Joseph Henry (December 17, 1797[1][2]– May 13, 1878) was an American experimental physicist and inventor who served as the first secretary of the Smithsonian Institution.

[8] His work on the electromagnetic relay was the basis of the practical electrical telegraph, invented separately by Samuel F. B. Morse and Sir Charles Wheatstone.

He intended to go into medicine, but in 1824 he was appointed an assistant engineer for the survey of the State road being constructed between the Hudson River and Lake Erie.

In 1826, he was appointed Professor of Mathematics and Natural Philosophy at The Albany Academy[11] by Principal T. Romeyn Beck.

[13] While in Princeton, he taught a wide range of courses including natural history, chemistry, and architecture, and ran a laboratory on campus.

Decades later, Henry wrote that he made "several thousand original investigations on electricity, magnetism, and electro-magnetism" while on the Princeton faculty.

[14] Henry relied heavily on an African American research assistant, Sam Parker, in his laboratory and experiments.

In an 1841 letter to mathematician Elias Loomis, Henry wrote: The Trustees have however furnished me with an article which I now find indispensable namely with a coloured servant whom I have taught to manage my batteries and who now relieves me from all the dirty work of the laboratory.

In 1848, while Secretary, Henry worked in conjunction with Professor Stephen Alexander to determine the relative temperatures for different parts of the solar disk.

[20] In late 1861 and early 1862, during the American Civil War, Henry oversaw a series of lectures by prominent abolitionists at the Smithsonian Institution.

[21] Speakers included white clergymen, politicians, and activists such as Wendell Phillips, Horace Greeley, Henry Ward Beecher, and Ralph Waldo Emerson.

Orator and former fugitive slave Frederick Douglass was scheduled as the final speaker; Henry, however, refused to allow him to attend, stating: "I would not let the lecture of the coloured man be given in the rooms of the Smithsonian.

[22] Henry was introduced to Prof. Thaddeus Lowe, a balloonist from New Hampshire who had taken interest in the phenomenon of lighter-than-air gases, and exploits into meteorology, in particular, the high winds which we call the Jet stream today.

Henry took a great interest in Lowe's endeavors, promoting him among some of the more prominent scientists and institutions of the day.

With the Southern States seceding from the Union, during that winter and spring of 1861, and the onset of Civil War, Lowe abandoned further attempts at a trans-Atlantic crossing and, with Henry's endorsement, went to Washington, D.C. to offer his services as an aeronaut to the Federal government.

SIMON CAMERON DEAR SIR: In accordance with your request made to me orally on the morning of the 6th of June, I have examined the apparatus and witnessed the balloon experiments of Mr. Lowe, and have come to the following conclusions 1st.

The balloon prepared by Mr. Lowe, inflated with ordinary street gas, will retain its charge for several days.

It can be let up into the air by means of a rope in a calm day to a height sufficient to observe the country for twenty miles around and more, according to the degree of clearness of the atmosphere.

From experiments made here for the first time it is conclusively proved that telegrams can be sent with ease and certainty between the balloon and the quarters of the commanding officer.

Mr. Lowe informs me, and I do not doubt his statement, that he will on any day which is favorable make an excursion of the kind above mentioned.

For these preliminary experiments, as you may recollect, a sum not to exceed $200 or $250 was to be appropriated, and in accordance with this Mr. Lowe has presented me with the in closed statement of items, which I think are reasonable, since nothing is charged for labor and time of the aeronautic.

After the demonstration, Bell mentioned his untested theory on how to transmit human speech electrically by means of a "harp apparatus" which would have several steel reeds tuned to different frequencies to cover the voice spectrum.

The United States Coast Guard honored Henry for his work on lighthouses and fog signal acoustics by naming a cutter after him.

Bronze statues of Henry and Isaac Newton represent science on the balustrade of the galleries of the Main Reading Room in the Thomas Jefferson Building of the Library of Congress on Capitol Hill in Washington, D.C.