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that I was obliged to use again the ball, and then the wire itself stuck to the edge of the lamina. Following, however, farther the idea of discharging the bead by its wire meeting with the smallest conducting mass possible, I thought of substituting for the brass lamina a single silver wire like that of the bead; and at last I thus succeeded. This is the part of the figure which I am going to describe.
The last alteration I found necessary to make in the apparatus, which is represented in the figure, not being made at that time, it must be supposed, for the present, that the piece 28 is represented by the lead slip 19, 19. The piece 23 is a brass spring of about half an inch in breadth, at the base 24, where passing under the bent part of an upright brass piece 25, it is thus fixed with the latter, by screws, on the base. The breadth of the spring 23 diminishes toward its end, where it is terminated by a brass wire bow 22; in this is stretched the thin silver wire 21, against which that of the bead comes to strike. The upright brass piece 25 has at the top a screw 26, pressing against the spring, and serving to produce small motions, backwards or forwards, of the horizontal wire 21, previously brought nearly to the proper distance, by moving the lead base 19, 19. The moment of the meeting of the two silver wires is to be an instant before the bead strikes the ball 18: then, by a jerk produced at the meeting of the wires, the sticking of the bead to the ball is effectually prevented.
This was only finished in the beginning of last April ; the strikings of the bead were then regular and uninterrupted, while there was no shake of the apparatus itself; but being on a table, I soon found, that by walking in the room, and also by the agitation of the air in opening and shutting the door, the motions of the bead were disturbed. This determined me to fix, against the side of the room which had a proper light, a glazed box, in which I placed the apparatus ; and I fixed under it, at its level, a little table, in order to place there additional columns, which became necessary to increase the power of the instrument.
This apparatus being at last ready for regular observations, I began the meteorological journal which I had in view, including, with the number of the strikings of the bead in a certain time and the observation of the barometer, the degrees of the thermometer and of my hygrometer in the room, the only place of which it could be supposed that the changes of the temperature and of the degree of moisture might affect the state of the column: I shall copy here the journal of these observations during the few days in which the fundamental column of 600 groups still acted alone, after which time I was obliged to increase the number of the groups.
2 P.M.... id. .....
4 P.M.... 30 ...... 56 ...... id. : ..... 12. ............ 30.1.. No striking the whole day.
This cessation of striking having lasted two days more, I judged that we were entering into the season when, in the two years before, the strikings of the gold leaves themselves had also ceased; so that in order to carry on the observations as long as possible towards the summer, it was necessary to increase the number of the groups This I undertook without changing the situation of the fundamental instrument, which, on account of the necessary steadiness and of being sheltered from currents of air, was to remain in the glazed box fixed against the side of the room. I made use therefore of the little table above mentioned for placing on it additional columns, which I made upright like the common pile, as more easily managed ; and knowing that with the same number of groups, the strikings would be accelerated by larger plates, but that it was a long and tedious operation to cut them round, I determined to make a column with square plates. For this purpose I bespoke some sheets of laminated zinc about the thickness of a card; but those which I received were so much puckered that I despaired of their being fit for my purpose ; however I obtained flat pieces of them by a method which it may be useful to explain.
I procured a good pair of hand-shears, and with these I first cut the puckered sheets into slips of one and a quarter inch breadth, as nearly as they could be traced upon such an uneven surface; and placing many of these slips upon one another between two pieces of hard wood, I pressed them with force in a vice, leaving them there for half an hour : they came out very flat, only not very straight, but this could be mended. Zinc, in this malleable state having nearly the softness of lead, stretches laterally by that great pressure, and thus the puckerings are effaced. Making then straight with a file one side of the slips, I marked on this edge with a divider,
points at one and a quarter inch distance ; and by these points I traced with a square the plates to be cut with the shears : these pieces were distorted by the cutting; but placing them also over one another, by scores, between two thick plates of brass, and pressing them strongly in the vice, they became flat ; and I had only to round a little the angles with a file, placing them again in the vice without the brass plate.
