Maclean star-spectroscope (1891/2)

The Report of the Astronomer Royal for 1892 records that a Maclean star-spectroscope had been procured ,and that a Rowland diffraction grating with 14,438 lines to the inch, has been ordered from Brashear for use with the new 28-inch refractor (which was about to be installed in place of the 12.8-inch Merz).

There is no indication that the spectroscope was ever used and this is the only mention of it in the volumes of Greenwich Observations or the Reports of the Astronomer Royal.



Although Christie gives the name as Maclean, it is more likely to have been McClean

Frank Maclean invented his star-spectroscope in about 1875. The following brief description is taken from the biographical notice at the beginning of A descriptive catalogue of the McClean collection of manuscripts in the Fitzwilliam museum. Montague Rhodes James, Cambridge (1912)

‘This form of spectroscope is a direct-vision instrument; it is furnished with a slit, which, however, may be dispensed with in stellar observations; in place of the usual plano-convex lens a cylindrical lens is inserted between the slit and the prism, and thus a lengthened image of the slit is formed in its principal focal plane. The observer thus sees a broad spectrum in which the lines can be much more readily detected than in the linear spectrum of a star. Mr McClean has not given any published account of this instrument, but he had it constructed by Browning; and by reason of its compactness and efficiency, and the ease with which it could be manipulated, it was and still is widely used.’

Instructions for its use were published by John Browning on pages 26–29 of his How to work with the spectroscope : a manual of practical manipulation with spectroscopes of all kinds.