“ Thus both pieces of paper are now wet and are over the two glass discs. Pick up the piece of paper on the second tumbler, secretly taking with it the glass disc (which, of course, is under the paper) and place it on the top of the tube, taking great care not to let the glass disc "talk" against the top of the chimney; the audience must not hear the slightest "chink" of glass knocking against glass. ”

“ A disc of lead or iron, of the same diameter as the glass, and of approximately the proper curvature, is prepared by turning, and is armed with a handle projecting coaxially from the back of the disc. The glass revolving with moderate speed on the lathe, the lead tool, supplied with coarse emery and water, is held against it, care being taken to rotate the tool by the handle, and also to move it backwards and forwards across the disc, through a distance, say, up to half an inch; if it is allowed to overhang too much the edges of the glass disc will be overground. ”

“ In sand, and when the water power can be easily obtained, I prefer disc piles to screw piles, because there is hardly any chance of breaking or injuring the disc; you always know where the disc is, but cannot positively say where the screw is‌—‌it may be sound and may not be; in addition, the disc is stronger than a screw blade, as it can be strengthened by ribs almost as much as one likes, and the disc in sinking is hardly strained at all compared with a screw pile. ”

“ If a circular disc is painted with the prismatic colours taken in the same proportion with respect to each other in which they are exhibited in the spectrum made by the prism, and the wheel is turned swiftly, then the individual colours disappear, and nearly white light is apparent. ”

“ Several methods have been devised for recording sound and reproducing it in connection with the exhibition of motion pictures. A familiar one is the disc system, by which the sound vibrations are mechanically recorded upon and reproduced from discs by a stylus, which receives the sound vibrations for recording and transmits them from the disc to a loud-speaker in reproducing the sound.
Another method, important here, is the photographic film system, in which the sound vibrations are recorded upon a photographic record. ”

“ Having levelled the instrument, so as to render the disc concentric with the plate, and placed the index at zero, it is obvious that if an electric charge through the wire, h, reach the plate with the arms, it will electrify [Pg 127] the disc and index: the disc will have the opposite electricity, and the extremities of the index will take the same electricity as the arms, and consequently the index will describe an arc more or less great. The motion of the index is sufficiently slow to allow the eye conveniently to follow it. ”

“ We must first carefully draw a distinction between the vibrations of a plate or disc which is itself the source of sound, and those vibrations which are excited in a plate or disc by sound-waves otherwise originated. If a disc or plate of given size be set in vibration by a blow or other impulse it will give forth a special sound, according to the place where it is struck, or it will give forth combinations of the several tones which it is capable of emitting. ”

“ If you throw on the screen a circle of light, coloured by passing the rays from the electric lamp through chloride of chromium, the disc will then consist chiefly of red rays mixed with the rays which are absorbed by the yellow spot. If the observers in the darkened theatre look at the disc and wink slowly, they will see, with more or less distinctness, an illusion like red clouds floating over the disc, in consequence of most of the rays other than the red being absorbed by the yellow spots in their eyes. ”

“ Discs.—A job that will also afford good exercise is to turn up a disc with a groove in its face, and then chuck and turn another disk with an annular rib on its face to fit into the groove. This requires delicacy of measurement with the inside as well as the outside calipers.
The groove should be cut first, and the measurement taken from that, as it is less difficult to handle and set the tool for the rib than for the groove.
Lathe Speeds.—Do not make the too common mistake of running the mandrel at high speeds in your initial tests. It is far better to use a slow speed, and take a heavy cut. ”

“ The advantage of this method of mounting is the ease with which the disc may be moved, and so present every part of the object to the eye save that by which it is fastened to the disc. On this account it is often made use of when some particular subject is undergoing investigation, as a number of specimens may be placed upon the discs with very little labour, displaying all the parts. But where exposure to the atmosphere or small particles of dust will injure an object, no advantage which the discs may possess should be considered, and an ordinary covered cell should be employed. ”

“ A trifling character in the disc deserves notice; the barbs, for a space along one of the concentric zones are more or less destitute of their barbules, so that a part of the disc is surrounded by an almost transparent zone, which gives it a highly finished aspect. But I have elsewhere described [50] an exactly analogous variation in the hackles of a sub-variety of the game-cock, in which the tips, having a metallic lustre, "are separated from the lower part of the feather by a symmetrically shaped transparent zone, composed of the naked portions of the barbs." ”

“ Thus, “when the cavities above and below the iron disc of an ordinary telephone are filled with wadding, the instrument will transmit and speak with undiminished clearness. On placing a finger on the iron disc opposite the magnet, the instrument will transmit and speak distinctly, only ceasing to act when sufficient pressure is applied to bring plate and magnet into contact. Connecting the centre of the disc by means of a short thread with an extremely sensitive membrane, no sound is given out by the latter when a message is transmitted. ”

“ It may be said to have two distinct forms, the star and the disc, [2049] the former consisting of an indefinite number of radiating arms or leaves, the latter of a simple disc surrounded by a row of dots. In both forms it is found at all periods, not so much as a formal pattern in bands or groups, but as a decorative adjunct to surfaces within or without the field of the design, especially as a ground ornament on Ionic, Corinthian, and other early fabrics, or as an embellishment of the draperies worn by the figures on the vases.
FIG. 169. ROSETTE (RHODIAN) .
FIG. 170. ROSETTE (APULIAN) . ”

“ Every fresh disc of devices and disc of apertures of course opens up a new field of effect. Thus, if we take a disc bearing twelve repeats of a ball in the interior of a ring, each repeat being so painted that its position is advanced in the ring until it reaches in the twelfth ring the point whence it started, and place this on the back disc of the kalotrope, having previously removed the first one, no effect is observed when the wheel is rotated beyond the spreading out of the design and general appearance of hazy black circles. ”

“ This is known as Crookes' dark space.
Faraday's Disc.
A disc of any metal, mounted so as to be susceptible of rotation in a
magnetic field of force, with its axis parallel to the general direction
of the lines of force. A spring bears against its periphery and another
spring against its axle. When rotated, if the springs are connected by a
conductor, a current is established through the circuit including the
disc and conductor. ”

“ A metal arm carries an elastic metal disc called a receiving diaphragm, and to the back of this is attached a very delicate cutting-tool like a small chisel. By means of a screw the chisel and diaphragm are made to travel along the cylinder, and if no vibration is given to the disc the tool cuts a spiral on the recording cylinder, which is a clean groove with smooth bottom ploughed out of the soft composition. ”

“ Upon the disc is mounted a tiny mirror, and as the suspension of the disc is in the magnetic field held there by the strength of the field itself, it is extremely easily disturbed, so that a small beam of light reflected from the mirror can be vibrated with a very little current through great amplitude. ”

“ Any number of such discs can be combined so that each shows a sector at the top, and the angle of each sector can be varied at will by sliding the corresponding disc between the others. Maxwell used discs of two different sizes, the small discs being placed above the larger on the same pivot, so that one set forked a central circle and the other set a ring surrounding it. ”