William Arnold Anthony

“ By its aid we may frequently modify some of the conditions, known to be conditions, in such ways that the phenomenon is not arrested, but so altered in the rate with which its details pass before us that they may be easily observed. Experiment also often leads to new phenomena, and to a knowledge of activities before unobserved. Indeed, by far the greater part of our knowledge of natural phenomena has been acquired by means of experiment. To be of value, experiments must be conducted with system, and so as to trace out the whole course of the phenomenon. ”

“ In conducting our experiments, and in reasoning upon them, we are often guided by suppositions suggested by previous experience. If the course of our experiment be in accordance with our supposition, there is, so far, a presumption in its favor. So, too, in reference to our reasonings: if all our facts are seen to be consistent with some supposition not unlikely in itself, we say it thereby becomes probable. ”

“ Physics deals with all those phenomena of matter which are not directly related to chemical changes. Astronomy is thus a branch of Physics, yet it is usually excluded from works like the present on account of its special character. ”

“ Measurements.—All the phenomena of Nature occur in matter, and are presented to us in time and space. Time and space are fundamental conceptions: they do not admit of definition. Matter is equally indefinable: its distinctive characteristic is its persistence in whatever state of rest or motion it may happen to have, and the resistance which it offers to any attempt to change that state. ”

“ Transfer of Heat.—In the preceding discussions it has been assumed that heat may be transferred from one body to another, and that if two bodies in contact be at different temperatures, heat will be transferred from the hotter to the colder body. In general, if transfer of heat be possible in any system, heat will pass from the hotter to the colder parts of the system, and the temperature of the system will tend to become uniform. ”

“ Measure of the Counter Electromotive Force of Decomposition.— In the general formula developed in § 377 the quantity represents the energy expended in the circuit which does not appear as heat developed in accordance with Joule's law. In the present case it is the energy expended during electrolysis in decomposing chemical compounds and in doing mechanical work. In many cases the mechanical work done is not appreciable; but when a liquid like water is decomposed into its constituent gases, work is done by the expansion of the gases from their volume as water to their volume as gases. ”

“ Those bodies which exhibit electrolysis are always such as have considerable freedom of motion among their molecules. Ordinarily, they are liquids or solids in solution or fused. The discharge through gases is also probably accompanied by electrolysis. Bodies which can be decomposed were called by Faraday, to whom the nomenclature of this subject is due, electrolytes. The current is usually introduced into the electrolyte by solid terminals called electrodes. The one at the higher potential is called the positive electrode or anode; the other, the negative electrode, or cathode. ”

“ Concerning the ultimate modes of existence or action, we know nothing whatever; hence, a law of nature cannot be demonstrated in the sense that a mathematical truth is demonstrated. Yet so great is the constancy of uniform sequence with which phenomena occur in accordance with the laws which we discover, that we have no doubt respecting their validity. ”

“ Divisions of Natural Science.—Everything which can affect our senses we call matter. Any limited portion of matter, however great or small, is called a body. All bodies, together with their unceasing changes, constitute Nature. ”

“ The secondary cell of Planté is an example of a cell made directly by electrolysis, as has been assumed in the preliminary discussion. The electrodes are both lead plates, and the electrolyte dilute sulphuric acid. When a current is passed through the cell, the oxygen evolved on the anode combines with the lead to form peroxide of lead, which coats the surface of the electrode. When the cell is inserted in a circuit, a current is set up, the peroxide is reduced to a lower oxide, and the metallic lead of the other plate is oxidized. ”

“ If a current be sent through the series of cells containing these solutions, the same number of univalent, ions will be liberated in each. The difference of potential between the terminals of the cells will be in general different for each of them. We have from Ohm's law the relation where the current is the same for each cell and the difference of potential and the conductivity (§ 275) different for the different cells. Now consider a cross-section in one of the cells parallel with the electrodes; let and represent the velocities of the ions evolved in this cell. ”

“ It was proved by Franklin that the lightning flash is an electrical discharge between a cloud and the earth or another cloud at a different electrical potential. The differences of potential to which such discharges are due must be enormous, and the heat developed by the discharge shows that the quantity of electricity which passes in it is considerable.
Slowly moving fire-balls are sometimes seen, which last for a considerable time and disappear with a loud report and with all the attendant phenomena of a lightning discharge. ”

“ The body of the tube is filled with a faint rosy light, which in many cases breaks up into a succession of bright and dark layers transverse to the direction of the discharge. The discharge in this case is called the stratified discharge. A vacuum-tube m which the exhaustion is such that the phenomena are those here described is often called a Geissler tube. As the exhaustion is raised still higher, the rosy light in the tube fades out, the non-luminous space around the negative electrode becomes very much greater, and the phenomena in the tube become exceedingly interesting. ”

“ The Spark, Brush, and Glow Discharges.—When a conductor is charged to a high potential and brought near another conductor which is joined to ground, a spark or a series of sparks will pass from one to the other. This phenomenon and others associated with it are most readily studied by the use of an electrical machine or an induction coil, between the electrodes of which a great difference of potential can be easily produced. ”

“ The process of reasoning by which we discover such laws is called induction. As we can seldom be sure that we have apprehended all the related facts, it is clear that our inductions must generally be incomplete. ”

