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
