402 THE ADDRESSES, LECTURES, ETC., OF 



[At this point the lecturer was interrupted by a violent report, 

 resulting in the breakage of some glass in the dome of the theatre, 

 which, fortunately, fell outwards, only slight fragments descending 

 into the body of the hall. Windows towards the back of the 

 building were broken, but the Secretary having at once taken 

 steps, and ascertained that the explosion had occurred outside, the 

 lecturer immediately resumed ; and it was only after the lecture 

 that it was known that the real cause of the report heard was the 

 explosion of dynamite below the offices of the Local Government 

 Board.] 



The effect of variation of the resistance of a dynamo-machine 

 is given in Fig. 2, Plate 9. The dash and dot line represents the 

 electro-motive force in volts, the complete thin line the horse- 

 power which the machine absorbs, and the dotted line the power 

 developed in the outer circuit, the complete thick line gives the 

 current in the outer circuit in Amperes. You will observe that 

 in proportion as the resistance of the machines increases, both the 

 power expended and power developed diminish, the loss being the 

 difference between these lines. The effect is the height up to the 

 dotted lines, and it at once becomes evident that the best result 

 is obtained with not quite 1 Ohm resistance. Fig. 3, Plate 9, shows 

 how a dynamo in series differs from a dynamo in shunt. In an ordi- 

 nary dynamo, the effect increases rapidly with increase of 'velocity. 

 If the machine were set to work, say with incandescent lights, it 

 will be seen that it would at a low speed give very poor results ; 

 but when a certain speed had been obtained, it would be more 

 constant ; by the shunt winding, you find, on the contrary, a 

 diminution of effect with increase of speed ; whereas in a third 

 (the composite, before described) mode of winding, we can obtain 

 the greatest constancy of effect. 



I shall now show you some of the effects that can be produced 

 in transmitting power. In a yard adjoining this Institution a 

 portable steam engine has been erected giving motion to a D 2 

 dynamo-machine, capable of developing about 8 HP. of electrical 

 energy, or 746 x 8 = 5968 Watts. This power is conveyed through 

 an insulated wire to the coils of a D 7 dynamo-machine, the 

 rotating axis of which is practically in one piece with that of a 

 centrifugal pump, by means of which water can be raised in con- 

 siderable quantities, and when forced through a nozzle may be 



