Friday, 1 May 2009

Tuesday May 1, 1894

Christie's altazimuth, c.1914 - image from Science and Society Picture Library, original on loan from Royal Observatory, Greenwich.
Went to Troughton & Simms in the afternoon about new Altazimuth (in progress), glass diaphragm with scales at right angles for measure of star photo’s, mounting of spectroscope on Great Equatorial &c. Mr Simms showed me an alloy of platinum (2 parts) & copper (1 part) recommended by Johnson & Matthey as uncorrodible, which he proposed to use for the circle of the new Altazimuth.

William Christie, Astronomer Royal

RH says..... Christie here refers to the Great Equatorial, which is the name normally associated with the 12.8-inch Merz, installed when George Airy was Astronomer Royal. The 28-inch had replaced this in the ROG's Great Equatorial Building, and Christie evidently transferred the name. Johnson and Matthey, a company that still exists, was a precious metals assayer that had produced the standard weights and measures for the International Metric Commission.

The 28-inch telescope had a half-prism spectroscope, designed by Christie himself, that had to be mounted underneath the telescope - a much larger instrument than the one that the building and mount had originally supported. According to the obituary of Christie by Turner, this half-prism design was pioneering, but the "soundness of its principles has since been questioned".

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