ELECTRICAL APPARATUS. 



303 



city is communicated to its interior coating, it is necessary 

 that the same quantity should be removed from the exterior, 

 which would otherwise counteract the negative electricity 

 by which the charge is sustained. To effect this, a com- 

 munication is established with the earth, or with the interior 

 coating of a second jar, the outside coating of which again 

 may communicate with the interior of a third, and thus a 

 series of insulated jars may be charged from each other, as 

 shown in the figure, taking care to withdraw the opposing 

 electricity from the last. Price, each, $2.25. 



Leyden Jar with Discharging Fi - 359 - 



Electrometer. Fig. 359 repre- , 

 sents the arrangement for pro- 

 ducing a series of discharges 

 from a Leyden jar, for any par- 

 ticular purpose, without the in- 

 terference of the operator, and 

 also the mode of use ; a, repre- 

 sents the prime conductor of an 

 electrical machine ; 6, a Leyden 

 jar ; on the wire communicating 

 with the interior is fixed an arm 

 of glass, c, on the end of which 

 is cemented the brass knob D, 

 through this knob a wire, f d, 

 slides, so that the ball d may be brought to any required 

 distance from the knob of the jar, e. A careful inspection 

 of the figure will show how this discharging electrometer 

 acts, and how, by increasing or lessening the distance be- 

 tween d and e, the strength of the charge may be regulated. 



Price, $2.50 and $3.00. 



Eudiometer. (Fig. 360.) This instrument is Fi s- 360. 

 used for exploding gases, which being inflamed 

 by the electric spark has given rise to various 

 instruments called eudiometers, one of the most 

 simple of which is shown in the margin. It 

 consists of a thick glass tube closed at the upper 

 end, and open below, where it dips into a cup or 

 basin of mercury. It is graduated along the 

 side, and has two wires through the upper part 

 which approach each other. The tube may be 



