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By JOHN T. SPRAGUE ("SIGMA.")

PROPOSE to show now that the hydraulic circuit can furnish us with illustrations of the actions which go on in the electric circuit during the variable period; but I must ask for intelligent consideration of the principles at work; and the recognition that an analogy is not identity; that it is like a fable or parable, which teaches us truths under forms which might be even nonsensical if treated literally.

M

FIG. 7.

51. Let us consider more closely what goes | pressure, or wound into a double helix, like on in the elastic pipe. Fig. 8 will help us. the electric conductors in Fig. 5, p. 371, one The cross-barred cone I is intended to repre- connected to the source, the other closed on sent the inertia of the water in the pipe, its working turbine. When pressure is put resisting the pressure of the source, shown by the entering arrows; the elastic pipe yields, expands into the curve G, which gradually advances along the pipe; a similar but reverse action and curve occur at the other side of the source. We have the strong local current in the source with no current in the conductor, till the stress is distributed along the whole length. We have, in fact, the most perfect analogy to the known action of the electric cable in the tank.

FIG. 8.

No one has ever been so bold as to deny that the hydraulic circuit gives an almost perfect analogy to the electric circuit, while steady current is passing. I used it myself in these pages over twenty years ago, in a form which I also employed in my "Electricity," and others had seen the use of this analogy more or less clearly at a still earlier date. But the conditions of the variable periods, the absorbtion and re-issue of energy in inductance and magnetance, are not so readily covered by this analogy. I have already explained why this is so-viz., We have something more; it is obvious upon one, the primary, converting it inte that practical hydraulic circuits have no elasticity, while inductance and magnetance that the advancing current is a purely the taper form, will not a reverse taper form are, so far as merely mechanical conditions" skin current, which takes time to penetrate be produced in the other, the secondary, are concerned, perfectly analogous to the into the interior of the conductor. If the with a momentary "induced current" in it? effects of an elastic medium, which has to be reader turns back to § 35 he will see that If we set up intermittent or alternating satisfied by the source of force and energy we have here the very conditions stated by currents in one, will not a succession of before the true conditions of current can be Sir W. Thomson as to starting currents: induced currents appear in the other, and "When the period is very small compared could not its turbine be made to do work by set up.. If, instead of a rigid steel pipe, we with 400 times the square of the smallest energy supplied laterally from the primary, conceive an elastic hydraulic conductor, we diameter, multiplied by its magnetic permea- and by it from the "source," in a circuit Are not these complete analogies with introduce just the very conditions which are bility and divided by its electric resistivity, wholly unconnected to the source? analogous to an electric circuit having in- the current is confined to an exceedingly ductance and magnetance. Let us now con- thin stratum of the conductors." Substitute what we know happens as fact in the electric sider what would happen if the conductor C the elasticity of the pipe for magnetic case, and why should we not acknowledge of Fig. 7 were a strong elastic pipe, in con- permeability and the inertia of the water for that the energy is transmitted in both cases tinuation of $46-48, p. 373, and consider- electric resistivity, and have we not the by the current-carrying conductor, without ing now the actions of the "variable complete explanation of the phenomena? whose agency it is certain that no transmisperiods" at starting and stopping current. It is mere wanton assumption to argue that sion can occur? 54. I may now give a résumé of the 50. The first effect of the source is to pro- the cause is the ingress of the energy into duce a pressure in one direction; a suction, the wire from the external medium which arguments and reply of Prof. Silvanus which may be considered as a - pressure, in produces current merely to waste itself. The Thompson. As neither he nor any one else the other. The ultimate result would be to more closely the subject is examined, the has a single particle of evidence to bring produce the tapering pipe indicated by the more clear it will become that these theorists forward showing transmission of energy by dotted line P, Fig. 7; but this would take cannot stop at the electric current; they the medium during steady current, he time. There is the inertia of the water to must inevitably apply their doctrine to all overcome, and the elasticity of the pipe transmissions of energy, and hold that the would take time to come into operation. hydraulic circuit, the shafting and belting of The first effect would be to suck water from machinery, do not transmit energy, but only e-side of the pipe and force it into the serve as waste pipes to some energy, worked side; while no current would be pro- off as frictional heat, in order to enable the duced in the pipe as a whole. There surrounding medium to transmit energy to would be a local current in the source the real work. 52. They are already on the threshold of entirely engaged in expanding the flexible pipe close to the source. Now this is exactly this preposterous absurdity. We have Mr. what happens with an electric circuit. If a Tolver Preston teaching that it is energy ether" which does all worklong submarine cable is coiled in a tank, a stored in the " current may be sent in at one end, and may to use his own words, "coal must be renot appear at the other end for two or more garded as a mere machine for extracting seconds-nay, several successive signals may energy from the ether"-and suggesting that be sent in before the first will issue, and they we ought to learn how to go on burning the will leave the cable in similar order and same coal for ever, an arrangement which time. I may observe that this is a crushing would soon settle the miners' eight-hour day fact for the new doctrines. If the energy question. He is arguing this in solemn travels via the medium in the small tank earnest, and how long will it be before he 55. However, he begins with the case of with the velocity of light, as asserted, it tells us that shafting and belting are merely has only the tank to traverse, and every- agents subordinate to the ether as the true where it is provided with the desired "sink," source and transmitter of energy, and how induction between two separate coils of wire parallel to each other, at first separate, then for the wire is everywhere close to it. The can the hypothetical electricians deny it? 53. Returning to our elastic pipe, it is evi- connected together in series to produce signal ought to be instantaneously transmitted. The "retardation" is intelligible dent that when the source ceases to transmit parallel currents, and thirdly so connected enough when we consider that the energy is current, the stress in the pipe will still pro-as to produce opposing currents, and shows the being continuously drained away into the pagate current till the pressure is equalised different qualities of extra spark and energy. This is just what we know I showed, in reply, that the whole facts are inductive and magnetic fields, and can only throughout. ordinary electro-magnetic ones; that the transmit current when these are fully happens in the electric "extra current." charged, after which they make no further But we can make the analogy still more mode of transfer of energy is not direct Let us conceive two elastic across the medium, but by the production claim, and steady current goes on unim- complete. pipes placed side by side and under suitable of magnetic lines of force traversing both peded.

