236 



Mr. C, Vernon Boys 



[March 2, 



the other during a time. The term meter should be confined to 

 instruments of the second cLass only. 



As with water so with electricity, there are two kinds of measuring 

 instruments, one, of which the galvanometer may be taken as a type, 

 which shows by the position of a magnet how strong a current of 

 electricity is at a time, and the other, which shows how much 

 electricity has passed during any time. Of the first, which are well 

 understood, I shall say nothing ; the second, the new electric meters 

 and the corresponding meters for power, are what I have to speak of 

 to-night. 



It is hardly necessary for me to mention the object of making 

 electric meters. Every one who has had to pay his gas bill once a 

 quarter probably quite appreciates what the electric meters are going 

 to do, and why they are at the present time attracting so much 

 attention. So soon as you have electricity laid on in your houses, as 

 gas and water is laid on now, so soon will a meter of some sort be 

 necessary in order that the companies which supply the electricity 

 may be able to make out their quarterly bills, and refer complaining 

 customers to the faithful indications of their extravagance in the 

 mysterious cupboard in which the meter is placed. 



The urgent necessity for a good meter has called such a host of 

 inventors into the field, that a complete account of their labours is 

 more than any one could hope to give in an hour. Since I am one of 

 this host, I hardly like to pick out those inventions which I consider 

 of value. I cannot describe all, I cannot act as a judge and say these 

 only are worthy of your attention, and I do not think I should be 

 acting fairly if I were to describe my own instruments only and 

 ignore those of every one else. The only way I see out of the difficulty 

 is to speak more particularly about my own work in this direction, 

 and to speak generally on the work of others. 



I must now ask you to give your attention for a few minutes to a 

 little abstract geometry. We may represent any changing quantity, 



as for instance the strength of an 

 electrical current, by a crooked 

 line. For this purpose we must 

 draw a straight line to represent 

 time, and make the distance of 

 each point of the crooked line 

 above the straight line a measure 

 of the strength of the current at 

 the corresponding time. The size 

 of the figure will then measure 

 the quantity of electricity that 

 has passed, for the stronger the current is, the taller the figure 

 will be, and the longer it lasts the longer the figure will be, either 

 cause makes both the quantity of electricity and the size of the 

 figure greater and in the same proportion : so the one is a measure of 

 the other. Now it is not an easy thing to measure the size of a 



Fig. L 



