July 14, 1787 (Click the link to read Madison’s notes)
The delegates decided not to limit representation of new western states and defeated an effort to make Senate membership based on on population.
Influences on the Delegates
Madison appealed to the Dutch government as an example of one means of representation:
In the Dutch Confederacy the votes of the provinces were equal; but Holland, which supplies about half the money, governed the whole Republic. He enumerated the objections against an equality of votes in the second branch, notwithstanding the proportional representation in the first. 1. The minority could negative the will of the majority of the people. 2. They could extort measures, by making them a condition of their assent to other necessary measures. 3. They could obtrude measures on the majority, by virtue of the peculiar powers which would be vested in the Senate. 4. The evil, instead of being cured by time, would increase with every new State that should be admitted, as they must all be admitted on the principle of equality. 5. The perpetuity it would give to the preponderance of the Northern against the Southern scale was a serious consideration. It seemed now to be pretty well understood, that the real difference of interest lay, not between the large and small, but between the Northern and Southern, States. The institution of slavery, and its consequences, formed the line of discrimination. There were five States on the Southern, eight on the Northern side of this line. Should a proportional representation take place, it was true, the Northern would still outnumber the other; but not in the same degree, at this time; and every day would tend towards an equilibrium.
By the end of his speech, Madison came back to the elephant in the room – the debate between the Northern and Southern states, principally over slavery.
Although no one took up his theme in this session, the delegates voted down a proportional system in the Senate.
For a nice summary of the Convention debate over slavery see this article.
1787 Constitutional Convention Series
Constitutional Convention Series (click the link)