DR. EVERETT ON ATMOSPHERIC ELECTRICITY. 
349 
reduced commence with. June 1862, and extend to the end of May 1864, thus embracing 
exactly two years. 
The following description of the apparatus is, for the most part, copied verbatim from 
a lecture delivered by the inventor, Sir William Thomson, at the Eoyal Institution, 
May 18th, 1860, as reported in the Proceedings of the Institution*. 
I„ The water-dropping Collector consists of an insulated copper vessel containing 
water, which is allowed to flow out in a fine stream through a brass pipe projecting 
through a hole in a window-frame on the west side of the Observatory into the open air, 
which frame is, for still greater security, composed of ebonite. The nozzle of the pipe 
is 11-J feet above the ground, and 3 feet from the wall of the Observatory. The effect 
of the flow of water is to reduce the copper vessel and its contents to the same electrical 
potential as that point in the air at which the water-stream breaks into drops. 
II. The divided-ring electrometer, of which some of the internal parts are shown in 
fig. 4, Plate XIX. consists of 
(1) A ring of metal (A B) divided into two equal parts (CAD, C B D), of which one 
is insulated, and the other connected with the metal case of the instrument and so with 
earth. 
(2) A very light needle (E) of sheet aluminium, hung by a fine glass fibre (H) and 
counterpoised at G so as to make it project only to one side of the axis of suspension. 
(3) A Leyden phial, consisting of an open glass jar, coated outside and inside in the 
usual manner, with the exception that the tinfoil of the inner coating does not extend to 
the bottom of the jar, which is occupied instead by a small quantity of sulphuric acid. 
(4) A stiff straight wire (F E) rigidly attached to the aluminium needle, as nearly as 
may be in the line of the suspending fibre, bearing a light platinum wire (K) linked to 
its lower end and hanging down so as to dip into the sulphuric acid. 
(5) A case protecting the needle from currents of air, and from irregular electric 
actions, and maintaining an artificially dried atmosphere round the glass pillar or pillars 
supporting the insulated half-ring, and the uncoated portion of the glass of the phial. 
(6) A light stiff metallic electrode projecting from the insulated half-ring through the 
middle of a small aperture in the metal case, to the outside. 
(7) A wide metal tube of somewhat less diameter than the Leyden jar, attached to a 
metal ring borne by its inside coating, and standing up vertically to a few inches above 
the level of the mouth of the jar. 
(8) A stiff wire projecting horizontally from this metal tube above the edge of the 
Leyden jar, and out through a wide hole in the case of the instrument to a convenient 
position for applying electricity to charge the jar with. 
* This lecture, as reported in the Proceedings of the Royal Institution, was sent in the following year, with, 
the photographic curves for four successive days, and an accompanying description, to the Philosophical Maga- 
zine, hut was not inserted ; and down to the present time no full description of the apparatus has been pub- 
lished, the most successful attempt that we have seen being the description of the Electrometers at Kew in the 
*■ Engineer’ for August 9th of the present year. 
