Optical instrument, polarising helioscopic eyepiece, brass / glass, used at Sydney Observatory, made by Hugo Schroeder, Hamburg, Germany, 1874
In 1874, after two years of inquiries, the NSW Government Astronomer H. C. Russell acquired a number of new instruments in preparation for the upcoming Transit of Venus. One of these was a new 11.4 inch telescope (H9886) purchased for the observation of double stars from the optician and instrument maker, Hugo Schroeder.
In 1870 he had made an objective for the Hamburg Observatory and the success of this instrument may have been one reason Russell sought him out. As well as the telescope Russell purchased some additional instruments from Schroeder for use with the telescope. These were this solar polarising eyepiece designed for viewing the sun, a filar micrometer mounted on a graduated circuit (H10007), and some eyepieces (H10294). A sun diagonal (H10295) used in conjunction with the Schroeder telescope was purchased separately.
This solar polarising eyepiece enabled the observer to look at the sun without coloured glasses, so that the actual colouring of the suns surface could be seen.
In the following excerpt from the 1874-1875 Astronomer's Report Henry Russell describes its operation, "In this eye-piece advantage is taken of the polarization of light reflected from a glass surface, and two pairs of reflectors are used and so arranged that one pair might be made polarize at right angles to the other, in which position it stops nearly all of the sunlight; by altering this angle the sunlight may be made of any convenient intensity, and the alteration is made by simply turning a handle."
Russell, H., C., "Report of Astronomer for 1874 & 1875', New South Wales Government Printer, 1876
Geoff Barker, August, 2007
The eyepiece was made in 1874 by Hugo Schroeder in Hamburg Germany.
The eyepiece was used at the Sydney Observatory, Watson Road, Observatory Hill, Sydney, New South Wales, Australia.