VOL. LIII.-No. 1873.

adopts a logical dodge: he says, if I can show that there are cases in which we are compelled to admit that energy does traverse the medium, I am entitled to claim that it does, or may do so always. He then asks me if I have "any evidence of any case in which there is transference of energy which cannot be accounted for by the hypothesis of lateral transfer through the medium." Now this is thoroughly bad logic. My whole contention is that the hypothesis fails altogether to give any intelligible account of the facts; then as the only case in which there is apparent transmission-never from the source to the work, but always from one conductor to another-is by stresses due to starting and stopping actions, while all facts show that these stresses once set up, the medium has no further action, they can give no title to assert an unproved action during conditions wholly different.

ENGLISH MECHANIC AND WORLD OF SCIENCE: No. 1873.

coils, and the difference in the three cases is purely due to the different strength of magnetism produced; that if, in the first case of separate coils, identical in principle with my own illustration (Fig. 6) of an induction coil, we place the induced coil at right angles, there is no effect at all, simply because the air core and magnetic lines do not traverse it; but if we use an iron core traversing both coils, it is of no consequence what position the two coils take to each other, because the iron carries the lines of force produced by one into the other in any position, and produces the reaction current, which is part of the magnetic action.

57. Prof. Sil. Thompson next endeavoured to explain the direct distribution from the source to the wire during constant current. He gave four figures of closed curves inclosing spaces, composed of a series of battery cells connected by wires, towards which rays of energy are directed across the space from each separate zinc surface to corresponding parts of the wire. But these figures, as I pointed out, imaginary, and actually opposed to known are wholly fact. He showed that potential (which is energy) increases with the series of cells, thus proving a linear action within the conductive circuit, and then throws this known, proved fact aside to make the energy of each separate cell cross the space to its own apportioned wire. The figures look very pretty, because of regular form; but that would vanish if the circuits were made irregular, as they really are; and they leave out of sight the known fact that action is not confined to the inclosed space, but spreads in all directions around the conductor.

