Cimeter

“ The focal length of the objective and the distance between the optical centre of the lens and the webs are so arranged that images of the divisions are formed in the plane of the webs, and the pitch of the screw is such that one division of the scale corresponds with some whole number of revolutions of the screw.
There is what is technically called a “comb” inserted in the micrometer box at d (fig. 14) —its upper surface being nearly in the plane of the wires. ”

“ The small drum-head T opposite the micrometer head S turns a screw which acts upon a short cylinder that cannot turn but can move only in the direction of the axis of the micrometer screw. The end-plane of this cylinder receives the pressure of the micrometer screw, so that by turning the small drum-head the coincidence-reading of the movable web with the fixed web can be changed, and thus any given angle can be measured with different parts of the micrometer screw in order to eliminate the effects of periodic error of the screw. ”

“ The cathetometer telescope has a lens of such a focus that 1 mm. on the wood section becomes 0.25 mm. in the focus. The micrometer has a screw-thread with a pitch of 0.25 mm., so that one revolution of the micrometer head moves the thread through exactly 1 nun. as seen on the wood. The individual measures of rings are made on the micrometer screw by reading the graduation of the head to revolutions and hundredths, giving directly millimeters and hundredths. ”

“ The Chemist's voice came to him from far away. "We are all of us here in a world that only occupies a portion of one little atom of the gold of a wedding-ring. Yet what you see there in that stone——"
The Very Young Man raised his head. Before him stood the microscope, with its fragment of stone gleaming in the blue light of the burning wire. ”

“ Gentlemen, I want to make clear to you now—as clear as I can—the peculiar aspect of everything that I saw under this microscope. I seemed to be inside an immense cave. One side, near at hand, I could now make out quite clearly. The walls were extraordinarily rough and indented, with a peculiar phosphorescent light on the projections and blackness in the hollows. I say phosphorescent light, for that is the nearest word I can find to describe it—a curious radiation, quite different from the reflected light to which we are accustomed. ”

“ In the measuring machines in general use the field of view, as in the case of the glass-scale micrometer, is sufficiently large to include the image of the 5 mm. square. The microscope or viewing telescope is fitted with a spider-line micrometer having two screws at right angles to each other, by means of which readings can be made first on one réseau-line, then on the star, and finally on the opposite réseau-line in both co-ordinates. ”

“ The draft of a chimney is the current of air created by the difference in pressure resulting from variation in weight between the relatively hot gases in the flue and the cooler outside air. The strength or intensity of the draft depends, for the most part, on the height of the chimney, and the temperature difference between the chimney gases and the outside atmosphere. The draft is not so good in summer as in winter because the difference in temperature between the outside air and the gases in the flue is less. ”

“ Gamma rays are absorbed in any material through which they pass, according to its density. A low radiation count at the detector indicates a high-density sediment: More radiation is absorbed and less is reflected back to the detector. Conversely, a high count indicates low density. Data are recorded on special cold-resistant film. A number of different sediment measurements can be made in several locations before the unit must be returned to the surface. ”

“ I devised a very satisfactory method for determining the quantity of radium by the means of a radioactive gas produced by it and called "emanation." This method, frequently used in my laboratory, permits of the measurement of very small quantities of radium (less than a thousandth of a milligramme) , with a fair precision. More important quantities are often measured by their penetrating radiation, named Gamma-rays. For this we also possess in my laboratory a suitable equipment. It is easier and more satisfactory to measure the radium by the emitted rays, than to weigh it in a balance. ”

“ Very remarkable forms of these cells may be found in the skin of the cuttle-fish.
Figs. 24 and 25 are two examples of coal, the former being a longitudinal and the latter a transverse section, given in order to show its woody character. Fig. 17 is a specimen of gold-dust intermixed with crystals of quartz sand, brought from Australia; and Fig. 21 is a small piece of copper-ore.
Every possessor of a microscope should, as soon as he can afford it, add to his instrument the beautiful apparatus for polarising light. ”

“ To the engineer the instrument is invaluable; we have explained elsewhere how necessary it is that various metals and mixtures of metals should be examined for fractures. Under the high magnification with the ordinary microscope, even with an instrument specially designed for the work, only a very small area can be studied at once. With the micro-telescope a relatively large area may be examined under a high magnifying power. ”

“ With the very weak radiation that I have used for my experiments, corresponding to the ordinary radiographic and radioscopic work, it has been easy for me to obtain images of metallic objects and human bones placed on a sensitive plate 15 feet from the radiating source, although the rays pass directly through a slab of marble an inch thick, a sheet of lead one-tenth of an inch thick, and a flooring eight inches deep, built of oak boards and rough plaster. ”

“ For temperatures above a red heat the only feasible metals to use are platinum or the more expensive metals of the platinum series—and hence platinum is universally employed for this purpose. The original Siemens pyrometer consisted of 1 metre of platinum wire, 1 millimetre in diameter, wrapped round a porcelain rod, and protected from furnace gases by an iron sheath An elaborate method of measuring the resistance, involving the electrolysis of acidulated water, was adopted for workshop use, but was too involved to become popular. ”

“ All these, except one or two, are liquid, and must be kept in stoppered bottles, or, at least, as free from the action of the air as possible.
When any two substances are to be united firmly, I have termed the medium employed “a cement;” but often the appearance of the slides is thought to be improved by drawing a coloured ring upon them, extending partly on the cover and partly on the slide, hiding the junction of the two. The medium used in these cases I term a Varnish, and hereinafter mention one or two. Of course, the tenacity is not required to be so perfect as in the cements. ”

