332 THE POPULAR SCIENCE MONTHLY. 



the Leyden philosophers correctly stated the conditions necessary to 

 the success of the experiment. Hence the phial received the name of 

 the Leyden-phial, or Leyden-jar. 



The discovery of Rleist and Cungeus excited the most profound 

 interest, and the subject was explored in all directions. Wilson, in 

 1746, filled a phial partially with water, and plunged it into water, 

 so as to bring the water surfaces, within and without, to the same 

 level. On charging such a phial the strength of the shock was found 

 greater than had been observed before. 



Two years subsequently Dr. Watson and Dr. Bevis noticed how 

 the charge grew stronger as the area of the conductor in contact with 

 the outer surface increased. They substituted shot for water inside 

 the jar, and obtained substantially the same effect. Dr. Bevis then 

 coated a plate of glass on both sides with silver-foil, within about an 

 inch of the edge, and obtained from it discharges as strong as those 

 obtained from a phial containing half a pint of water. Finally, Dr. 

 Watson coated his phial inside and out with silver-foil. By these 

 steps the Leyden-jar reached the form which it possesses to-day. 



It is easy to repeat the experiment of Dr. Bevis. Procure a glass 

 plate nine inches square; cover it on both sides with tin-foil six inches 

 square. Connect one side with the earth and the other with the 

 machine. Charge and discharge : you obtain a brilliant spark. 



In our experiment with the golden fish (Fig. 22), we employed a 

 common form of the Leyden-jar, only with the difference that to get 

 to a sufficient distance from the glass, so as to avoid the attraction of 

 the fish by the jar itself, the knob was placed higher than usual. But, 

 with a good flint-glass tumbler, a piece of tin-foil, and a bit of wire, 

 you can make a- jar for yourself. Bad glass, remember, is not rare. 

 In Fig. 24 you have such a jar. T is the outer, T' the inner coating, 

 reaching to within an inch of the edge of the tumbler G. W is the 

 bit of wire fastened below by wax, and surmounted by a knob, which 

 may be of metal, or of wax or wood, coated with tin-foil. In charging 

 the jar you connect the outer coating with the earth say with a gas- 

 pipe or a water-pipe and present the knob to the conductor of your 

 machine. A few turns will charge the jar. It is discharged by lay- 

 ing one knob of a " discharger " against the outer coating, and causing 

 the other knob to approach the knob of the jar. Before contact, the 

 electricity flies from knob to knob in the form of a spark. 



A " discharger " suited to our means and purposes is shown in Fig. 

 25. II is a stick of sealing-wax : W W a stout wire bent as in the 

 figure, and ending in the knobs B B'. These may be of wax coated 

 with tin-foil. Any other light conducting knobs would of course 

 answer. The insulating handle H protects you effectually from the 

 shock. 



Sec. 18. Explanation of the Leyden -Jar. The principles of 

 electrical induction with which you are now so familiar will enable 



