Page:Incandescent electric lighting- A practical description of the Edison system.djvu/95

 ever varying with the change in the temperature about them. As an offset to this seeming defect in the apparatus small spools of copper wire, accurately measured, are placed in the circuits of fine wire leading to the bottles. The conditions which increase the resistance of the bottles, decrease the resistance of the spools; and thus one offsets the other to maintain a constant resistance.

These meters are in use both in this country and abroad in large numbers, and give satisfaction wherever used. They are simple and inexpensive in construction as well as economical and accurate in operation; qualities which have directly influenced their adoption in all the large central stations throughout the country.