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."

References
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.

Optical instrument, polarising helioscopic eyepiece, brass / glass, used at Sydney Observatory, made by Hugo Schroeder, Hamburg, Germany, 1874.

A polarising helioscopic eyepiece consisting of a central brass disc with a hole in its surface. Set into the surface of the disc surrounding the hole is a rotatable brass scale. Fixed to the rotating scale is a rectangular metal structure set at an oblique angle. Inside the metal structure there is a rectangular glass lens which is held at an angle by two metal brackets. There is an additional pair of brackets for another lens however no lens is present. There is a hole in the top of the oblique metal structure into which a brass screw fitting has been attached. On the underside of the central brass disc is a metal bracket containing two additional rectangular glass lenses. The lenses are set at an angle and held in place by metal brackets.

Made: Hugo Schroeder; Hamburg, Germany; 1874


Used: Sydney Observatory; Sydney Observatory, Watson Road, Observatory Hill, Sydney, NSW

Owned: Sydney Observatory;

Text engraved in gothic script on the central brass disc reads 'Hugo Schroeder / Hamburg'.

H10380

1874

145 mm

160 mm