Prof. Silv. Thompson then proceeded to
that deductions might be drawn from them
criticise my arguments, by so stating them
quite different from their reasonable mean-
ing. It is a not uncommon mode of criticism,
but has the defect that it leaves the real
argument untouched. Then he converts my
analogy of the hydraulic circuit into an
identity, and says,
Are the copper conductors elastic? Do they
"What trifling this all is.
swell up or contract in order to produce the
stresses, induction of currents in neighbour-
effects of surface charge, external magnetic
ing wires, and the like?"

JULY 17, 1891.

longitudinal planes of electric stress, and (3) work for any but a professional. A breakthe two combined to produce equipotential down generally means a dangerous accident; radial lines by their intersections, along but the breakdown of a wheelbarrow would which it is asserted that energy could flow have no worse result than spilling the conwithout resistance. Now this may sound tents. very reasonable until we inquire how these should be made is ash for the framework and lines are first generated. We all know they elm for the sides. The wheel should have The material of which a barrow exist, and the commonsense explanation is felloes of ash and ash or oak spokes. The that they are built up from the wire out-axle should also be of ash, and for all parts wards, by influences and energy acting from this should be dry and well seasoned, or the the wire. But the new theory involves their joints will rapidly work loose. There are construction from outer space, and gives us two ways of making a wheelbarrow. In the no hint why the energy issuing from the one the sides and handles are sawn out of source "radiant in precisely the same sense two pieces of board of suitable thickness, 56. Other illustrations are given in a lines proceeding outwards from a centre, bottom piece are dovetailed, tenoned, or as light is radiant," that is to say, as radii, such as in Fig. 1, and a back, front, and Hertz explorer, and in a plate of copper" swirls round," as Prof. Thompson says, nailed between them, and sometimes the facing an electro-magnet. Now the whole and builds up a network of lines, crystallis-wheel is a solid bit of inch board cut to a of these cases disprove the position main- ing themselves upon the conductor, which, circular form, and hooped with iron to pretained by Prof. Thompson, who places him- we are told, carries no energy, does not vent splitting. Such a barrow is easy to self on the dangerous two stools. What he transmit even an impulse, and has no other construct, and serviceable; but it has two proves by his cases is that energy may be function than that of a waste-pipe. Does faults. The arms, being comparatively thin, transmitted from a primary conductor to a light ever "swirl round"? Does any motion are uncomfortable to the hands, and as they secondary conductor; but what he undertakes once set up ever swirl, unless some fresh are level with the top of the barrow, it is to maintain is that the conductor does not force acts on it? What is that force accord-very difficult to tip a load out of it. The convey, but only absorbs, energy, and that ing to the new theory? Now, that question first fault is remediable by attaching a the energy of the source goes by the medium no one has ever answered, and until it is piece to each side of the handles to increase only. This he actually gives up in his in- answered the new theories are mere idle their thickness, and rounding off the whole, stances, and shows the conductor emitting speculations, based upon nothing. and distributing energy, which must have reached it from the source. second fault cannot well be rectified; but so as to give a good grip to the hands. The despised, and it is generally made very deep such a barrow is not altogether to be and large, so as to serve for conveying dead leaves in autumn, and other dry material of more bulk than weight. I will, therefore, give a few brief directions for making it before proceeding with the more orthodox and, indeed, is the only stuff fit for this wheelwright's barrow. work. It is very tough, does not readily Elm is the best, unless a very cross-grained bit is selected, split, and is not difficult to plane and work, how far this goes to answer the line of argu- foot, will be very suitable for such a barrow. My readers must judge for themselves in Fig. 1, which is to a scale of lin. to the and this is easily avoided. The proportions ment I have adopted, or whether it fairly The board out of which the sides are cut represents the use I have made of the must, therefore, be 5ft. long, and is divided analogy. advocates of the new theory have not itself, 1ft. for the part which