Solar spectroscope by Howard Grubb, Dublin, 1871

Three-prism solar spectroscope with automatic prism adjustment for minimum deviation and a fixed equatorial mounting with drive by Howard Grubb, Dublin, dated 1871. Supplied by the Royal Society of London to J.B.N.Hennessey who used the instrument at Vincent Hill, Dehra Dun in the Indian foothills [7,000 ft.] of the Himalayas to map the solar spectrum between 1871-5.

Dated 1871, this three-prism spectroscope with equatorial stand was made in Dublin by Howard Grubb. Better known as a maker of telescopes, Grubb supplied this instrument to the Royal Society of London for an expedition to India. Here between 1871-5, it was used by J B N Hennessey to map and measure in detail the spectrum of the Sun. The instrument was located on Vincent Hill, Dehra Dun at over 7000 feet (2300m) in the Indian foothills of the Himalayas. It was hoped that the high altitude would provide clearer air and show greater resolution than had been seen at sea level. In the event, the results were disappointing with little if any extra detail being recorded.