Glenn Beck

He could sink into dark moods that Jefferson called depressions of the mind.

But when it came to endurance, precision, and loyalty, Jefferson trusted him without hesitation.

As his co-leader, Lewis turned to his former commander and close friend from his army days, William Clark.

Clark was 33, four years older than Lewis and different in temperament.

He was steadier, more laid back.

He was from Kentucky, raised on rivers and forests, and he was an exceptional map maker and boatman.

In the spring of 1803, Lewis went to Philadelphia to study with the leading scientist of the day.

He trained like an astronaut preparing to go to the moon.

He studied astronomy, botany, anatomy, math, and medicine.

On this mission, he would have to be a scientist, a doctor, cartographer, journalist, and military leader.

He assembled a giant inventory of supplies and gifts for the Native Americans that they would encounter, including silver peace medals stamped with Jefferson's profile.

These were not just trinkets.

For Indians, gift exchange was a vital sign of friendship.

President Jefferson's written instructions were explicit.

This was an ambitious scientific and diplomatic mission.

The Corps of Volunteers for Northwest Discovery was comprised of 45 men, including a man named York, who was William Clark's slave.

On May 14, 1804, the expedition finally pushed off and began forcing its way up the Missouri River.

The river did not exactly cooperate.

The current was strong, the banks choked with mud and willows, the heat was oppressive, the mosquitoes, the gnats, swarmed in clouds.

The men rowed, they pulled, they sailed when the wind allowed, and often hauled the heavy keelboat upstream by rope wading in waist-deep water.