apparatus employed in the course of them, it being for the most part new, and so constructed as to insure as far as possible much precision, leaving more minute details to the accompanying drawings.

2. The electrical machine, fig. 1, consists of a circular plate of glass, three feet in diameter, mounted on an axis, between two horizontal supporters of mahogany; these are sustained by four vertical columns, of the same wood, fixed on a firm base. The rubbers are insulated on pillars of glass, (a) (b) and are placed at each extremity of a horizontal diameter of the plate. The positive conductor (c b d) projects in a vertical position, in front of the plate; whilst the negative conductor (aeb) passes in a curvilinear direction behind it and connects the rubbers of each side. The whole machine is sustained by four short legs, (mno p) on a steady frame, (no) furnished with rollers; and also with three levelling screws, (h o p) so that it may be easily moved into any required position; and may be eventually so adjusted and fixed, that the axis of the plate, which has free motion backwards and forwards in the holes, in which it turns, may not tend more to one side than the other, and produce an unequal action on the rubbers.

The plate is turned by means of an insulated handle, immediately in front of which, there is a short index, fixed in the axis, which travels over a divided circle, (1) attached to the horizontal part of the frame, and through the centre of which the axis passes; thus, the number of revolutions of the plate may be accurately estimated.

The centre of the plate, is strengthened by two smaller plates of glass, cemented to each side by varnish; and there is a small stop inserted into the axis, to prevent the pressure from increasing beyond a certain point.

The conductors, when the machine is employed to accumu

late a charge, are of as small an extent as possible, and are covered, except at the receiving points, with sealing wax. The positive conductor being in this case constructed of small straight tubes, as represented in fig. 2; and its extremities terminate in balls of varnished wood, through the substance of which the necessary metallic communications pass.

*

3. The requisite accumulation is obtained by means of coated jars, which are employed either detached or collectively; they are not furnished with covers, but the charge is conveyed directly to the bottom of each jar, by means of copper tubes, three-eights of an inch in diameter; these terminate above in balls of baked wood, and are supported below by a convenient foot, firmly cemented to the bottom of the jar; which is previously covered with a circle of pasted paper, leaving a central portion of the coating free, for the perfect contact of the charging rod, which passes through the center of the foot, as indicated by the dotted lines in fig. 7.

These jars, when employed either separately or collectively, are placed on a conducting base, sustained by short columns of glass, or some other insulating substance, so that the whole

* This machine was constructed in the year 1824; I had previously seen one on a similar principle, by Mr. Eagland, a Surgical Mechanician of considerable ability, residing in Poland-street, London. In Mr. Eagland's machine, the same frame which sustains the plate also carries the rubbers in the usual away, but it is thrown into a horizontal position, the whole being insulated and supported by four long glass columns. The negative conductor passes in front under one of the arms of the positive conductor.

Mr. Eagland's machine has very great power, and is an immense improvement on those of the ordinary kind. The great advantage obtained by the present arrangement, is stability; the requisite insulating pillars being relieved from the weight and straining of the framed plate, when in action: the conductors are advantageously placed, and the axis of the plate can be accurately adjusted, which is of great importance in obtaining a steady and equal excitation. The whole arrangement will be found very desirable and extremely convenient in practice.

can be insulated when required; and for the purpose of allowing them to be charged and discharged with precision; they are connected with what may be considered as two centres of action; the first of these consists of a brass ball, (a, figs. 3. 14. 16) which slides with friction on a metallic rod, (c d) so as to admit of its being adjusted to any required altitude; it it has a number of small holes, drilled in its circumference for receiving the points of the connecting rods of the jars-The rod which sustains this ball, is either insulated on a separate foot, and connected with the conductor of the machine, as in fig. 16; or is otherwise inserted directly into it, as in fig. 14. The second centre, consists of a larger ball of metal, (b) attached to a firm foot, and placed on the same conducting base with the jars, so as to have a perfect connection with it. The wire (nb fig. 14) employed to transmit the explosion, terminates in this ball.

When it is required to give the first centre of action (a) fig. 3. a separate insulation, the insulating rod of glass, is screwed immediately into the lower ball; (b) and sustains the metallic rod above described, by the intervention of a ball of baked wood, (d) as seen in figs. 3 and 16; the opposite extremity of the rod terminates in a similar ball, (c) through the substance of which, the conducting communication with the machine passes when it is placed on a separate foot. All the metallic connections are covered with sealing wax, except at the points of junction; and the wood balls and different insulations are carefully varnished.

4. To transmit the explosion at any required period, two different methods were employed, according to the circumstances of the experiment-In the first, the discharge is effected by means of the instrument represented in fig. 4. There are two balls of brass (a) (b) placed one over the

* Rosin or brimstone answers very well for this purpose; the latter is easily moulded to any convenient form, by pouring it in a state of fusion into common drinking glasses.