464 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



the R. s., to read the annual dissertation on some philosophical subject, insti- 

 tuted by our worthy member the late Mr. Baker, I have endeavoured to pursue 

 some electrical experiments, to explain how far the Electrophorus perpetuus may 

 be accounted for on the almost generally received theory of Dr. Franklin, of 

 positive and negative electricity. 



This electrical instrument consists of 2 different pieces; viz. 1. a metallic 

 body, in the form of a plate, or any other convenient figure, furnished with an 

 insulating handle, to be used for lifting it up ; and 2. a flat non-conducting sub- 

 stance, such as glass, resin, or some other non-conducting matter, on which 

 the metal plate is placed. This machine, invented by Mr. Volta, a learned gen- 

 tleman of Como, is certainly a valuable acquisition to the electrical apparatus. 

 Once excited, it is for a long while ready to afford electricity enough for all ex- 

 periments which do not require a very great force ; and it has the advantage of 

 not being so much affected by damp weather, as the common machines with 

 glass globes, cylinders, disks, &c. It is very easily put in action by a slight 

 friction with a dry hand, a piece of leather, a rough skin of a hare, a cat, or 

 some other animal. It is as easy to excite, with this machine, a negative as a 

 positive electricity. It has the advantage of being capable at almost all times of 

 affording at pleasure such a force of electricity as is wanted, even to such a de- 

 gree, that the metal plate is no longer able to contain all the electric fluid com- 

 municated to it ; but throws it every way, either on the metal on which the 

 resinous cake is usually flxed, or into the air : and this increase of electrical 

 power is obtained by the easiest means ; for instance, by charging with the elec- 

 trophore a coated phial, and placing it afterwards on the resinous cake itself, or 

 on the metal plate placed on the resinous cake (provided the metal plate be less 

 in circumference than the resinous cake, and no metallic communication exist 

 between the metal plate and that metal on which the cake is fastened.) If the 

 knob of the phial, thus placed, be touched by the finger, and then taken away, 

 holding it by the knob, the force of the electrophore is found to be remarkably 

 increased. 



But a more pleasing way of increasing the electrical force of this instrument 

 is by transferring alternately the metal plate from one resinous cake to another, 

 and touching it after it is placed on the cakes. By this method both cakes ac- 

 quire continually more and more electricity ; so that in a short time, by this al- 

 ternate translation, the metal plate returns from either cake quite ovej-charged ; 

 and thus Leyden phials may be charged by it very strongly, and even so as to 

 break them. It is \ery remarkable, that by this method the metal plate returns 

 from one cake in a ])ositive, and from the other in a negative state. This 

 manner of increasing the two electricities was found out by my learned friend 

 Dr. Klinkoch, jjrofessor in the university of Prague, soon after I had given him 



