Sunda strait leads from the Indian Ocean to Java Sea;
and, after that, there were some more straits leading to the China Sea.

Late in the afternoon the wind got lighter; and as there was a strong
current setting towards the southwest, through the straits, they
couldn't sail as fast as the current carried them. So the _Industry_ was
carried back to Anger; but she started again very early in the morning,
when there was more wind and when the tide was different.

When little Jacob and little Sol came on deck they saw three ships,
going the other way. They wondered what they were, and they asked the
mate. And the mate smiled and said that two of the ships were Dutch and
he supposed that they were going to Batavia. And he thought that the
other ship was American and he hoped that it would take the letters they
had left at Anger. Little Jacob hoped that it would; but little Sol
didn't seem to care. And, all of that day, they watched for more ships,
and they saw land, now and then, far off on the horizon. It was very
hot, for they were almost at the equator; so that even little Sol was
contented to keep still. And, towards night, they saw one of the
sailors getting the lead line ready.

The lead is just a big lump of lead, like a sinker that is used on a
fishing line, and it is tied to the end of a long line that has the
fathoms marked on it in much the same way that the log line has the
knots marked; but the marks on the lead line are really six feet apart.
And the lead itself has the lower end just a little bit hollowed. The
sailor who was getting it ready first made sure that the line was all
clear, without any knots or kinks in it. And, when he had seen that the
line was all right, he took up the lead and smeared some grease on the
bottom of it. The sailor was the old man who had given little Jacob the
model of the brig.

Little Jacob was surprised. "What is that?" he asked. "Is it grease?"

The sailor was amused. "It's grease," he said, "sure enough."

"And what is it for?" asked little Jacob again. "I hope you don't mind
telling me."

"No, lad," said the sailor. "Be sure I'll tell you. It's to bring up
some of the bottom so's the cap'n can tell where we are."

Little Jacob didn't understand. "I don't see," he said, "how Captain
Solomon can tell where we are, that way."

The sailor laughed. "Well, no," he said. "I s'pose you don't. Well, it's
this way. The bottom of the sea is different in different places. In