receives But this fact remains: the thus:-2ft. handles, 2ft. for the barrow offered a single fact in evidence, and cannot the wheel. make their doctrine agree with facts. They should be 15in. to 18in., which will be the avoid even the attempt to explain the asso- depth of the barrow, and the thickness in. The width of the board ciation of current with its magnetic and full when planed. This chemical functions. They loudly assert that suffice for the sides but the back and front substance will I suggested two experiments:-1. To set energy is radiant like light; the truth being and form substantial tenons, as will be the Hertz experiments prove that electric should be lin., to hold the nails securely, a vessel of bisulphide of carbon in the space, that they disprove that notion, for light described presently. and examine by polarised light what stresses issues as radii from one centre, while the shape, I have sketched the conventional form, are set up. If these imaginary lines of energy lines of the Hertz experiments require the which is as good as any, and provides the As regards the actual exist, they would become visible. But we dual origin, and are really the spreading bearings for the wheel. This should not be know that no such result stresses are really shown, but not across not lines at all. And, further, like every then bring the barrow level at a convenient curves of electric and magnetic induction, less in diameter than 18in. the liquid. They are those of magnetism, other fact, they prove that an action takes height for the hands. Fig. 1 will, I think, Short legs will at right angles to the plane of the space. place in space when an electric current is set make all this quite clear. 2. As the special features of the Hertz ex-up or stopped, and that during the interval represent the front board of inch stuff next periments is the use of reflectors to produce there is no trace of any action whatever in the handles. If it is 2ft. long at the top, and nodal points in the so-called waves, and as space; but we have abundant actions shown 21in. or 22in. below, it will give about the Fig. 2 will Dr. Lodge has recently shown that the in the conductor during that very interval, splay required, and it should be 18in. wide thinnest film of metal acts as a perfect screen and can trace the energy of the source in the centre, from which it is slightly or reflector, I asked Prof. Thompson to con-issuing from it. To conclude, the new rounded off both ways for appearance sake. ceive a thin wire (portion of one of his cir- theories are, cuits) inclosed in a shell to reflect these rays Words, idle words! "Vox et præterea nihil". of energy away. Now according to the new The tail-board is precisely similar, but not theory, the current in the wire and the heat so long. It may be 20in. at top, and 18in. produced by it are supplied by energy reat bottom, or thereabout. ceived from the medium, and I invited proof is a plan view, I have made the handles In Fig. 3, which that this imaginary supply being cut off, 24in. apart, the front board 21in., back there would be any less current, or any legs WHEELBARROWS, No garden can be about that usually given. board 17in. The total length is, as before, heat given off from the inclosed wire. Of 5ft. The general slope, it will be seen, is course, the thing has been done over and barrow of some kind to convey manure and the handles must be satisfactorily cultivated without a of course, to a great extent, optional, but Dimensions are, over again, and we know that no particle of a score of other necessaries. This, moreover, admit the body easily, and the entire difference results. But Prof. Thompson only is, to my mind, exactly such an article as an barrow should wide enough to he cannot make the experiment because amateur carpenter should construct for him- nor reflector is known. Dr. Lodge self. neither look be There is no real difficulty to balk A heavy barrow is as absurd as a heavy but anyhow, even an imper- him; the material is easy to obtain, and so farm-cart-a terrible and wholly unnecessary too small clumsy for real work. ht to stop out some of the long as the barrow is fairly strong it will waste of power on the animal doomed to tage of the argument was appearance. not much matter if it is a little rough in draw it. The timber used is frequently a ergy was able to enter the different to a cart or carriage, which, in spite barrow, inherited from my predecessor, Moreover, a barrow is very load by itself, and I have myself a stableres were given, showing of the excellent instructions which I have which is veritably a weight-for-age affair. nes around the wire, (2) sometimes read, cannot be considered fit I do a fair amount of gardening, but I

