Journal of the Right Hon. Sir Joseph Banks/Appendix
APPENDIX
Electricity
25th October 1768, about five miles south of the line. My machine was made by Ramsden, and worked by a flat plate 8 inches in diameter. The phial used was 6½ inches in height and 5½ in diameter without the neck; the distance between the stopper and the coating, 3 inches, the stopper made of wood and fastened to the glass on the inside by a red cement (probably sealing-wax). The electrometer was divided into thirty parts of 1½ inch as nearly as possible. About nine in the morning the machine was set up, the day being rather cloudy, and the ship going between three and four knots.
When the plate was first turned round the cushions appeared to be damp, adhering to the glass so much that it was with difficulty made to move very slowly, although the cushions were screwed on as tightly as possible. After wiping them very well the plate was made to go round, and in about ten minutes electricity was excited, though but in a small degree; the motion of the ship and the shaking of the table, caused by turning the machine, made the electrometer (which was a very unsteady one) move backwards and forwards visibly, so that it was impossible to ascertain exactly at what distance it discharged the phial, it however was guessed to be about a line when at the greatest distance.
It continued to work in this manner about half an hour, in which time several attempts were made to give a shock, but they succeeded very badly, the shocks being very slight, though given with as much electricity as could be got into the phial. It then (having grown by degrees weaker and weaker) ceased to work entirely. Water was applied to the cushions, but without any effect: everything then was wiped and dried as well as could be done in our situation, the cushions being carried to the fire, but no electricity perceptible to the touch was communicated to the conductor. Whether any was excited on the surface of the plate we did not then observe. An amalgam of lead was then applied, causing a small amount of electricity, but much less than at first, and this very soon ceased also. From that time no electricity perceptible (except by Canton's electrometer) could be communicated to the conductor, though the machine was worked nearly an hour.
In the course of these experiments two things were observed, differing from the phenomena usually seen. First, the phial when filled with as much electricity as possible would not retain it more than a very few seconds, three or four by guess (for no opportunity of measuring by a watch was given, the machine stopping work without any warning); at the end of this time not the smallest quantity of electricity was left, though I tried all my five phials. Two of these phials were such as were described above; the others were smaller, made much in the same manner, but instead of being coated on the inside were filled with leaf-gold. Secondly, the floor of the cabin in which the experiments were tried was covered with a red floor-cloth of painted canvas that had been issued to the ship from His Majesty's stores at Deptford. This was usually washed with salt water every morning and allowed to dry without being taken up. This proved as good a conductor of electricity as any we could make use of, so that a man standing on one side the machine and touching the coating of the phial was shocked by another who touched the conductor, without having any other communication with the first than by the floor-cloth under his feet. Dr. Solander and myself tried this in several ways, and made more experiments afterwards with Mr. Green's machine, as noticed further on.
The ill success of these experiments seems to me to have arisen chiefly from the uncommon dampness of the circumambient air, which had been observed by everybody since we crossed the tropic, and is fully noticed in my journal. By this solution alone can all the phenomena that appeared be accounted for.
Air charged with particles of damp is well known to be of all others the greatest enemy to electricity. It immediately attracts and dissipates all the electrical matter which is collected by the machine, which therefore worked faintly for a little while, till the damp was condensed on the conductor, and chiefly on the surface of the glass phial, and then ceased entirely. A small quantity was, however, always noticeable upon the surface of the plate, even to the end of the conductor.
The phial, though charged as full as the machine would fill it, even at the time of its best working, scarcely retained the electrical matter at all, owing doubtless to the communication made by the condensed damp between the coating and the stopper of the phial; this increased every moment, so that at last it would not contain any electricity.
The situation on board ship would not allow the use of a fire to warm the whole machine, which should have been done, and which would have been a great satisfaction, but the motion of the ship, the distance of the galley from the cabin, and the number of people who are constantly busy there, made that impossible.
The dampness of the air complained of here has not been observed now for the first time. Piso, in his account of the Brazils, mentioned it, and says that victuals which have kept well before spoil immediately there. This therefore may account for the general opinion of electrical machines failing to work when near the line, as the fault could not be in my machine which worked remarkably well in London, and fully as well as I expected in Madeira.
25th October 1768, 17 miles south of the line—Mr. Green's machine. This was made by Watkins: the jar was of glass 8 inches high and 7 deep, coated with varnish between the lead and the stopper, which was of cork, no varnish coming between that and the neck. The electrometer was divided into thirty parts of 1⅛ inch.
The plate at first refused to go round, as mine had done before, the cushions being drawn together by the glass, to which they seemed to adhere, probably from their dampness. After some time, however, this went off, and in about ten minutes electricity was excited.
The electrometer was then applied and went off at 7.
2. Electricity was kept in the phial thirty seconds without any appreciable quantity being lost.
3. A hole was struck through two cards by the discharging wire.
4. Much greater shocks were given to several people than any that could be given by my machine.
5. The phenomenon of the floor-cloth proving a conductor was tried more fully than before. A wire (b, see 
figure) was passed through the phial (a), the two ends of which were taken hold of by two people (c c), who each took hold of another person (d d); the operator (e) then touched the phial with his discharging wire, and received the shock through both arms, as did (c c) and (d d). Sometimes, however, the others (d d) felt it only in the arm by which they held (c c). The comparative force of the blows which each felt were difficult to ascertain, but we supposed that (c c) felt more than (d d), and probably the operator most of all.
The chief reason that this machine worked better than mine seems to be that the bottle was coated with varnish between the stopper and coating of lead; this probably did not condense the damp of the air so readily as glass, and consequently the machine worked well when mine refused to work at all.
Monday, 19th March 1770. The machine on being taken out of the box was found to have had the plate and one of the phials broken by some accident. The former was replaced by a spare one. Every part was perfectly dry and worked with great freedom, but a small proportion of electricity only could be excited, at most enough to strike through one card. During all our experiments the floor-cloth conducted as it had done before, though it had not been washed for some weeks. Our experiments were soon cut short by the wind, which was foul, freshening so much that we could not with safety let the machine stand. The day was rather hazy.
Friday, 23rd March 1770. All the day was clear, and the evening also very fine. At sunset the machine was set up. It at first entirely refused to work, but after about a quarter of an hour some sparks were excited. The most, however, that we could do was to obtain a slight shock. The floor-cloth conducted as usual, which we ascertained by resting upon a table or chair, in which case we did not feel the shock as we always did when standing upon the ground.