It has been found in relation to galvanic batteries that the wear and tear takes place during that period in which the circuit of the cell is completed; and in theory, if the plates are properly amalgamated, they are not effected by mere immersion in the exciting fluid, but in practice it is always better to remove them when the battery is no longer required; more especially is this found of advantage with those batteries in which a solution of the bichromate of potash is used. In any case when the amalgamation on the surface of a zinc plate becomes imperfect, the two metals (mercury and zinc) are inclined to form "surface circuits" on the plate itself, and by this setting up of minute currents between various points, rot only gradually decompose the plate, but, what is of far more importance, seriously weaken the individual action of the cell. It is a law worth remembering, that, when in use, the power of a battery made up of a given number of cells is equal to the sum of such a number of the weakest cell in the circuit.

To effect the removal of the plates, which, if left to the memory of an attendant, might often be forgotten, Mr. Barker placed the jars containing the liquid on the top of a wind reservoir supplied from the main bellows, and suspended the plates in a frame above. When the bellows are blown the reservoir becomes inflated, raising the cells so as to immerse the plates; when the wind ceases the reservoir gradually collapses and the jars sink down, leaving the suspended plates high and dry. The battery is not placed within the console, or of necessity in any particular portion of the instrument, but wherever it is convenient-generally in or near the organ itself.

It may be well to mention that the usual form of battery employed is simple, inexpensive, and easily replenished from time to time with the necessary ingredients by any careful person. It does not require attention more than four or five times a year at the most. Those who are ignorant on the subject are apt to imagine that electricity is a treacherous or uncertain agent, but it is obvious that chemicals of equal quality, under given and similar conditions, must render like results in their actions. Notice of any falling off in the battery power is given by means of a galvanometer placed in the console for this purpose. At the same time it shows whether or not the wind is in the organ, as indicated by the immersion of the plates. Thunderstorms or other atmospheric conditions in no way affect the action of an electric organ, as earth currents are never utilised as in telegraphy.

It will be noticed that in the electric key action two intermediate agents are employed, to make the depression of the key open the pallet in the sound-board, viz., electricity and pneumatics, and it might be with reason supposed that such a complication would tend to produce a slowness or

delay in operation. This has not been found the case in practice. The electric current takes no time that the senses can appreciate in going even miles, and in the short circuit employed in organs electricity performs its work simultaneously with contact being made at the key. The pneumatic power-bellows, unlike those used in a mechanical organ, where they must be of sufficient size to pull open several pallets at once, to say nothing of having to move long trains of action, are now only required of a power to open one pallet, and are therefore reduced to such a size that very little compressed air is enough to inflate them; moreover their small and sensitive valves are in no way impeded by mechanical attachments. The practical result of this is that no perceptible difference of time can be discovered between the depression of the key and the speech of the pipe. This is proved beyond all doubt by the excellent repetition touch which is invariably obtained when the electric action is properly constructed, for in this respect it not only equals but far surpasses any mechanical action whatever.

In most cases where organs already built are to be reconstructed on the electric system, it has been found advisable to apply externally a pneumatic power-bellows beneath each original pallet, similar to Mr. Barker's arrangement, but placed in tiers, so as to get them in the same length as the sound-board. These are worked by the exhaust system, attenuated air being used instead of pressure, for the following reasons: The ribs or sides of pneumatic power bellows, if not made very rigid and lined with cardboard, are subject to being overstrained and inverted when they are inflated, and thus either permanently locked, open, or destroyed. If they are made of a rigidity that secures them from this defect, they are not sufficiently free in their action in the treble or smaller size. By the use of exhaust in lieu of pressure, no stiffening of the ribs is necessary, the cost of manufacture is reduced, and at the same time greater durability and freedom from noise is attained. In the conversion of organs to the electric system, all the existing mechanical action, being useless, is set aside, and consequently under these circumstances the expense is greater in proportion than where a new instrument is provided. The cost of this action must necessarily exceed that of ordinary construction, unless similar conditions are imposed, in which case comparison will be doubly favourable, when the addition of the more valuable and imperishable materials employed is taken into consideration.

CHAPTER IX.

The Draw-stop Action-Commutation Pedals.

