1883.] 



on Meters for Power and Electricity. 



237 



Fig. 2. 



figure, the distance round it tells nothing ; there is, however, a geo- 

 metrical method by which its size may be found. Draw another line, 

 with a great steepness where the figure is tall, and with a less 

 steepness where the height is less, and with no steepness or horizontal 

 where the figure has no height. If this is done accurately, the height 

 to which the new line reaches will measure the size of the figure 

 first drawn : for the taller the figure is, the steeper the hill will be : 

 the longer the figure, the longer the hill : either cause makes both the 

 size of the figure and the height of the hill greater, and in the same 

 proportion : so the one is a measure of the other : and so, moreover, 

 is the height of the hill, which can be measured by a scale, a measure 

 of the quantity of electricity that has passed. 



The first instrument that I made, which I have called a " cart " 

 integrator, is a machine which, if the lower figure is traced out, will 

 describe the upper. I will trace a circle, the instrument follows the 

 curious bracket-shaped line that I have already made sufficiently 

 black to be seen at a distance, the height of the new 

 line measures the size of the circle, the instrument 

 has squared the circle. This machine is a thing of 

 mainly theoretical interest, my only object in show- 

 ing it is to explain the means by which I have 

 developed a practical and automatic instrument of 

 which I shall speak presently. The guiding principle 

 in the cart integrator is a little three-wheeled cart, 

 whose front wheel is controlled by the machine. This, 

 of course, is invisible at a distance, and therefore I 

 have here a large front wheel alone. On moving this 

 along the table, any twisting of its direction in- 

 stantly causes it to deviate from its straight path ; 

 now suppose I do not let it deviate, but compel it to 

 go straight, then at once a great strain is put upon the table which 

 is urged the other way. If the table can move it will instantly do 

 so. A table on rollers is inconvenient as an instrument, let us there- 

 fore roll it round into a roller, 

 then on moving the wheel along 

 it the roller will turn and the 

 amount by which it turns will 

 correspond to the height of the 

 second figure drawn by the cart 

 integrator. If, therefore, the 

 wheel is inclined by a magnet 

 under the influence of an electric 

 current, or by any other cause, 

 the whole amount of which we 

 wish to know, then the number 

 of turns of the roller will tell us this amount ; or to go back to our 

 water analogy, if we had the weighted board to show current strength, 

 and had not the paddle-wheel to show total quantity, we might use the 



Fig. 3. 



