NUOVE NOTIZIE STORICHE SULLA VITA E SULLE OPERE DI MACEDONIO MELLONI 



39 



brought near 1, 2, 3, 4 it immediately exerts its induction action upon the plates a, in ad- 

 dition to the action of A. Ali these and a thousand others are the simplest possible vesults 

 of the theory. 



You speak of screening the * pendules accouple „ frotn the action of A whilst you 

 examine thein by an exited electric (rad?). But in that case the pendules give no indication 

 of the state of the part to which they are attached. They do not receive their final state by 

 conduction from the part they are fixed to, but only by induction as a part of the conducting 

 mass B C: if they are expand to the inductive force of A they will acquire the opposite 

 state; if they are perfectly screened they will be neutral, or if they are so near orso expand 

 to sorrounding conductors as to be in a position to curry on the forces, they will assume 

 the c state, which is the same as the stato of A. 



I have often shewn my audience this condition of the pendoloas balls, by placing the 

 cylinder and its balls well insulated, in different positions as respects the industrie ball A : 



m or 



Fig. 7. 



Fig. 8. 



I c 



Fig. 9. 



thus (fig. 10), when in this position, B and its balls will be in the reverse state to A, and e 

 and its ball in the same state as A : but then (fig. 11) held it by an insulating handle thus and 

 through B stili acquires a state contrary to A, yet the balls attached to it by conducting matters 

 shew the other state, or that of A and c. 



Again, if the ball A and cylinder B C (fig. 12) retain their position, it is very easy to 

 have the balls hanging to B, in the state of B, or by approaching an uninsulated ball or 

 screen, either at 1 or 2 or 3, to make them assume the contrary state on that of C, or by 

 adjustment of distance to be perfectly indifferent. 



Trusting to the truth of the principle I have described I am accustomed to use wire 

 gauze instead of a continuous metal piate, for screens and other apparatus, which I waut my 

 audience to see through : and I have plates like those described above constructed of such wire 



Fig. 10. Fig. 11. Fig. 12. 



gauze. Through the openings are three or four times the diameter of the wire, yet no electri- 

 city of induction can pass through them, and a piate of such wire gauze is as impervious to 

 condnetion as a piate of metal. 



I make a cylinder of such wire gauze part of the conductor of the machine, but the most 

 delicate tests inside gave no indication of Electricity there. On the lecture table, I threw a net 

 of common twine over my gold leaf electrometers connecting it well with the ground, and they 

 are rendered perfectly safe from charge of the machine, which by induction would destroy them at 

 once if not so guarded. 



Ali of which, illustrates the powerful effect of screens in static inductive action. I have 

 published no account of these things because they are simple consequences of my theory: b .t 

 De La Rive who happened to see them once in the lecture room here, gave a brief account of 

 them in the Geneva Journal. 



And now. my dear friend, I will relieve you from a tiresome lecture. You speak of the 