THE term "draw-stop action" is given to that mechanism which regulates the movement of the sliders, and thus commands the various stops or ranks of pipes on the sound-board. It, therefore, is necessarily situated between the claviers and the ends of the sound-boards. It may be either purely mechanical, pneumatic, electric, or composite in its construction. Properly speaking, the composition pedals come under this head, as they also command the sliders collectively.

In all modern organs the knobs which control the stops are placed within easy reach of the performer, and in the larger instruments they are usually situated on either side, arranged in sets relating to the various departments on which they act, the couplers, or those connected with mechanical combination movements, being on the left.

The earlier organs had no draw-stop action. This addition to the instrument was made in the sixteenth century, and it is only within the last hundred years that there has been any recognised method of bringing all the knobs of the various departments together, and within easy reach of the player.

The exigencies of position, space, &c., tend to make the mechanical form of this action assume various individualities in different organs, but there are important principles which characterise more or less every specimen. The usual forms come under one of two great divisions—viz., the wooden trundle action or the iron trundle action. In the making and arranging of these the relative positions of the claviers and the sliders must be taken into account. The one most frequently assumed is that in which the great organ sound-board is immediately behind the front show pipes. It is quite immaterial at which side of the sliders the action is attached, and in small organs of one manual it is generally arranged that half are on one side and half on the other.

Presuming the position above described to be taken, Fig. 36 gives an illustration of the wooden-trundle arrangement. Starting from the end

nearer the claviers, K is the draw-stop knob, appearing at the consol, on the ivory face of which is engraved the name given to the particular set of pipes it commands. R is the drawstop rod, to which the knob is attached. This rod may be of great length or only a foot or so, according to the distance of the trundle from the manuals. Draw-stop rods are usually about an inch thick, whether round or square, which is a matter of taste. The end of the rod is mortised to receive the arm A, which is kept in position by a small iron pin. This arm is fixed at right angles to one side of the trundle T. The trundles are square, and are made of

stout wood, thoroughly seasoned, for were these to warp, the sliders would be inaccurately drawn or closed.

Each trundle rotates on iron spindles fixed to it at either end, which move in framework suitably placed to receive them. Another arm, a, communicates with the trace c, by means of a mortise and pin. The trace is made of pine, and reaches from the second arm to the lower end of the lever L, to which it also is mortised. The lever is of beech, oak, or some other hard wood, and is hung on a centre about a third from its upper extremity. The upper end of the lever is fitted into a hole in the slider; the trundle arms A, a, have no actually fixed positions, though the first is always placed as nearly on a line with the rod as possible, and the

second in a like position to the lever; these arms are occasionally made of iron.

The action of this arrangement is easily understood. When it is desired to bring a given stop into play, the knob K is drawn forward, which, of course, brings with it the rod R. The rod pulls the trundle arm A in the same direction, and the trundle T revolves on its axis a quarter of a turn, causing the arm a to draw the trace c from right to left. This acts on the lever L, the lower end of which goes inwards, whilst the upper end in its outward course takes the slider with it. The reverse of this would silence a stop already in use.

In the iron trundle draw-stop action, the trundle and arms are made of wrought iron instead of wood (Fig. 37 shows this arrangement). The trundle T is placed at the edge of the sound-board and not under it, as in

U

7

FIG. 37. THE IRON TRUNDLE ACTION.

the wooden-trundle action. The upper end u is above the level of the bottom of the sound-board. The trace is entirely dispensed with by making the bottom arm A much longer, so as to reach from the draw-stop rod B to the trundle. The top arm a is at the upper extremity of the trundle, in fact, may be termed a continuation thereof, and is made to incline towards the slider s, to which it is fixed by a bolt. On pulling forward the knob K the trundle is turned as in the first case, and acting immediately on the upper arm the slider is drawn out.

There is another action for commanding the stops, patented by Messrs. Herbert and Beale, called the "commutation pedal movement,, which has been applied to small one manual chamber organs with great advantage. The stops are in this arrangement acted on by pedals, which on being pressed alter their position, whatever that may be. Thus, suppose in an open diapason the slide is in and the stop silent, pressure on the pedal at once brings the slide out and renders the stop available;