་།,。

says

occurs;

HOME CARPENTRY-GARDEN
IMPLEMENTS.

invariably leave that barrow for others. The service, and either the bushed hole should be dotted lines in Fig. 1 show the position of used, or an eye with a flat strap on each the front and back boards. The hinder one side, that can be secured by a small bolt or must slope to clear the 10in. wheel; but the two. The bushed hole is the simplest of all, front one is often placed upright. It is a and will last a long time. The wheel is fixed fixture in this kind of barrow, as it gives to its square axle by making the latter with greater strength to make it thus. The sides a shoulder, against which the wheel can are held together by it, although it is a good abut on one side; a wedge is then passed plan also to run an iron bar through the through a transverse mortise on the opposite sides at x, with a nut at one end, which will side, and driven far enough to hold the The bar passes wheel securely. The axle should be of ash. make this part quite secure. The bottom of inch stuff, with the edges as to fit nicely, is through the legs, which are fastened at the upper end by a nail or screw. The legs are slightly bevelled so cut out of 2in. stuff, sawn at an angle above, dropped in from the top, and the nails are like Fig. 3, to accommodate them to the driven into it through the sides. It should splay or spread of the side pieces. The tenons not be put on by being nailed to the sides at of Fig. 2 are generally left sufficiently long their bottom edges, because the weight of to admit of being secured by iron or wooden the load carried will tend to draw the nails. pins inserted transversely outside the It should also not be cut so small as to fall mortises on the side pieces. The wheel is quite to the bottom of the inside, but a good sawn out of a piece of elm, ash, or oak, the inch of the side boards should project below first by preference. It should be 2in. thick, it; also it may be noted that there is no as a thinner wheel cuts into the ground need to put more than a couple of good too easily in damp weather. There is no nails on each side. More will only tend to actual need of an iron hoop; but it adds to split off a length of wood from the lower the security by preventing splitting, which edge of the sides, and as the latter splay out may occur from the shrinking of the stuff in wards the bottom cannot possibly fall hot weather. A square hole is cut for the through, and very little is needed to secure axle, which should be 24in. thick where it it. Sometimes a couple of strips are nailed passes through the wheel. It can then be to the sides for it to rest on, and sometimes tapered off each way, and have an iron ferrule a couple of cross-bars are tenoned into the at each end to prevent splitting when the pins of iron are driven in. These are, of course, inserted from outside, while the axle is held in its place. It is as well to line the holes in the side pieces with brass or iron tubing: otherwise the pins will soon enlarge the holes considerably. Another plan is to cut off the side boards at a b, Fig. 1, and screw in two iron eyes to receive the axle pins, Fig. 5. One plan is about as good as the other. If, however, in. board is used it will be found barely thick enough to take a screwed eye sufficiently large to be of

sides. This is not required if the bottom is
an inch thick, as it will have sufficient
substance to hold good-sized nails. This
will suffice, I think, for the description of
the barrow in question, and it should not be
necessary to repeat cautions so often given
as to accurate fitting of the several parts.
In point of fact, this barrow should be as
easy to make as a common box.

We can now turn our attention to the
orthodox wheeelbarrow, which we may be
sure would not have replaced the simpler one
just described unless it had proved more

suitable for the work it was intended to
accomplish. For tipping its load the garden
barrow does not equal a navvy barrow used
in the construction of our railways; but it
will, nevertheless, do this much better than
the first described, and it will hold more, and
is altogether better suited to meet the require-
ments of the gardener. This barrow is built
up with a framework of ash, of which the
side pieces are sufficiently long to form
handles. The usual length is oft., and the
width of the front of the central or box part
is 2ft. But as the garden barrow has its
sides more nearly parallel, the handles are
not more than 2ft. 3in. or 2ft. 4in. apart at
their extremities. The frame-work may be
divided as before: handles 2ft., barrow 2ft.,
and 1ft. extending beyond to carry the bear-
ings of the wheel. Fig. 6 shows the general
plan of frame roughly to scale. The sides
are sawn out of ash plank 2in. thick and 3in.
wide, but they are subsequently stop-
chamfered to appear lighter. 1in. stuff
(when planed) will do; but it is better to
have it 3in. in the rough, which will work to
at least 13in. The mortises will, of course,
above and below each.
be cut in the width, and by the usual rule
they will be one-third of such width,
leaving lin.
The cross laths holding these side pieces
together are of 2in. stuff, 24in. to 3in. wide,
or if much heavy work is likely to be done
they may be of 3in. stuff; but 2in. will
generally serve the purpose, and as the
tenons are lin. thick only, not much is
gained in the way of actual strength by add-
ing to the thickness, since the strength of
anything is but the strength of its weakest
tenons are made to project beyond the sides
part-i.e., in this case the tenon.
for about an inch, and are usually channelled
or notched with a gouge to give a neat
finish. It being very essential that this
frame shall be out of winding, great care is

These