Gisbert Johann Eduard Kapp

“ Whether the one set of theorists or the other have come near a true explanation, or whether both are mistaken, is not a matter which need concern us; the important fact is that electrification is produced by the contact between two metals, and that the intensity of their electrification, or the force by which the two electricities are separated across the boundary line of the two surfaces, does not depend on the extent of the surface of contact, but only on the quality of metals used in the combination. The force is greater with some combinations and smaller with others. ”

“ We simply say that gravity is a force that acts at a distance, and since by direct experiment and astronomical observation it has been found possible to formulate a mathematical expression for this force, there is, from a purely practical point of view, no need to find an explanation of the machinery by which this force is transmitted through space, whether the space be quite empty or filled with other bodies. ”

“ Man has no sense by which he can estimate the strength of a current flowing in a wire—by touching the wire he may get a shock and thus conclude that the wire is at a higher potential than he is himself when standing on the earth ”

“ Thus, if an electric tramcar starting from rest attains its full speed of 24 miles per hour in the time of 20 seconds, its average acceleration is 1.2 miles per hour in each succeeding second, or "1.2 miles per hour per second." If instead of giving the speed in miles per hour we give it in metres per second, the acceleration of this car would be 0.535 metres per second per second. Taking the metre as the unit of length, the second as the unit of time, and the kilogram as the unit of force, we have thereby also settled what the unit of mass must be. ”

“ In comparison with this the e.m.f. of contact is very small, and that produced in a frictional machine is prodigiously large. The latter may easily reach tens of thousands or even hundreds of thousands of volts, whilst the e.m.f., under which lightning flashes occur, may be many millions of volts. Between the process of producing electrification by friction and producing it by contact, there is thus an enormous difference in degree, but no difference in kind, both processes being simply directed to the separation and isolation of charges of different sign. ”

“ If thickness has nothing to do with the capacity, then by reducing it to nothing at all we should not alter the capacity. In other words, the body which holds a charge need not be a conductor at all. Its conducting property is only necessary to let the charge distribute itself over the whole of its surface, in fact to get a charge on to it at all. If, however, the charge is not transferred to the surface from outside, but actually produced on the surface, then there is no need that the surface should be the surface of a conductor. ”

“ The units as regards length, time and force may be the same in all cases, but the units in which we express the amount of active matter producing the force must naturally be different in each case. We have also seen that the nature of the medium across which the force acts is immaterial in the case of gravitation, but may modify the force in the case of electricity and magnetism. Let us now, without for the moment specifying any particular kind of active matter, assume that one of the bodies contains a large amount of active matter, say units, and that the other contains one unit only. ”

“ Whilst approaching the uncharged, or weakly negatively charged, cylinder to the sphere we receive energy. There is attraction, because the negative end which is attracted is always nearer than the positive end which is repelled. After the cylinder has been discharged to earth there remains only attraction, and against this attractive force the cylinder has to be pulled away. Here our hand is called upon to impart energy to the system. We electrify the third conductor by the expenditure of energy, that is, by mechanical means. ”

“ There is an advantage in producing a high temperature in the filament of the incandescent lamp, but there is no advantage whatever in producing heat in the wires that carry the current to the lamp. On the contrary, there is an objection to it; not only does the generation of heat mean a dissipation of energy, that is, of something which costs money, but it may be a positive danger, since a conductor becoming red-hot may set fire to a building. ”

“ If we wish it to go on further we must increase the source from which the negative charge of the cylinder is derived, that is, we must charge the sphere more strongly. How are we to increase this positive charge? The most obvious thing is to increase it also by mechanical means, much in the same way as we increase the charge on the third conductor, and this is the principle on which the modern electric machines, the so-called "influence machines," work. ”

“ Everyday experience has so familiarised us with the action of gravity that we have become accustomed to simply accepting it as a fact in nature, without further inquiry as to the machinery which is instrumental in the transmission of this force through the intervening space. ”

“ If this medium is air, the force is greatest; if it is an insulator such as oil, glass, mica or paper, it is times smaller. This means that to bring a unit of positive charge to our sphere through such a medium takes times less energy than to bring it through air. In other words, to obtain the same charge an e.m.f. times smaller is sufficient, or, if the e.m.f. is the same, the resulting charge will be times larger. Hence by using a dielectric other than air the capacity of our condenser is increased times. ”

“ What precisely takes place we do not know, but as a matter of convenience we assume that there is only one current, namely, that which flows from the positive to the negative conductor, much in the same way as water will always flow from the higher to the lower level.
Electricity, being an imponderable entity (in reality merely a form of energy) , cannot be connected mentally with any conception of level, such as is legitimate in the study of the movement of heavy bodies. ”

“ The astronomical problem is exceedingly complicated because of disturbances from other active masses for which allowance has to be made, but in studying the same problem as applied to electric charges no such complication need arise. We can so devise the conditions of the experiment that no other force than that acting between the large and the small body is present. ”

