In the years following 1897 large sums have been spent for betterments and enlargements. Some $68,500,000 have been invested from the proceeds of the sale of prior lien bonds and of miscellaneous assets, and over $18,000,000 have been temporarily withdrawn from income for the same purpose.[640] Grades have been reduced, lines straightened, new branches built, real estate acquired, track relaid and ballasted, bridges strengthened and renewed, equipment rebuilt and increased in amount, and other similar betterments undertaken. It is a work which all the great American systems have carried on, but the Northern Pacific has surpassed even the Union Pacific in the extent of its operations. Ordinary maintenance requirements have not meanwhile been neglected, and in 1906 and 1907 the Northern Pacific set aside $2,000,000 for depreciation of equipment, which is over and above the other sums which have been mentioned. The company owned 1255 locomotives on June 30, 1907, of an average weight of 174,000 pounds; in 1898 it had owned 542 of an average weight of 104,000 pounds. It had 42,000 freight cars in 1907 with an average capacity of over 33 tons; it had possessed 18,500 in 1898 of an average capacity of 22 tons. Seventy-five per cent of the main line was laid with track of 72 pounds or over in 1906, but only thirteen per cent in 1898. In consequence heavier trains are run,[641] at a less expense per ton, and the net revenue is correspondingly increased. Even the liberal expenditures which have hitherto been made are insufficient, however, for present conditions, and the stockholders have approved a proposal to issue $93,000,000 of new common stock at par for the purpose of extending the Northern Pacific’s mileage and facilities.[642] The endeavor to stimulate traffic to fill the trains has led to important developments. In order to increase the exchange of commodities between their territory and the Middle West, to establish stable conditions on transcontinental business and thereby to secure back loading for their cars, the Great Northern and Northern Pacific in 1901 arranged for the purchase of the Burlington system which connected both their lines with Chicago. The refusal to share their purchase with Mr. Harriman led to the competitive purchase of Northern Pacific stock by rival interests, and to the retirement of the Northern Pacific preferred, but did not prevent the consummation of the deal.[643] This purchase has been a profitable one. The Burlington has paid in dividends upon its stock almost enough to cover the interest on the bonds issued to acquire it, and the indirect effects of its control have satisfied expectations. Indeed, the east-bound lumber traffic has so developed that the Great Northern has recently raised its lumber rates in order once more to equalize east- and west-bound shipments.