We will now, before we go any further, look at the Wimshurst itself and give some account of the results of small improvements that have been made. First of all we look at the conductors. In the third machine brass was discarded and magnalium was substituted. As far as I am aware, magnalium had never before been used for this purpose. In passing it may be said that magnalium is an alloy of aluminum and mange-sium, and strange to say, is lighter than aluminum. It is a better conductor than brass. It takes a high polish, especially I have found with paraffine, and when once polished practically does not tarnish. It is very easily worked and is not expensive. It is a most useful metal.

The conductors consist of two magnalium tubes 1 3-16 in. diameter, and from these magnalium rods project carrying points to collect the electricity from the plates. There are, of course, brass balls at each end of the collectors. The jars consist of four gas jars. These are very convenient, having a length of 10 in., a diameter of 2 in., and a glass bottom of 3 in. They were mounted on sheet ebonite, and after being covered for 2 in. with tinfoil, strips of India rubber were glued over the bottoms and on to the ebonite, thus holding them firm. A wood plug inside covered with tinfoil carries a magnalium rod, which is so screwed into the conductors. The ebonite is mounted on a piece of wood, and this is made to slide in or out. This is of great use, as if anything goes wrong with the belts, the conductors can be instantly removed from the stand, and the belt at fault easi y got at.

Next, we may say a word about the brushes. These are generally made fixed, but we prefer two frames movable upon the axis that carries the plates. Although the machine develops the greatest power when the brushes are placed at " five minutes to five," yet when separated so that the frames are at right angles to each other the sparks are more frequent. Sometimes it happens that the machine does not readily sensitise; then moving the frames apart brings it on at once. We have made a simple arrangement by which the frames are maintained in any position. Two small pieces of wood, AA, are fixed by screws into the two frames; the two pieces join together at B where is a stout pin, which projects into a slot, 88. By means of two small nuts placed on each side of the pin at B, the frames can be clamped in any position. See Fig I.

The Brushes

Unless these are always in contact with the plates, there is great loss of power. To insure this the following arrangement has been made: A and B, Fig 2, are two thin pieces of wood. A band of leather unites them at C and forms a hinge. A piece of thin brass wire is rolled round a pen, and thus made into a light spring, which is inserted at SS.. The brushes are inserted • at D and D through holes drilled in the wood, and connected up by two wires to the frarce wire at C. By this arrangement the brushes

The Brushes 32

Fig. 1.

are always kept in close contact with the plates. For the single plates a thin piece of wood projects from the frame towards the plate, and on this is mounted a similar spring S, Fig. 2, the end of which is straight, and passes through a ring at L and, projecting outside carries the brush. It will be obvious that this in like manner is always pressed firmly but lightly against the plate.

The Brushes 33

Fig. 2.

A few general hints as to working may be useful. Dust and damp are the two great enemies to effective working. The removal of the first is a comparatively easy matter. A short stick round which a piece of soft rag is wrapped can be held between the plates while they are slowly turned. It is well from time to time also to clean the unsectored sides of the plates. The tinfoil sectors become black with use. We have substituted thin sectors of magnalium well polished; these can easily be cleaned from time to time as required with a little paraffine on a rag. But there is considerable difficulty in mounting them, and so they are liable to leak. We have tried capping them with small half-moon shaped pieces of ebonite, but with very doubtful results. Probably it will be possible to obtain some magnalium foil in time, when the difficulty of mounting will be overcome.

The Brushes 34

Fig. 3.

Getting the machine damp is a much more serious catastrophe, and at a thousand feet above the sea, with sudden changes of temperature and variable hydroscopic conditions, is almost unavoidable. It occasionally happens, in a sudden change from cold to warmth, that dew is precipitated on every piece of metal or glass in the house. The machine, though always kept covered up when not in use, naturally suffers. It rarely fails to sensitize, but there is no output, and if the room be now darkened a curious state of things is revealed. On each side, half the conductor is receiving positive, and the other half negative electricity. So that although the machine is alive with generated electricity, yet from the positive and negative being thus mixed up the output is nil. The only thing to do now is to go mathematically to work. Don't try mov-

The Brushes 35

Fig 4.

ing near the fire, for fear of the plates warping - a disaster which once occurred with a small machine. By the bye, it may be useful to add that the plate thus warped was successfully straightened by placing it between two warmed iron plates from the oven and putting weights upon it. Get warm cloths and go over all the plates. Warm the glass jars and rub them well with a warm cloth. A hot brick placed under the plates is sometimes successful, but the plates should be kept turning. The flame of a spirit-lamp passed rapidly backwards and forwards underneath the rotat-ing plates sometimes answers well. When once it is seen that all the collectors give brushes on one side, and points on the other in the darkened room, there is little probability of there being further trouble. Un-der the atmospheric conditions we have mentioned the machine is very liable to reverse, and the plates are best kept very slowly turning till the commencement of the work in hand.