whole,
its implied negative operation on State power has been uneven, at times
highly variable. * * * Into what is thus left open for inference to
fill, divergent ideas of meaning may be read much more readily than into
what has been made explicit by affirmation. That possibility is
broadened immeasurably when not logic alone, but large choices of
policy, affected in this instance by evolving experience of federalism,
control in giving content to the implied negation."[652]

DEVELOPMENT OF THE APPORTIONMENT RULE

At the outset the Court appears to have thought that it could solve all
difficulties by the simple device of falling back on Marshall's opinion
in Brown _v._ Maryland;[653] and on the same day that it set aside
Pennsylvania's freight tax by appeal to that transcendent precedent, it
sustained, by reference to the same authority, a Pennsylvania tax on the
gross receipts of all railroads chartered by it, the theory being that
such receipts had, by tax time, become "part of the mass of property of
the State."[654] This precedent stood fourteen years, being at last
superseded by a ruling in which substantially the same tax was held void
as to a Pennsylvania chartered steamship company.[655] A year later the
Court sustained Massachusetts in levying a tax on Western Union, a New
York corporation, on account of property owned and used by it in the
State, taking as the basis of the assessment such proportion of the
value of its capital stock as the length of its lines within the State
bore to their entire length throughout the country.[656] The tax was
characterized by the Court as an attempt by Massachusetts "to ascertain
the just amount which any corporation engaged in business within its
limits shall pay as a contribution to the support of its government upon
the amount and value of the capital so employed by it therein."[657] And
drawing on certain decisions in which it had sought to limit the
principle of tax exemption as applied in the case of railroads chartered
by the United States, it expressed concern that "the necessary powers of
the States" should not be destroyed or "their efficient exercise" be
prevented.[658] Three years later Pennsylvania, still in quest of
revenue, was sustained in applying the Massachusetts idea to Pullman's
Palace Car Company, a "foreign" corporation.[659] Pointing to the fact
that the company had at all times substantially the same number of cars
within the State and continuously