SECT. 13. In estimating what shall constitute the said twenty-five per cent. of the gross earnings of said several leased railroads, out of which their rentals are to be paid, there shall be first deducted from twenty-five per cent. of their respective gross earnings, six per cent. per annum on all amounts expended by said board of trustees for the permanent improvement of said railroads respectively. SECT. 14. Said Vermont and Massachusetts, Fitchburg, and Troy and Boston Railroad Companies are severally authorized to lease their franchises and property to said board of trustees. SECT. 15. Said board of trustees is further authorized, with the approval of the governor and council, to lease or purchase necessary terminal facilities, and also to lease any railroad now built, or that hereafter may be built, lying in the tunnel route between Boston and Lake Ontario. SECT. 16. In the carriage of through passengers and merchandise, the rates of transportation shall be estimated pro rata per mile, and the Hoosac Tunnel shall be estimated at such length in miles, not exceeding fifty, as shall seem equitable to the trustees. SECT. 17. In the management of such railroads as shall come under the operation of said board of trustees, there shall be no unequal discriminations in freights, fares or facilities in favor of or against different persons, places or connecting railroads. SECT. 18. In case of the lease of the Fitchburg Railroad under the terms of this act, the said board of trustees is authorized and directed to purchase terminal facilities in Boston, westerly of the freight station of the Boston and Maine Railroad and to arrange with the Eastern Railroad Company for an interchange of stations in Boston in such manner as to obviate the necessity of passenger trains on the Eastern Railroad, Boston and Maine Railroad and Fitchburg Railroad crossing the tracks of the other, and the Eastern Railroad Company is hereby authorized, with the assent of said trustees, to take or purchase all the land, depot property and buildings of the Fitchburg Railroad Company, situated in Boston south of the channel or passage-way for vessels through the Fitchburg Railroad bridge over Charles River, said property to include all the draws and drawbridges over the passage-way for vessels.