412 THE ADDRESSES, LECTURES, ETC., OF 



hundred and forty-six such "Watts are equal to 1 HP. ; therefore, 

 if a machine was given to you of say 10,000 Watt power, you 

 would know at once that it would take about 13 HP. to drive it, 

 to which you would have to add 1 per cent, for f rictional losses. 

 If we wished to know the effect from that machine, say in work- 

 ing incandescent lights, we may calculate that 3 Watts produce 

 one candle of effect, whereas in the case of a powerful arc light 

 1 Watt is capable of producing 3-candle power. 



I should have alluded to a number of instruments which have 

 been lent me by the kindness of Professors Ayrton and Perry, 

 They are machines for measuring the different electric quantities, 

 the Volt, the Ampere, and the dynamic effect. I have here, also, 

 an instrument kindly sent me by the Edison Company, which 

 measures the electric quantity in Coulombs. It is based upon the 

 principle of work done chemically. A given current produces an 

 amount of chemical work, and by the amount of chemical work so 

 produced in a branch circuit, the current that has flowed through 

 is estimated. I have already alluded to the dynamometer I 

 usually employ which measures the current in Amperes. This 

 dynamometer consists of one fixed coil surrounded by another coil 

 of a single turn at right angles to the former, through both of 

 which the current passes, so that there will be an attraction 

 between the one wire and the coil of wires, which is proportionate 

 to the square of the current passing ; and by the aid of a Table 

 which I have here, I. can interpret the deflection produced on the 

 index in Amperes. But we have lately improved upon this in a 

 veiy simple manner, so as to get the reading at once in Ampere- 

 Volts or Watts. The only difference between the two instruments 

 is, that in the latter case the stationary coil consists of many con- 

 volutions, and is of very high resistance, and the single convolution 

 of thick wire, suspended freely, is of very low resistance (see Fig. 4 , 

 Plate 8). Now, when a current flows through a high resistance, 

 we measure its potential, and when through a low resistance, its 

 quantity, hence the mutual attraction between the two is no 

 longer according to the square of the current, but as the energy 

 of the current, and we get Volt- Amperes of current, or Watts. 



In conclusion I would only observe that I should have wished 

 to have drawn attention to the various kinds of dynamo-machines 

 which have been developed by different inventors ; but it would 