In this manner I made 300 zinc plates one inch and a quarter square, and having cut an equal number of pieces of Dutch-gilt paper of the same size, I mounted this upright column between four glass rods covered with sealing wax, fixed in a wooden base. This column, loose between the rods, is supported at the bottom on four insulating pillars one inch and a half high, on which is first laid a brass plate with a projecting part of about two inches, at the extremity of which is a large hole for receiving the end of proper conductors; and for the same purpose the column is terminated at the top by a similar plate, on which presses a screw in the common manner used for the pile. The top of this column, which is its positive extremity, was to be connected with the negative extremity of the horizontal column, and this required that the box containing the latter should be opened in front, I therefore placed only a pane of glass on the side where the bead hangs, in order to guard it against the motions of the air.
The first use which I made of this additional column with larger plates, was for the following experiments.
Experiment 16. Placing the negative (or lower) extremity of the column composed of the large square plates, in communication with the ground, I connected its positive extremity with a gold leaf electroscope, and after having observing the maximum, soon produced, of its divergence, I substituted for this column 300 of the small groups of the horizontal column, by placing the communication with the ground at its middle point : this produced the same divergence as the former, but it required more time.
I could not compare directly the effects of the two columns, with respect to the frequency of strikings of the bead, because at that time 300 groups of any size were no longer sufficient for producing them; but I compared the effects of the two columns for this purpose in the following manner.
Exp. 17. I first repeated the observation of the strikings with the horizontal column of 600 groups, its negative extremity being in communication with the ground : there were three strikings in five minutes. I then took off the communication of this column with the ground, and connecting its middle point with the positive extremity of the column of 300 groups of the square plates, I placed the negative extremity of the latter in communication with the ground. This was again 600 groups, but 300 of them were of larger plates, and there were then seven strikings in the same time ; and thus was confirmed what I had judged of the effect of larger plates for increasing the frequency of the strikings.
Exp. 18. I now connected the new column of 300 larger plates with the 600 groups of the horizontal column, leaving the communication with the ground at the negative extremity of the former.
This was in a more favourable moment ; for the addition of 300 of the small groups ought to have produced with the whole only eight and a half strikings in five minutes, and there were ten.
From this increase of power I expected a greater duration of observations in this season, but I soon saw a diminution in the frequency of the strikings, which disappointed me. I lost again much time in changing the arrangement of the apparatus, in order to take in also the two columns formed of tinned iron plates, mentioned in my first paper : there were 700 of these groups, which produced in the gold leaves nearly the same divergence as the column of 300 zinc plates one and a quarter inch square. This being the only change that I could undertake for the season, I began another course of observations; and it will be seen in the following journal how rapidly the effect went on diminishing.
30:19.. 11 .... 30.18.. M....
M.... id. ....... 11 ........ 29.75...... 66 ...... 39 .. no striking. 7 A.M.... 29•65...... 61 ...... 40
No striking the whole day. 7 A.M.... 29:6 ...... 64 ...... 402...... 1
or 1 in 10 min. 11 ........ 29•65...... 63 ...... 391...... 5
No striking in the evening.
Numb. of strik.
in 5 min.
Wave 17. 7 A.M.... 29.83...
40 ...... 10 ........
7 A.M.... 29.75.
39... no striking 4 P. M.... 30.2 ....... 65 ...... id. ...... 4
No striking in the evening
7 A.M.... 29.9 ...
.... 30.2 ...
No striking for a long time.
2 P.M.... 30•32....
103 ........ 30.28......
This great diminution in the frequency of the strikings made me think of connecting the ball 18 with the negative extremity of all the columns, in order to see what increase it would make in the frequency: but luckily at the same time it occurred to me, that, by producing a speedy manner of changing this connexion of the ball for that with the ground, and inversely, it would be a mode of discovering variations in the electric state of the latter, by comparing, in a short time, its effect on the strikings, with that of the negative extremity of the columns. This was the occasion of the last change which I made in the apparatus, as represented in the figure, which part I am now going to describe.
On the lead base 19, 19, I fixed two insulating pillars 27, 27, and on these a brass piece 28, at one extremity of which is fixed the ball 18, and at the other the machinery for moving the horizontal silver wire 21. By this insulation of the parts against which the bead and its silver wire come to strike, I can place them in a moment in