“ Let represent the weight of the hydrogen evolved by unit current in unit time, and the chemical equivalent of one of the products of electrolysis in the cell. Then represents the weight of that product evolved by unit current in unit time, and represents the current that will evolve unit weight in unit time. Now the electrolytes are prepared so that the weights of the constituents in the cells are given by where is a number which is the same for all the cells. ”

“ Two platinum electrodes are immersed in water slightly acidulated with sulphuric acid, and tubes are arranged above them so that the gases evolved can be collected separately. When the current is passing, bubbles of gas appear on the electrodes. When they are collected and examined, the gas which appears at the anode is found to be oxygen, and that which appears at the cathode to be hydrogen. The quantities evolved are in the proportion to form water. ”

“ The discharge seems to be independent of the position of the positive electrode, and to take place in nearly straight lines, which start normally from the negative electrode. If two negative electrodes be fixed in the tube, the discharge from one seems to be deflected by the other, and two discharges which meet at right angles seem to deflect one another.
If the discharge from a flat electrode be made to fall upon a body which can be moved, such as a glass film, or the vane of a light wheel, mechanical motions will be set up. ”

“ Natural Science makes us acquainted with the properties of bodies, and with the changes, or phenomena, which result from their mutual actions. It is therefore conveniently divided into two principal sections,—Natural History and Natural Philosophy. ”

“ In a crystal of Iceland spar the conductivity is greatest in the direction of the axis of symmetry, and equal in all directions in a plane at right angles to that axis.
181. Conductivity of Non-homogeneous Solids.—De la Rive and De Candolle were the first to show that wood conducts heat better in the direction of the fibres than at right angles to them. Tyndall, by experimenting upon cubes cut from wood, has shown that the conductivity has a maximum value parallel to the fibres, a minimum value at right angles to the fibres and parallel to the annual layers. ”

“ Water is often heated in a reservoir at a distance from the source of heat by the circulation produced in pipes leading to the source of heat and back. The winds and the great currents of the ocean are convection currents. ”

“ The sense of touch will enable one to decide with great nicety when the screw is turned far enough. If, now, we note the reading of the divided scale and also that of the divided head, and then raise the screw, by turning it backward, so that the given curved surface may exactly coincide with the four points, we can compute the radius of curvature from the difference of the two readings and the known length of the side of the triangle formed by the points of the tripod.
5. Unit of Time.— The unit of time is the mean time second, which is the of a mean solar day. ”

“ If the colder surface of the wall be exposed to air of temperature to which the heat which traverses it is given up, will be greater than The difference will depend upon the quantity of heat which flows, and upon the facility with which the surface parts with heat. ”

“ The Electric Arc.—If the terminals of an electric circuit, in which is an electromotive force of forty or more volts, be formed of carbon rods, a brilliant and permanent luminous are will appear between the ends of the rods if they be touched together and then withdrawn a short distance from each other. ”

“ No indubitable evidence has as yet been given that it can be refracted, or that it exhibits the phenomena of interference, diffraction, or polarization. When it falls upon an electrified body the charge on the body gradually disappears, the effect being to render the air or other gas surrounding the body a conductor. ”

“ The screw runs in a nut in the second piece, which has a vernier attached, and carries a horizontal telescope furnished with cross-hairs. The telescope having been made accurately horizontal by means of a delicate level, the cross-hairs are made to cover one of the two points, the difference of level between which is sought, and the reading upon the scale is taken; the fixed piece is then undamped, and the telescope raised or lowered until the second point is covered by the cross-hairs, and the scale reading is again taken. The difference of scale reading is the difference of level sought. ”

“ After the rarefaction has reached a certain point the discharge ceases to pass as a spark, and becomes apparently continuous. The arrangement in which this discharge is studied consists of a glass tube into which are sealed two platinum or, preferably, aluminium wires to serve as electrodes, and from which the air is removed to any required degree of exhaustion by an air-pump. Such an arrangement is usually called a vacuum-tube. ”

“ If the screw be turned through revolutions, as shown by the scale, and through an additional fraction, as shown by the divided circle, it will pass through times the pitch of the screw, and an additional fraction of the pitch determined by the ratio of the number of divisions read from 0 on the divided circle to the whole number into which it is divided. ”

“ Convection.—If a vessel containing any fluid be heated at the bottom, the bottom layers become less dense than those above, producing a condition of instability. The lighter portions of the fluid rise, and the heavier portions from above, coming to the bottom, are in their turn heated. ”

“ It penetrates all substances and is partly obstructed by all substances, the obstruction being greater as the density of the substance is greater. It is apparently capable of true reflection to a very small degree. ”

“ The carbon forming the positive terminal is hotter than the other. Both the carbons are gradually oxidized, the loss of the positive terminal being about twice as great as that of the negative. The arc is, however, not due to combustion, since it can be formed in a vacuum. ”

“ Cells of this sort, which have been constructed directly by coating lead plates with the proper oxides of lead, are called storage cells. They may be put in condition for use by sending a current through them in the proper direction. The sulphate of lead formed plays an important part in the operation of these cells. ”