RESISTANCE BY A METHOD BASED ON THAT OF LORENZ. 
41 
The shaft runs in bearings made of a special alloy of tin (69 per cent.), zinc (29‘6 
per cent.), and copper (l'4 per cent.), this being the best non-magnetic alloy we know 
of in which a copper aluminium shaft will run without trouble. The pedestals PP and 
bed B, supporting the bearings, are of phosphor bronze, except for slabs of stabilit 
T, 6 mm. in thickness, which insulate the bearings from the bed. The upper part of 
a pedestal is bolted to the lower part by phosphor-bronze bolts L, stabilit washers 
W, and stabilit tubes being used to insulate the upper and lower parts. The insulation 
resistance between the shaft and the bed has been measured on many occasions, but 
has never been less than a thousand megohms. If two metallic discs with uninsulated 
rims and conductors are employed, such insulation is essential, but it is not necessary 
with insulated conductors and segments such as we have used. 
The oil feed (F) and return pipes (B) are of copper and are insulated from the 
pedestal by glass and ebonite tubes and oil-resisting rubber washers. Oil throwers 
are fitted to the shaft and effectually prevent the oil travelling outwards from the 
bearings. 
Section 6.—The Rotating Conductors which Pass from the Edge of One 
Disc to the Edge of the Other Disc. 
We have already briefly described the system of ten conducting wires passing from 
disc to disc, and it will be realised that the discs in the present apparatus serve only 
to support the radial conductors and are employed for no other purpose. The wires 
used consist of No. 26 double silk-covered copper wire, shellacked, and covered with 
silk tube. 
In order to place the ten wires in position, the shaft was drilled centrally and 
parallel to its length from the coupling between frhe two discs to points within 20 cm. 
of the discs, and radial holes were drilled in the shaft in these latter positions. On 
the coupling between the discs blocks of ebonite are screwed, and these support 
terminals to which the ends of the wires can be attached. Ten wires pass from the 
segments attached to the edge of one disc, through a channel milled in the side of the 
disc, and again through a brass tube screwed on the shaft, into a radial hole; after 
passing through the central hole drilled in the shaft they emerge at the coupling, and 
the free ends of the wires are attached to terminals on the ebonite blocks. Similarly, 
ten wires pass from the edge of the other disc to corresponding terminals, and by 
making suitable connections between the terminals we obtain a system of ten 
conductors which pass between the segments on the two discs. As already explained, 
the path of the conductors is unimportant, conditionally that they pass through the 
coils. 
On the edge of a disc ten segments of stabilit are screwed. Some of these can be 
seen in the photograph (fig. 3), and in the sketch (fig. 5) ; a sectional view of a 
segment attached to a disc is shown in fig. 5 c . On emerging from the channel milled 
VOL. CCXIV.—A. G 
