64 
MESSRS. W. DE LA RUE AHD H. W. MULLER OR THE 
right hand spring to the wire A g ; the negative current from Z to the upright 
on the other side of the revolving disc, only partly seen, thence through the upper 
spring to Z'. 
Besides this we have a contact breaker very similar in appearance, and shown 
in situ in fig. 9 on the top of the dwarf cabinet of battery No. 1, containing 1080 
powder-cells ; this cabinet top is of ebonite and forms our 
Eig. 10. ordinary working bench. The contact breaker, B B, is placed 
in a position preceding the discharging key in order from the 
poles of the battery ; we have several revolving discs belonging 
to this piece of apparatus which make and break from 352 to 
2112 times in a second. M M' represents a revolving mirror, 
which has a multiplying wheel, and in which the reflection of 
the discharge in a vacuum tube can be seen. S S' is a short 
contact key used when a condenser is employed, and it is 
wished to charge it up without causing the current to pass 
through any resistance. In the circuit we have a set of coil- 
resistances from 1 to 1,000,000 ohms ; these are specially insu- 
lated, the wires running in grooves on insulating cylinders made 
of paraffined cardboard, in order that they may be kept at a 
distance ; besides this set of resistances we have fluid resistance 
tubes like that represented in fig. 10 ; all but one have adjust- 
able wires in order to vary the resistance ; two are charged 
with equal parts of water and glycerine, two with distilled 
water ; each has a plug P to throw the resistance out of circuit. 
ohms. 
No. 1 has a total approximate resistance of 30,500,000 
„ „ 4,000,000 
„ „ 2,690,000 
„ „ 6,150,000 
Total fluid resistances 43,340,000 
V' 
These resistances gradually diminish by the absorption of 
ammoniacal salts from the atmosphere, and this necessitates 
occasionally the entire renewal of the fluid. 
We have two tangent galvanometers of different degrees of sensitiveness specially 
insulated, which, can be put in circuit by the withdrawal of two plugs, and also an 
induction coil, the primary of which may be brought into circuit ; it is No. 819 
of Apps’s make, the particulars of which are as follow : — 
