and constantly used there a portion of
its property, the Court commended the State for taking "as a basis of
assessment such proportion of the capital stock of the company as the
number of miles over which it ran cars within the State bore to the
whole number of miles, in that and other States, * * *" This, said the
Court, was "a just and equitable method of assessment;" one which, "if
it were adopted by all the States through which these cars ran, the
company would be assessed upon the whole value of its capital stock, and
no more."[660]

THE UNIT RULE

And pursuing the same course of thought, the Court, in Adams Express
Company _v._ Ohio,[661] decided in 1897, sustained that State in taxing
property worth less than $70,000.00 at a valuation of more than half a
million, on the ground that the latter figure did not exceed, in
relation to the total capital value of the company, the proportion borne
by the railway mileage which the company covered in Ohio to the total
mileage which it covered in all States. To the objection that "the
intangible values" reached by the tax were derived from interstate
commerce, the Court replied with the "cardinal rule * * * that whatever
property is worth for purposes of income and sale it is also worth for
purposes of taxation,"[662] which obviously does not meet the issue.
What the case indubitably establishes is that a State may tax property
within its limits "as part of a going concern" and hence "at its value
as it is in its organic relations," although those relations constitute
interstate commerce.[663] In short, values created by interstate
commerce _are_ taxed.

Thus emerged the concept of an "apportioned" tax, or as it is called
when applied to the problem of property valuation, the "unit rule,"
which till 1938 afforded the Court its chief reliance in the field of
Constitutional Law now under review. The theory underlying the concept
appears to be that it is always possible for a State to devise a formula
whereby it may assign to the property employed in interstate commerce
within its limits, or to the proceeds from such commerce, a value which
it may tax or by which it may "measure" a tax, without
unconstitutionally burdening or interfering with interstate commerce,
while at the same time exacting from it a fair return for the protection
which the State gives it. The question in each case is, of course,
whether the State has guessed right.

APPORTIONED PROPERTY TAXES