American physician, chemist, and pioneer geologist and mineralogist.

Jackson received his M.D. from Harvard Medical School in 1829. He continued his medical studies at the University of Paris, also attending lectures on geology at the Royal School of Mines. He returned to Boston in 1832 and started a private medical practice but abandoned medicine in 1836 to establish a laboratory for the teaching of analytic chemistry. One of his students was a young dental surgeon, William Thomas Green Morton (Morton, William Thomas Green), with whom Jackson worked on chemical methods for painless dentistry.

In 1845 Morton learned from Horace Wells that ether could be applied externally as a local anesthetic, and he began to undertake his own experiments with ether. In September 1846 Morton sought Jackson's advice about ether inhalation for surgical anesthesia. Later, following Morton's successful demonstration of ether anesthesia at Massachusetts General Hospital on Oct. 16, 1846, Jackson claimed credit for the triumph and denounced Morton as a swindler and a forger; years of controversy and lawsuits resulted.

Jackson's contentiousness and propensity for controversy are illustrated in other incidents. Having met Samuel Morse in 1832, Jackson later declared that he himself had told Morse the basic principles of the telegraph, and he initiated litigation that continued for years. Jackson worked as a geologist in New England and was assigned by the U.S. Geological Survey to report on the Lake Superior region. His enduring scientific reputation rests mainly on his accomplishments as a geologist.

In 1873 Jackson was admitted to an asylum for the mentally ill, where he spent the remainder of his life.