Alter, David (1807–1881)

US inventor and physicist. He put forward in 1854 the idea that each element has a characteristic spectrum, and that spectroscopic analysis of a substance can therefore be used to identify the elements present.

Alter was born in Westmoreland County, Pennsylvania, and studied medicine in New York. He spent the rest of his life experimenting and making inventions, working alone and using home-made apparatus. His inventions included a successful electric clock, a model for an electric locomotive (which was not put into production), a new process for purifying bromine, an electric telegraph that spelled out words with a pointer, and a method of extracting oil from coal (which was not put into commercial practice because of the discovery of oil in Pennsylvania).

Alter also investigated the Fraunhofer lines in the solar spectrum. The significance of his work in spectroscopy was not recognized at that time, but his idea was experimentally verified a few years later, and today spectroscopic analysis is extensively used in chemistry and astronomy.