This collection contains mostly entomological material, with much information on the description and identification of particular insects, entomological collections, and the study of entomology in Europe and the United States. In addition, there are materials on medicine and hospitals during the American Civil War, on the Corps of Topographical Engineers, the United States Army, on natural history in the United States, and on the LeConte's family. Some letters are written to President Rutherford B. Hayes and concern the Commissionership of Agriculture, for which LeConte was considered, but not appointed. Letters of John Eatton LeConte and Joseph LeConte are included.

Benjamin Silliman (1779-1864, APS 1805) was a scientist and educator. As a professor of chemistry at Yale University from 1802 to 1853, and pioneering teacher of chemistry, mineralogy and geology, Silliman was largely responsible for the conversion of Yale College to Yale University, with strong medical and scientific departments.

Founded in 1743 by Benjamin Franklin, the American Philosophical Society was the first learned society in the United States. For over 250 years, the Society has played an important role in American cultural and intellectual life. Until the mid-nineteenth century, the Society fulfilled the role of a national academy of science, national library and museum, and even patent office. Early members of the Society included Thomas Jefferson, David Rittenhouse, Benjamin Rush, Stephen Peter Du Ponceau, George Washington, and many other figures prominent in American history. The Archives of the American Philosophical Society consists of 192.25 linear feet of material, organized into thirteen record groups dating back to 1743. The Society's archives extensively documents not only the organization's historical development but also its role in American history and the history of science and technology.

This is a collection of letters, letterbooks, account books, scrapbooks, etc., concerning the families of Robert Hare and Thomas Willing. The letters and other documents include early family material, as well as documents written by numerous family relations, and some obviously only collected by them. The Willing family letters (1744-1901) are diverse, concerning family matters, business, society, comments on the Civil War, etc. There are numerous letters from Thomas Willing, many concerning his banking career, as President of the Bank of North America and later at the first Bank of the U.S. The Hare family letters (1724-1965) are more extensive and diverse, including much on travel in the U.S. and elsewhere. There is a letter from Robert Hare Jr. concerning steam engines, and letters from Horace Binney Hare concerning his education at Harvard, 1860, his trip to San Francisco and the west, 1862, and numerous letters written while a soldier in the Civil War. There are many letters from Horace Binney (1780-1875, DAB) to his daughter Esther, who was married to John Innes Clark Hare (1816-1905, DAB), concerning family travel and court cases. There are also letters from outside the family, such as those from Dorothea L. Dix. The bound volumes include, among others: Robert Hare letterbooks (1824-1825, 1841-1857), estate records, and laboratory expense accounts (1818-1860); G. H. Hare's journal or log of cruises aboard the U.S. United States (1841) and U.S. Flint (1845); Horace Binney Hare's 1862 journal of his trip to San Francisco. There are account books and accounts (1754-1795) kept by Thomas Willing; accounts of the controversy over the estate of John Innes Clark; and records of the First Colored Wesley Methodist Church of Philadelphia (receipt book, 1820-1848; minute book, 1827-1844). There are also Philadelphia court records, and minutes of the Common Council of the city, 1832.

This rich collection of letters and documents, which was assembled by Sol Feinstone (1888-1980) over a period of fifty years, includes material on almost all notable Americans from before the Revolution to the 1850's, as well as prominent Europeans, and there are documents relating to military affairs. There are substantial groups of letters from: John Adams, Henry Dearborn, Alexander Hamilton, Jedediah Huntington, Thomas Jefferson, Lafayette, George Washington, and a long run of letters from a Massachusetts military surgeon named Samuel Adams. Many letters, though written by Revolutionary figures, relate to events that occurred before or after the War.