362 On ike Electric Column. 



to he that em])IoYerl by Signior Zamboni, wlio ha'i made ?<ome 

 interesting discoveries on the general structure of the instrument. 

 He employs a vertical iieedle supported by a delicate pivot cr 

 knife-edge a little above its centre of gravity, the position of 

 which may be readily altered by means of a sliding weight at- 

 tached to the lower extremity of the needle, which may by that 

 means be so adjusted as to possess the properties of an accurate 

 scale-beam, and will maintain its oscillations over a considerable 

 space by a very slight impulse. 



The upper end of the needle, for at least an inch, is formed 

 of varnished glass; and on this a ring of gold, or a gilded ball of 

 pith 'or cork, is fixed ; the axis of the needle is supported midwar 

 between two vertical cohinins insulated, but connected together 

 at bottom, so that the upper ends of the columns become the 

 po'<itive and negative extremities of the series ; the upper and 

 insulated extremity of the needle comes in contact alternately 

 with each of these ends, receives its electrical state, and recedes 

 towards the other, where the same process ensues ; and thus the 

 vibrations of the needle are maintained with great constancy over 

 a considerable space. 



Fig. 3 represents the form I have employed for this con- 

 struction : the needle is supported by a brass arm which slides 

 on one of the columns; it is suspended by a delicate pivot, and 

 has at its summit a fine varnished glass tube to which a gilded 

 ball is aiiixed ; tlie lower cxtreniitv of the needle is provided with 

 a sliding weiglit, by whicli the relation of the centre of gravity to 

 the point of suspension is accurately adjusted : to render tlie 

 contacts perfect, and least liable to change, the gilded ball does 

 not strike tlie brass caps,of the columns, but touches alternately 

 two gold wires connected witli them. 



In this construction the nee31e is not moved bv the direct at- 

 traction of the column ; but being once ])r.t into a state of vibra- 

 tion, its motion, which would naturally decline, and finally ter- 

 i:;inate by the operation of friction and by the resi'^taiicc of the 

 air, n renewed at each contact by the impulse of electrical at- 

 traction, which is altcrnatelv exerted on the needle in opposite 

 directions by each extremity of the column ; and as this attrac- 

 tion does not sensibly act on the pendulum until it is very near 

 the attracting surface, its operation commences when it is mo<t 

 wanted, and, without materially affecting the action of the pen- 

 dulum in any other way, occasions it to describe constantly 

 equal arcs at everv vibration. 



It is obvious, that by connecting a proper lever and ratchet- 

 wheel with the ax's of the needle, motion may be readily com- 

 municated to indexes, or to other wheels ; and this I am in- 

 formed has been done during the past year, by some experimcn- 



talibts 



