TEANSACTIONS OF SECTION G. 815 



in order to avoid the injurious effects of water, the ropes are encased in wood boxes 

 strung down the side of the shaft and roughly insulated on hrackets. Underground, 

 one of the ropes is simply wrapped with old brattice cloth or tarpaulin. On the 

 surface the ropes are laid in brick channels filled in with gas tar and coal dust, but 

 it appears from the last trials that it is sufficient to lay the ropes side by side in the 

 same material ; there is no appreciable loss of current. The fact that old ropes are 

 only worth a few pounds per ton enables a profuse use of cables to be made, and at 

 one of the installations the current is conveyed a distance of nearly 1,300 yards 

 (double distance) with a resistance of only -05 ohm, nearly one-half of which is 

 due to the insertion of a length of — high conductive copper cable. 



A brief description of the last installation — which includes lighting of all surface 

 works (extending over five acres), the underground workings in vicinity of the shaft, 

 and, at a distance of 620 to 700 yards away, the church, schools, and houses — was 

 given. 



The author remarked upon the practicability of economical extension of installa- 

 tions by utilising old material such as ropes, old rails, water and gas mains, and 

 gives the resistance of the latter as tried in one case, and concluded with a few 

 general remarks. 



8. Dynamos for Electro-Metallurgy. By Professor George Forbes, M.A. 



The author wished to draw the attention of manufacturers and others to the 

 enormous importance and the large field for new applications of the art of electro- 

 metallurgy. The cost per pound of copper of finished articles, such as kitchen 

 utensils, &c., neglecting cost of material, when these are electro-deposited instead 

 of being manufactured as at present, is generally only 15 per cent., often 5 per 

 €ent., of the present cost of manufacture. When we possess machines capable of 

 producing large currents of electricity at low pressure, an enormous industry will 

 be immediately opened, and nearly all manufactures will be benefited by the new 

 economical process. A few branches need alone be mentioned to show what may 

 be hoped for, such as the production of sugar pans, copper fire-boxes, copper tubes, 

 and even the coppering of ships' bottoms. These startling applications involve no 

 new principle. The processes are as old and sure as could be desired. It is only 

 the magnitude of the operation which is startling. The only cause of delay at 

 present is the want of a suitable machine for supplying a large current. 



It is now three years since the author realised that most dynamos as at present 

 supplied have complications introduced with the one object of getting a hio-h 

 electric pressure. This is not required in electro-metallurgy, and for this purpose 

 we can revert to the simplest modes of generating electric current. The author 

 believes that the machine he has constructed is the most perfect, electrically and 

 mechanically, of any that could be devised. The first large-sized machine con- 

 sisted of a disc of iron capable of revolving on a spindle. Round its circumference 

 are rubbing contact springs attached to a ring-casing which contains a coil of in- 

 sulated copper wire. This casing, with the contained coils, is concentric with the 

 disc. The whole is now encased in an iron mass, to which are attached the bear- 

 ings. Contact makers or brushes are also attached to the ends of the spindle. 

 These form, say, the positive terminal. The ring-casing thus forms the negative 

 terminal. Independent excitement is given to the insulating coil of wire. 



The advantages of such a machine are (1) its simplicity; (2) no wasted power 

 in reversing the magnetism of the revolving part ; (3) no reversal of current, as in 

 the armature coils of ordinary dynamos ; (4) its enormous current ; (5) no Foucault 

 currents. 



The author made a machine, like the above, but double, with discs llj inches 

 diameter. Its output was 18,000 watts, the energy required to magnetise it was 

 200 watts. Such a result has never been obtained with any other dynamo. Two 

 difficulties were encountered. Firstly, the end-thrust was apt to be very great if 

 the disc were not properly central. This was overcome by giving up the disc form 

 and using a solid cylinder of iron, going right through the machine, for the arma- 

 ture. This had the further advantage of diminishing the internal resistance. The 



