For the purpose of making reports to the department of revenue, the gross earnings of railway companies, owning or operating a line or lines of railway partly within this state and partly within another state, or other states, or territory, or territories, upon their line or lines within this state, shall be ascertained and reported by said railway companies as follows, to wit: The aggregate of the earnings upon business originating and terminating within this state, upon business originating in this state and terminating elsewhere, upon business originating elsewhere and terminating in this state, and upon business neither originating nor terminating in this state but carried on or done over the line or lines in this state or over some part thereof, shall be reported; and with respect to all such interstate business the earnings in this state for the purpose of report shall be actually computed upon the basis of the length of haul or carriage in this state as compared with the length of haul or carriage elsewhere. It is hereby declared that for the purpose of making reports looking to the assessment of railway property for taxation, the gross earnings or business done or carried partly within this state and partly in another state, or other states, or territories, shall be that proportion of the entire earnings of such business that the haul or carriage in this state bears to the entire haul or carriage.