September, and, as I have said, the British pushed on to
Philadelphia and entered it in triumph on the 26th."

"Papa, what are _chevaux de frise_?" asked Grace.

"They are ranges of strong frames with iron-pointed wooden spikes," he
answered; then went on:

"In addition to these, the Americans had erected batteries on the
shores, among which was the strong redoubt called Fort Mercer, which,
and also Port Mifflin on the Mud Islands, I have already mentioned.
Besides all these, there were several floating batteries and armed
galleys stationed in the river.

"All this troubled the British general, because he foresaw that their
presence there would make it very difficult, if not impossible, to keep
his army supplied with provisions; also they would be in more danger
from the American forces if unsupported by their fleet.

"Earl Howe, as you will remember, was at this time in Chesapeake Bay
with a number of British vessels of war. As we have just been doing, he
sailed down the one bay and up into the other, but was prevented, by
these fortifications of the Americans, from continuing on up the
Delaware River to Philadelphia.

"Among his vessels was one called the _Roebuck_, commanded by a Captain
Hammond. That officer offered to take upon himself the task of opening a
passage for their vessels through the _chevaux de frise_, if Howe would
send a sufficient force to reduce the fortifications at Billingsport.

"Howe was pleased with the proposition and two regiments of troops were
sent from Chester to accomplish the work. They were successful, made a
furious and unexpected assault upon the unfinished works, and the
Americans spiked their cannon, set fire to the barracks, and fled; the
English demolished the works on the river front, and Hammond, with some
difficulty, made a passage way seven feet wide in the _chevaux de
frise_, so that six of the British vessels passed through and anchored
near Hog Island."

"Did they immediately attack Forts Mifflin and Mercer, papa?" asked
Lulu.

"It took some little time to make the needed preparations," replied the
captain. "It was on the 21st of October that Count Donop, with twelve
hundred picked Hessians, crossed the Delaware at Cooper's Ferry, and
marched to the attack of Fort Mercer. The Americans added eight miles to
the extent of their march by taking up the bridge over a creek which
they must cross, so compelling them to go four miles up the stream to
find a ford.

"It