headwaters of Back
River, passing Cushman Point through the Cowseagan Narrows, and into the
more open waters below. Three or four miles farther would take them to
Montsweag Bay, of which mention has been made, that body of water being
twice or thrice as wide as the river.

Suddenly Chester asked an odd question:

"Do you think the launch was injured by that spurt this forenoon?"

"She ought not to have been, for she has gone through the strain more
than once and for a longer time. Why do you ask?"

"Somehow or other, it seems to me she isn't running exactly right."

"What is wrong?"

"I can't put my finger on it; I may say I _feel_ it--that's all."

"Well, you are right, for I have had the same misgiving ever since we
left Wiscasset. I have tried to figure it out, but can't and am waiting
for it to develop, hoping all the time it won't--hello! there it comes!"

While the speed of the boat was not affected, the engine began hissing
with vicious persistency.

"Take the wheel, Chester, while I look around."

He first examined the spark plugs, knowing that if one was broken the
result would be what had just taken place, but all were intact. He had
turned the switch, stopping the motor, and next inspected the valve caps
where a fracture or loosening would have caused the hissing. They were
sound and tight and the gaskets where the exhaust and intake pipes
connected with the cylinders were tight.

"I've found it!" he called to Chester. "It's an open compression cup,
which is easily fixed; I am glad it is nothing worse."

Remembering the lessons he had been taught, the young Captain soon
corrected the fault and resumed progress. The launch, however, was held
down to a comparatively slow pace, for the slight slip naturally caused
misgiving. Several minutes passed with all going well.

"It seems to me safe to give her more speed," said Chester. "At this rate
we sha'n't reach home until late at night."

"All right; turn on more power--no, don't! _Ouch!_"

Alvin snapped his fingers, as one does when they are burned. He had
placed them upon the exhaust pipe, which was growing red hot.

"Shut her off! The mischief is to pay."

Knowing from the gesture of the Captain what was the matter, Chester
asked, as he obeyed the request:

"What causes that?"

"There is either something wrong with the water pump, the spark is
retarded, or a lack of sufficient lubrication, causing the motor to heat.
It will take some time