314 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



■ : > TABLE II. 



The proportionable mnnher of inhabitants that die annualbj in the folhming places. 



Whites in Jamaica 1 in 5 Amsterdam 1 in S-i Country Parishes. 



Vienna I . . 193 Breslaw 1 . . 25 Pais de vaud 1 in 45 



London 1 . . '20| Berlin 1 . . 26^ Country parishes in Brandenburgh 1 . . 45 



Edinburgh 1. . C0-| Northampton ... 1 . . '2b\ Others in Brandenburgh 1 . . 5u 



Leeds 1. . "^l-l Shrewsbury I . . 26| A country parish in Hantsforpi' yrs. 1 . . 50 



Dublin 1. . 22 Liverpool 1. . 274 Island of Madeira 1. . 50 



Rome 1. . 23 Manchester I. . 2S Stoke Damerel in Devon, for 1 yr. 1 , . 54 



IX. Some Electrical Experiments. By Mr. fVilliam Swift, of Greenwich, p. 155. 



Mr. Swift contrived an electrical apparatus, to show the different effects of 

 points and balls at the upper termination of conductors, to secure houses and 

 magazines of powder from damage by lightning. He represented the clouds by 

 interposing 3 feet of water insulated, instead of continuing the metal from the 

 prime-conductor ; which he apprehended to be analogous to the natural clouds. 

 The clouds, being charged, slide on a frame with a graduated edge ; and, as 

 they pass the length of the frame, they make 5 revolutions round their own 

 axis ; for they are represented by a semi-circle, the radius of which is 18 inches, 

 consequently its extent is nearly 4-i- feet, and formed with materials well covered 

 with metal. He placed 3 houses at a certain distance from the frame, and 

 equally distant from each other. Each house has a conductor, and is connected 

 with magazines of powder, called a, b, c ; the reason for making the clouds a semi- 

 circle is, that when turned back they may be charged from the machine, with- 

 out affecting, or being affected by, the points or balls on the tops of the houses 

 A, B, and c ; and, by means of their motion round their own axes, he could 

 increase or diminish at pleasure the velocity. He fixed an electrometer on one 

 of the conductors of the machine, and put points for the upper terminations of 

 the conductors of the houses. Having thus prepared the machine, the semi- 

 circular cloud being turned back, that is, within ; the machine is charged till 

 the index of the electrometer rises upwards of QO" ; the cloud being then put in 

 motion, as it slides along the frame, revolves over the house a, with its length 

 of 44- feet : in its passage it empties itself, the electrometer falling to O, but not 

 the least explosion is perceived. The cloud then turning back in its progressive 

 motion in the frame, is charged again while it passes on to b ; at which point, 

 by means of its motion round its axis, it revolves over the conductor b ; it 

 empties itself, the electrometer falls, and no explosion is perceived : the same 

 thing happens in the passage over the house c. 



The machine remaining in the position as before, he placed balls of ~ of an 

 inch diameter, at the upper terminations of the conductors of the houses a, 

 B, c, and with these balls, the experiments proceed almost as before; that is, 

 the matter passes off with a little hissing noise, and now and then it gives a 

 slight explosion, the smallness of these balls diflering little from points. But 



