Grubb, Thomas

(b. 1800; d. Dublin, Ireland, 19 September 1878)

optical engineer.

Grubb was a self-taught Irish mechanic, engaged by the Bank of Ireland to construct and develop machines for printing bank notes. He established a small private observatory near Charlemont Bridge, Dublin, and about 1830, on an adjoining site, he opened a factory for the manufacture of machine tools and reflecting telescopes.

In 1835 Grubb constructed a fifteen-inch equatorial newtonian-cassegrainian reflector for Armagh Observatory, in which, for the first time, a triangular system of balanced levers shared the weight of the primary speculum. He used a similar system in a twenty-inch reflector made for Glasgow Observatory, and with such success that it was adopted, with modifications, by William Parsons, earl of Rosse, for his thirty-six-inch and seventy-two-inch reflectors at Parsonstown.

Grubb’s greatest achievement was his construction, at Charlemont Bridge Works, of a forty-eight-inch equatorial cassegrainian reflector for Melbourne, Australia. This telescope, completed in 1867, was hailed as a triumph of engineering and optical skill. Intended for photography, it had several novel features, among them counterpoises to reduce the pressure of the polar axis-on the bearings. But once on site, the instrument required almost constant adjustment and the mirrors of speculum metal (through no fault of Grubb’s) soon became tarnished. These defects and others temporarily destroyed confidence in this type of telescope and unfortunately delayed its development for some thirty years.

After 1865 Grubb was assisted by his son, Howard, who in 1868 took control of the factory and moved into larger premises in Rathmines, Dublin. A member of the Royal Irish Academy, Grubb became a fellow of the Royal Society in 1864 and a fellow of the Royal Astronomical Society in 1870.

BIBLIOGRAPHY

I. Original Works. A work by Grubb is “On Illuminating the Wires of Telescopes,” in Monthly Notices of the Royal Astronomical Society, 3 (1836), 177–179.

II. Secondary Literature. Short biographies are given in Dictionary of National Biography and Observatory, 2 (1878), 203. Further references appear in “Obituary Notice of Sir Howard Grubb,” in Proceedings of the Royal Society, 135A (1932), iv-ix. Grubb’s activities in telescope making are discussed in H. C. King, The History of the Telescope London, 1955).

H. C. King