VOL. LXXXl.] PHILOSOPHICAL TRANSACTIONS. 53 



farther, keeps suspended at its extremity a pith ball electrometer k, so that the 

 electrometer may be about 12 inches distant from the wall. On the outside of 

 the wall there is a wooden box m, to keep that end of the glass tube dry. 



At 2 inches distance of the above-mentioned brass ball l, a bell n is supported 

 by a strong wire, which passing through another hole made in the wall, is made 

 to communicate, by means of a good metallic continuation k, with the moist 

 ground adjoining to the house. A brass ball, -fV of an inch in diameter, is sus- 

 pended between the bell n and ball l, by a silk thread fastened to a nail o. This 

 ball serves for a clapper, by striking between the ball and bell, when the electri- 

 cal charge of the rod is sufficiently strong, p is a small table fixed to the wall 

 under the bell and ball, at a convenient height above the floor, on which Leyden 

 bottles and other apparatus are occasionally placed. Any person versed in the 

 science of electricity, will easily understand that this apparatus is calculated to 

 show the various degrees of atmospherical electricity, and at the same time to 

 avoid the pernicious effects which may be occasioned by thunder-storms, or in 

 short by any great quantity of electricity in the atmosphere. The whole per- 

 pendicular height of both parts taken together, from the moist earth to the up- 

 permost point at the top of the rod, is 5'2 feet. 



Finding however, that notwithstanding all the precaution taken to procure a 

 good insulation, the moist vapour of the atmosphere, fixing on the insulating 

 parts of the apparatus, rendered it imperfect in moist weather; Mr. R. altered 

 the situation of the same rod, so that all the insulating parts are now within the 

 roof of the house. This he effected by a hole through the roof of the house; 

 by which means he now obtains a considerably more constant electricity; which 

 however must not be solely attributed to the superiority of the present mode of 

 insulating, but to the rod's being also elevated to the additional height of 9 feet; 

 so that its pointed part is at present 61 feet above the moist earth. This im- 

 provement of the apparatus, having been made after the conclusion of this 

 journal, will be particularly described in the next, which Mr. R. was continuing. 



It will be necessary just to mention the method he has ])ursued in forming the 

 journal of atmospheric electricity. This has been principally by means of the 

 signs exhibited by the pith balls k, connected with the rod. When he finds 

 these closed, and not attracted by the finger, he then writes no signs of electri- 

 city. When attracted on the approach of the finger, yet not sufficiently charged 

 to repel each other, he writes weak signs of the fluid. When the balls are open, 

 and on the approach of excited glass the balls close, he writes they are electrified 

 positively ; but, if the balls open wider, he writes they are electrified negatively ; 

 and the reverse when he used sealing-wax. When the balls diverge 1 inch and 

 upwards, visible sparks may be drawn at the brass ball l. When sparks are said 

 to have been perceived in any observation, he has generally on that account 

 omitted to note the variable quantities of divergency in the pith balls. Their 



