494 REPORT — 1867. 



down the air-insulation by disruptive discharge. The electric action is 

 explained simply thus : — The carriers, when connected by the connecting 

 springs, receive opposite charges by induction, of which they deposit large 

 proportions the next time they touch receiving springs. Thus, for example, 

 if the jar be charged positively, the carrier emerging from the inductor 

 connected with the inner coating carries a negative charge round to the 

 receiving spring connected with the outside coating, while the other carrier, 

 emerging from the inductor connected with the outside coating, carries 

 a positive charge round to the receiving spring connected with the inside 

 coating. If the carriers are not suiRcieutlj^ well under cover of the inductors 

 during both the receiving contacts and the connectiiig contacts to render the 

 charges which they acquire by induction during the connecting contacts 

 greater than that which they carry away with them from the receiving con- 

 tacts, the rotation, even in the proper dii'ection for replenishing, does not 

 increase, biit, on the contrarj', diminishes the charge of the jar. The de- 

 viations of the inductors from the circular cylinder referred to above have 

 been adopted to give greater security against this failure. A steel pivot 

 fixed to the top of the vulcanite shaft, and passing through the main cover, 

 carries a small milled head {y, fig. 1) above, on the outside, which is spun 

 rapidly round in either direction by pressing the finger on it, and thus in 

 less than a minute a small charge in the jar may be doubled. The dimi- 

 nution of the charge, when the instrument is left to itself for twenty-four 

 hours, is sometimes imperceptible ; but when any loss is discovered to have 

 taken place, even if to the extent of lU per cent., a few moments use of the 

 replenisher suiRces to restore it, and to adjust it with minute accuracy to the 

 required degree by aid of the guage to bo described presently. The ininciple 

 of the " replenisher " is identical with that of the " donbler " of Bennet. In 

 the essentials of its construction it is the same as Yarley's improved form of 

 Nicholson's " revolving doubler." 



§ 13. The gauge consists of an electrometer of Class III. The moveable 

 attracted dislc is a square portion of a piece of very thin sheet aluminium of 

 the shape showii at x in fig. 4. It is supported on a stretched platinum wire 

 passing through two holes in the sheet, and over a very small projecting 

 ridge of bent sheet aluminium placed in the manner shown in the magnified 

 di'awing, fig. 3. The cuds of this wire are passed through holes in curved 

 springs, shown in fig. 4, and are bent round them so as to give a secure 

 attachment without solder, and without touching the straight stretched part 

 of the wii'e. The ends of the platinum wire (p, /3) are attached by cement to 

 the springs, merely to prevent them from becoming loose, care being taken 

 that the cement does not prevent metallic contact between some part of the 

 aluminium wire and one or both of the brass springs. I have constantly 

 found fine platinum wire rendered brittle by ordinary solder apphed to 

 it. The use of these springs is to keep the platinum wire stretched with 

 an approximately constant tension, from year to year and at various tempera- 

 tures. Their fixed ends are attached to round pins, which are held with their 

 axes in a line Avith the fibre by friction, in bearings forming parts of two ad- 

 justable brass pieces (y, y) indicated in fig. 4 ; these pieces are adjusted once 

 for all to stretch the wire with sufficient force, and to keep the square attracted 

 disk in its proper position. The round pins bearing the stretching springs are 

 turned through very small angles by pressing on the projecting springs with 

 the finger. They are set so as to give a proper amount of torsion tending to 

 tilt the attracted disk (a) upwards, and the long end of the aluminium lever (o), 

 of which it forms a part, downwards. The downward motion of the long end 