“ We do not know what electricity is any more than we know what magnetism is; all we know is that they are not of the nature of ponderable masses, and that under certain circumstances they may become the vehicle for the transmission of energy in a similar manner to the ether itself. We might, in fact, consider them as ethereal manifestations without any attempt to explain the exact nature and mechanism of these manifestations. Such a conception is quite compatible with the practical use of our general formula ”

“ The potential difference between any point of the wall and the surface of the sphere is numerically equal to the energy required to bring a unit of positive electricity from the wall to the sphere. The wall of the room being in contact with the earth, both must be considered as at the same potential, and if we arbitrarily fix this as zero (which is evidently permissible since we deal with potential differences and may take our datum line where we like) , then the energy expended is the absolute potential of the sphere. ”

“ A wooden sphere covered with the thinnest layer of gold-beater's skin will at the same potential hold exactly the same quantity of electricity as if it were made of solid brass or lead or any other metal. Electricity at rest resides entirely on the outside of a metal conductor. We might reduce the thickness of a shell to any degree, and still the charge is not altered. ”

“ This law that the potential at any point inside a conductor is the same as the potential on its surface, may also be proved without the aid of mathematics by the following reasoning: Imagine a conductor of any shape, and assume it at first to be solid right through. No free electricity could possibly remain in the substance of the metal, since the mutual repulsion of all the elementary charges would cause these to try to move apart as far as they can. ”

“ The same reasoning as above applied to electric attraction and repulsion may also be applied to forces produced by magnetism, but if we attempt an experimental verification of the general law of forces acting through space we encounter some difficulty. When dealing with electricity it is quite easy to isolate a positive from a negative charge each on its own conductor, or, as we may also term it, it is possible to accumulate free electricity of one sign on a conductor. It is not possible to accumulate only north magnetic matter, or only south magnetic matter on one piece of steel. ”

“ It should be noted that the term "active mass" is merely conventional as far as electricity or magnetism is concerned. It is not to be taken in its literal sense as applying to something which has bulk and weight. A steel bar, after being magnetised, weighs exactly the same as before, yet its ends exhibit certain properties which we may conventionally ascribe to accumulations of magnetic matter which, if brought near magnetic matter adhering to the end of some other magnetised bar, becomes "active matter" in the sense of producing either attraction or repulsion. ”

“ At first, it is easy enough to push electricity on to the sphere, because there is only a little quantity there which repels the influx of new units, but as the charge proceeds the quantity accumulated grows, the potential grows, and it requires more and more energy to bring every single unit on to the sphere. Finally, a point is reached when the pushing force of the machine, or, as we term it technically, its electromotive force, is just able to balance the repelling force of the charge accumulated, but not able to add a single unit. ”

“ In every point of the space surrounding such a conductor, there acts a force pushing positive electricity one way and negative electricity the opposite way. If the charged body is positively electrified, the potential will be positive all around it, but higher close to the body and lower the farther we recede from it. We must conceive a charge as a something which is adhering to a conducting surface; where there is no conductor there can be no charge, though there may be potential. ”

“ It will be observed that the segments of both discs, whilst passing each other on the horizontal diameter, are charged with electricity of the same sign, namely, positive on the left and negative on the right.
If we now inquire as to the true cause of electrification, we find that apart from the quite insignificant initial charge on A and B, it is simply the mechanical energy required to produce rotation against the opposing force of electrostatic attraction between the outer and inner segments. A has a positive, and a has a negative charge. ”

“ We have strengthened the tubes of force passing from sphere to cylinder. The total flux emanating from the sphere has not altered, for that is strictly limited by the charge originally on the sphere, but whilst with a sphere free in space the flux is evenly distributed all round, we have, by bringing the cylinder near, and especially by discharging its positive electricity to earth, disturbed the symmetrical field of the sphere, making it much denser on its left half, and thus increased the inductive effect on the cylinder. ”

“ Under certain conditions the force of attraction may be sufficiently great and the distance sufficiently small to cause electricity to leap across the intervening space, and then we have the familiar phenomenon of an electric spark. ”

“ Once we assume the existence of this physical though imponderable, that is, weightless substance, we may regard it as instrumental not only in the transmission of gravitational forces, but also of electric and magnetic forces and as the carrier of light and heat rays. There is, indeed, very strong experimental evidence that light, electricity, magnetism and all other manifestations of energy are propagated by ether vibrations. ”

“ If the surface is quite plane the repelling force between the elementary particles of the charge is parallel to the surface, and there is no component tending to flake electricity off the surface and disperse it into the air. If the surface is curved there is such a component, and it becomes the greater the more sharply the surface is curved. At a sharp corner it becomes very great, and if the corner is drawn out into a sharp point the force is so great that all the charge is dissipated as soon as brought to the conductor. ”