The Endeavour Journal of Joseph Banks 1768–1771 [Volume Two]
Octr 25.1768 five miles South of the Line by guess Long…
Octr 25.1768 five miles South of the Line by guess Long….
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)1 could be communicated to the conductor, tho the machine was workd near an hour.page 277
In the course of these experiments two thing[s] were observd, differing from the Phænomena 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 Phænomena 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 page 278 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.
1 John Canton (1718-72), one of the most distinguished electrical experimenters of the time; F.R.S. 1749; he invented among other things the electrometer and the electroscope.