Page:Incandescent electric lighting- A practical description of the Edison system.djvu/106

. For this amount there has been obtained here a plant, which is considered equal, if not superior, to any of this class, and at a cost of twenty to thirty per cent, less than is expended for similar ones.

I will take up the next consideration of the operating expenses of such a plant. In order to place the company (m an earning basis we have to secure to start with a certain number of lights or an equivalent in lights and power to clear the necessary general and operating expenses, which will exist regardless of the smallness of the load; in other words, we must have for such a capacity-plant not less than 5,000 lights with an average income of $8 per light per year to clear the general incidental and operating expenses. This figure we may consider as our unit of operating capacity. From this we can figure the increased earnings and profits for the larger number of lights connected. There exists practically a constant ratio of variable and fixed operating expenses. By variable expenses we mean those