Notes on the use of alternating current in unloading coal

The receipts of coal in Duluth-Superior Harbor increased from 2,600,000 tons^∗ in 1900 to 8,300,000 tons in 1910. This coal comes principally from Pennsylvania and West Virginia and is brought by rail to Lake Erie ports where it is loaded into boats for transportation to Duluth and Superior. Of the receipts in 1910, two million tons was anthracite and the remainder bituminous coal. At Duluth-Superior Harbor the coal is unloaded from the boats and stored for future demand or loaded directly into cars for shipment to various points in Minnesota, North Dakota, South Dakota and Montana.