But the ships went up and down in the spring of 1777.

It would be easy enough to help Burgoyne when the time should come.
It was summer before Howe was ready to move, and by that time he had received instructions that his first aim must be to cooperate with Burgoyne.

First, however, he was resolved to have Philadelphia.
Washington watched Howe in perplexity.

A great fleet and a great army lay at New York.

Why did they not move?
Washington knew perfectly well what he himself would have done in Howe's place.