Nature

First State of the Union Address

Letters to a Friend, Written to Mrs. Ezra S. Carr, 1866–1879

A Short History of the Academy of Natural Sciences of Philadelphia

From North Pole to Equator: Studies of Wild Life and Scenes in Many Lands

On poetic interpretation of nature

Second State of the Union Address

Polar Exploration

Natural History: Mollusca

Natural History of the Ground Squirrels of California

Stars of the Desert

Natural History: Fishes

Devils Tower National Monument

Masters of the Wilderness

Birds of Song and Story

The Stewardship of the Soil

Tales of a Vanishing River

Mushroom and Toadstools

Four-Footed Americans and Their Kin

John Kerry's testimony before the Senate Foreign Relations Committee

Elementary Botany