Intelligence and Miscellaneous Articles. 30§ 



the potentials V corresponding to s, D, and for V/D the following 

 numbers : — 



s 



. 2-5 5 10 20 30 40 50 centim. 



D 



. 0-70 1-10 2-37 4-97 7*47 8-33 8-55 „ 



- 3 V 



. 23 28 44 60 69 74 



- 3 V/D . 



. 33 25-5 18-5 12-1 9-2 8-8 



The equivalent striking distances D approach a limit as s increases ; 

 they increase more rapidly than the corresponding potentials. 



In the discharge of electricity from points towards a wire gauze, 

 the velocity of the electrical aura could be determined by means of 

 an anemometer placed behind the wire gauze. 



When the point was at a distance s = 7 centim. between the 

 point and the wire gauze, the following velocities, in metres and 

 seconds, were obtained : — 



D 12 5-7 109 157 207 centim. 



V 1-71 1-69 1-19 0-61 



Hence, by means of the electrical aura, fine particles of dust can 

 be carried to great distances. — Wiener Berichte, xciii. p. 408(1886); 

 Beibl'dtter der PhysiJc, vol. x. p. 641. 



ON A SIMPLE AND CONVENIENT FORM OF WATER-BATTERY. 

 BY HENRY A. ROWLAND. 



For some time I have had in use in my laboratory a most simple, 

 convenient, and cheap form of water- battery, whose design has 

 been in one of my note-books for at least fifteen years. It has 

 proved so useful that I give below a description for the use of other 

 physicists. 



Strips of zinc and copper, each two inches wide, are soldered 

 together along their edges so as to make a combined strip of a little 

 less than four inches wide, allowing for the overlapping. It is 

 then cut by shears into pieces about one fourth of an inch wide, 

 each composed of half zinc and half copper. 



A plate of glass, very thick and a foot or less square, is heated 

 and coated with shellac about an eighth of an inch thick. The 

 strips of copper and zinc are bent into the shape of the letter U, 

 with the branches about one fourth of an inch apart, and are 

 heated and stuck to the shellac in rows, the soldered portion being 

 fixed in the shellac, and the two branches standing up in the air, so 

 that the zinc of one piece comes within one sixteenth of an inch of 

 the copper of the next one. A row of ten inches long will thus 

 contain about thirty elements. The rows can be about one eighth 

 of an inch apart, and therefore in a space ten inches square nearly 

 800 elements can be placed. The plate is then warmed carefullv 

 so as not to crack, and a mixture of beeswax and resin, which melts 

 more easily than shellac, is then poured on the plate to a depth of 

 half an inch to hold the elements in place. A frame of wood 

 is made around the back of the plate with a ring screwed to the 

 centre, so that the whole can be hung up with the zinc and copper 

 elements below. 



When required for use, lower so as to dip the tips of the ele- 