“ When a number of instruments are in use, it is advisable to keep a standard pyrometer for checking purposes, preferably one which has been certified by the National Physical Laboratory. In conducting a test, the couples, with protecting-tubes removed, may be placed in the tube of an electric furnace of the type shown in fig. 29, in close proximity with the standard junction. On raising the temperature gradually, the readings of each working instrument may be compared with the standard, and the necessary corrections discovered. ”

“ For the first demonstration, I will convert the cube into its radiation equivalent, send the radiation down the length of the laboratory, and reassemble it at the receiving equipment down there. Once this has been done, I have a number of other objects to transmit, in increasing complexity. For instance, there is a pair of pliers to show that alloy steels can be faithfully reproduced, and also that a moving joint can be maintained. We have a cheap alarm clock to show that the energy coiled in the mainspring can be transmitted without much loss, if any. ”

“ The moveable screw at the bottom of the cistern is for the purpose of forcing the mercury to the top of the tube when the instrument is being carried from place to place, and it must always be unscrewed to its utmost limit when the barometer is hung in its proper place. ”

“ The open end of the tube is fixed into an iron cylinder, which forms the cistern of the barometer. Iron has no action upon mercury, and is therefore used instead of any other metal. One or two holes are made in the top of the cistern, which are covered on the inside with strong sheep-skin leather, so as to be impervious to mercury, but sufficiently porous for the outer air to act upon the column. The cistern is of capacity sufficient to receive the mercury which falls out of the tube until the column stands lower than the scale reads ”

“ The declination circle reads from the eye-end, and four handles for clamping Repsolds’ small equatorial. and slow motion in right ascension and declination are situated near the observer’s hands. The tube is of sheet steel, light, stiff, and free from tremor. The eye-end carries the micrometer with an illuminating apparatus similar to that described under Micrometer. The lamp near the eye-end illuminates the field or the wires at pleasure, as well as the position circle of the micrometer and the declination circle; a separate lamp illuminates the hour circle. ”

“ Figure 7.—“Schweigger multiplier” used by Oersted in 1823. A thin magnetic needle is held in a light, paper sling at F, suspended by a fine, vertical fiber. (From Annales de Chimie et de Physique.)
Cumming considers his straight-wire calibrated “galvanometer” to be a device for “measuring” galvanic electricity; on the other hand, his multiple-loop “galvanoscopes” are for “discovering” galvanic electricity. With the multiplier instrument, he found galvanic effects (i.e., needle deflections) using copper and zinc electrodes with several acids not previously known to create galvanic action. ”

“ Now for a word as to Professor Michelson’s suggestion that an unvarying unit of measurement may be found in a certain light-wave, as observed in the interferometer. Everybody knows that each chemical element burns with colors of its own. When we see red fire bursting from a rocket we know that strontium is ablaze; when the tint is green it [218] tells us that copper is on fire, as when a trolley-wheel jumps from its electric wire. ”

“ Measurement of Low Temperatures.—Junctions of iron and constantan, Hoskin’s alloys, copper and German silver, or copper and constantan, are suited to these measurements. In a laboratory the cold junction may be kept in ice in a Dewar vessel, the mechanically protected form known as the “Thermos” flask being very useful for this [98] purpose. With a good mirror galvanometer precise readings may be secured, 1/10 of a degree C. being easily detected. ”

“ It is the fundamental premise of instrument-science that a device for detecting or measuring a physical quantity can be based on any phenomenon associated with that physical quantity. Although the instrumentation of electrostatics in the 18th century, for example, relied mainly on the phenomena of attraction and repulsion and the ubiquitous sparks and other luminosities of frictional electricity, even the physiological sensation of electric shock was exploited semiquantitatively by Henry Cavendish in his well-known anticipation of Ohm’s researches. ”

“ The rectangular closed cistern that shall hold a given quantity of water and yet have the smallest possible surface of metal must be a perfect cube—that is, a cistern every side of which is a square. For 1,000 cubic feet of water the internal dimensions will be 10 ft. × 10 ft. × 10 ft., and the zinc required will be 600 square feet. In the case of a cistern without a top the proportions will be exactly half a cube. ”

“ On the other hand, to make a radiograph of the bones, a lower vacuum is necessary in order to get a contrast between the bones and the tissues. In general, a high vacuum is best for fluoroscope work and a low vacuum for making pictures on a photographic plate. Short exposures in radiography are obtained by powerful rays and consequently by coils operating at considerable energy. In extended examinations or where a subject is under the X-rays for more than a minute or so, a screen should be interposed between the subject and the tube to avoid the burning effect which is often noticeable. ”

“ The existing condition of a furnace may be discovered by taking a number of cylinders, having progressive melting points, and making observations after the manner described under the heading of Seger pyramids. A few “Sentinel” cylinders are frequently of use in the workshop or laboratory for other [209] purposes, such as a rapid check of a given temperature in confirmation of the reading of an indicating pyrometer, or in discovering whether a certain temperature has been exceeded in a given case. ”

“ Joly’s Meldometer.—This device, due to Dr Joly, is intended for laboratory determinations of melting points. It consists of a strip of platinum, heated by electricity, upon which a tiny fragment of the material is placed, which is viewed through a microscope. The temperature of the platinum is regulated by means of a rheostat in the circuit, and in making a test the temperature is gradually raised until [221] the material is observed to become globular, or to flow over the platinum strip. ”

“ What would any engineer, or simple worker in metal, wood, or stone, think of an alleged standard measure or cubit [Pg 272] which varied so enormously from its own alleged length? But, surely, such facts and such results require no serious comment.
In this, his latest communication on the Pyramids, Professor Smyth also offered some new calculations regarding the measurements of the interior of the broken stone coffin standing in the King's Chamber. Formerly (1864) , he elected the cubic capacity of this sarcophagus to be 70,900 "pyramidal" cubic inches ”