The above image is a spectrum of the Sun. It can be seen that it is not “pure” but has some frequencies missing, and therefore represented as black lines.
These black lines are called Fraunhofer Lines and they are named after Joseph von Fraunhofer. Fraunhofer was not an Astronomer. He was “the” premier glass manufacturer in the world and the reason he was one of the first persons in history to view these lines was because his glass was the purest glass that could be manufactured.
No surprise, then, that the Edinburgh Astronomical Institution (EAI) turned to Fraunhofer to make the main (“Objective”) lens of their Transit Instrument for the Observatory for which “only the best” would do. Of interest is that Fraunhofer died aged 39 – due to the poisonous nature of the fumes generated in glass making – just after completing this lens, and although there are other lenses of this great man still in existence, it is believed that this is the last one he ever made. Fraunhofer’s glass making secrets went to the grave with him as he had jealously protected them by never putting them in writing.
After the death of Fraunhofer, construction of the Transit Instrument fell to the Repsold Company in Hamburg. Unfortunately, death again took a turn. Johann Georg Repsold, the owner of the company, was also a Fire Chief in Hamburg and he was killed whilst attending a fire. A degree of uncertainty broke out in the EAI and consideration was made as to whether to cancel this contract and get Troughton and Simms, a famous London based firm who were already building other instruments for the observatory, to build a Transit Instrument.
However, the Repsold Company survived – being taken over by two of Repsold’s sons – and the contract was completed. It is recorded in the Minutes of the EAI on 07/10/1831 that the instrument was in transit to Edinburgh and on 05/11/1831 that it was at last installed and said to be “decidedly the finest Instrument of the kind in Britain”.
The Transit Instrument today
When Thomas Henderson became the first Astronomer Royal for Scotland in August 1834 he immediately employed Alexander Wallace as his Assistant Astronomer. Henderson asked Wallace to manage this instrument and its associated clock while he took charge of the Mural Circle.
Wallace remained in post until his retirement in 1880 and he was virtually the sole user of this instrument throughout its entire productive life.
Dr Bruce Vickery