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Electricity

Octr 25.1768 five miles South of the Line by guess Long

My Machine

Made by Ramsden. Workd by a flat plate 8 inches diameter the Phial used was 6½ inches in hight and 5½ in diameter without the neck; the distance between the stopper and coating 3 inches; the stopper made of wood and fastned to the glass on the inside by a red cement probably sealing wax. The Electrometer was divided into 30 parts making in all 1½ inches nearest. About nine in the Morn the machine was set up, when we suppos'd ourselves to be somewhat more than five miles south of the line; the day pleasant, but rather cloudy; the ship going between three and four Knotts.

When the plate was first turnd round the Cushions appeard to be damp, adhering to the glass so that it was with dificulty made to move very slowly round, tho the cushions were screwd on as lightly as possible. After wiping them very well the plate was made to go round, and in about ten minutes Electricity was excited, tho but in a small degree. The motion of the ship, and the shaking of the table causd by turning the machine, made the Electrometer (which was a very unsteady one) move backwards and forwards visibly to the eye; so that it was impossible to ascertain exactly at what distance it dischargd the Phial: it however was guessd 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 the shock; which succeeded very ill, the shocks being very small, tho given with the greatest quantity of Electricity that could be got into the Phial. It then, (after having grown by degrees weaker and weaker) ceasd to work intirely; upon which water was applied to the cushions, but without any effect: every thing was then wiped and dried as well as could be done in our situation, the cushions being carried to fire; but no Electric[i]ty perceivable to the touch was communicated to the conductor: whether any was then excited on the surface of the plate we did not then observe. An amalgama of Lead was then applied, which causd a small degree of Electricity, much smaller than at first, which very soon ceasd also, from that time no electric[i]ty perceivable (except by Cantons Electrometer) could be communicated to the conductor, tho the machine was workd near an hour.

In the course of these experiments two thing[s] were observd, differing from the Phaenomena usualy seen. First, the Phial when filld with Electricity as full as the Machine could; would not contain it more than a very few seconds, 3 or 4 by guess; (for no opportunity of measuring by a watch was given, the Machine Leaving off working without any warning when it was not expected.) At the end of this time not the smallest quantity of Electricity was left tho I tried all my Phials 5 in number two of which were such as were describd above: the others were small ones, made much in the same manner, but instead of being coated on the inside filld with leaf gold.

Secondly, the floor of the Cabbin in which the experiments were tried, was coverd with a red floor cloth of painted Canvas, that had been issued to the ship from his majesties stores at Debtford; which was usually washed with salt water every morning, and sufferd to dry without being ever taken up. This provd 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 shockd by another who touchd the conductor w[i]thout having any communication with the first, except by the floor cloth under his feet. This Dr Solander and myself tried several ways, but made more experiments afterwards with Mr Greens Machine as taken notice of in the next paper.

The ill success of these experiments seems to me to have arisen cheifly from the uncommon dampness of the circumambient air which had been observd by everybody since we crossd the tropick and is largely taken notice of in my Journal. By this solution alone all the Phaenomena that appeard may 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; the machine therefore worked faintly for a little while till the damp was condensed on the conductor and cheifly on the surface of the glass Phial and then ceas'd intirely. A small quantity was however always perceivable upon the surface of the plate and even to the end of the conductor.

The Phial tho chargd as full as the machine would fill it even at the time of its best working would not contain the Electrical matter scarce at all owing doubtless to the Communication made by the condensed damp between the Coating and stopper of the Phial; this increasd every moment so that at last it would not contain Electricity at all.

The situation on board a ship would not allow the making use of a fire at least to warm the whole machine as should have been done and would have been a great satisfaction but the motion of the ship, the distance of the galley from the Cabbin and the number of people who are constantly busy there made that impossible.

The dampness of the air compland of here has not been observd now for the first time. Piso in his account of the Brazils p. 5 mentions it and says that victuals &c . which have kept well before spoil immediately here. 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 workd remarkably well in London and full as well as I expected in Madeira.

Octr 25. 1768. 17 Miles south of the line

Mr Greens machine

The machine was made by Watkins; it workd with a flat plate of Glass [ ] inches in diameter; 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 comeing between that and the neck; the Electrometer was divided into 30 parts which containd 1 inch and 1/8.

[1] The plate at first refusd to go round as mine had before done the cushions being drawn together by the Glass which they seemd to adhere to probably from their dampness. After some time turning however this went off and in about 10 minutes Electricity was excited.

The Electrometer was then applied which went off at No 7.

2 Electricity was kept in the Phial 30 seconds without loosing any sensible part

3 a hole was struck through two cards by the discharging wyer.

4 Shocks were given to several people much greater than any that could be Given by my machine.

5 the Phaenomenon of the floor cloth proving a conductor was tried more fully than before. A wyer (b) was passd round the Phial (a) the two ends of which were taken hold of by two people (cc) who each took hold of another person (dd). The operator (e) then touched the Phial with his discharging wyer and receivd the shock through both his arms as did (cc) and (dd) sometimes, tho at others (dd) felt it only in the arms by which they held (cc). The comparative force of the blows which each felt was very dificult to ascertain but we supposd that (cc) felt more than (dd) and probably the operator most of all.

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The chief reason why this machine workd better than mine seems to me 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 near so readily as Glass and consequently the machine workd well when mine refusd to work at all.

Monday March ye 19th 1770 of the Coast of [New Zealand]

Lat. S. Long.

The machine on being taken out of the Box was found to have had by some accident the plate and one of the Phials broken; the former was replacd by a spare one. Every part of it was perfectly dry and workd with great freedom; a small proportion of Electricity only could be excited, the most enough to strike through one card. During all our experiments the floor cloth conductd as it had done before tho it had not been washd for some weeks our experiment[s] were soon cut short by the wind which was foul freshning so much that we could not with safety let the Machine stand. - The day was rather hazey.

Friday March 23d 1770. Lat. Long

All the day was clear and the evening also very fine. At sunset the machine was set up; it at first intirely refusd to work but after about ¼ of an hour some sparks were excited, the greatest however that we could raise it to was only a slight shock. The floor cloth conducted as usual which we ascertaind by resting upon a table or chair in which case we did not feel the shock which standing upon the ground we always did