182 STELLAR PHOTOGEAPHY. 



Earl of Rosse and the Washington refractor. An important part of the work of 

 Dr. Gould at the Cordoba Observatory consisted in securing photographs of the 

 principal clusters in the southern hemisphere, but the results have not yet been 

 published. 



During the past three or four years, stellar photography has been pursued at 

 various observatories. Dr. Gill has undertaken to make a map of the southern 

 heavens by photography. A catalogue of five hundred stars, whose light was deter- 

 mined from their photographs, was published by the Rev. T. E. Espin in the Pro- 

 ceedings of the Liverpool Astronomical Society, Transactions, No. 3, 1884. The 

 most elaborate investigation is that of the MM. Henry, of the Paris Observatory. 

 Admirable photographic maps of the stars have been constructed with the inten- 

 tion of substituting them for the charts of Peters and Chacornac. It is impossible, 

 however, to make a statement of the photographic work in progress at the present 

 time, on account of the rapid advances now being made in this department of 

 astronomy. 



In 1863, Dr. Huggins obtained a photographic image of the spectrum of Sirius, 

 but it was so ill-defined that it presented no indications of lines. (Phil. Trans., 1864, 

 p. 428.) The first successful photograph of the spectrum of a star was obtained by 

 Dr. Henry Draper, in 1872. A spectrum of Vega was taken, in which four lines 

 were visible. (Amer. Jour. Sci., 1879, XYIII.) The work was afterwards resumed 

 by each of these astronomers, but was confined to the brightest stars. (Proc. Amer. 

 Acad., XIX. 231; Phil. Trans., 1880, p. 669.) The method employed was the same 

 in both cases, and consisted in concentrating the light of the star by means of a 

 large telescope upon the slit of a spectroscope placed in its focus. A narrow slit 

 was necessary to secure good definition, and very perfect adjustment of the tele- 

 scope was required to keep the image of the star upon the slit. 



Preliminary Experiments. 



A great variety of preliminary experiments were made in connection with 

 this research, by the aid of an appropriation from the Rumford Fund. In 1882, 

 a photograpliic lens having an aperture of 7 inches and a focal length of 37 

 inches was procured, and attached to the equatorial mounting in the west dome of 

 the Harvard College Observatory. Afterwards the camera containing this lens was 

 mounted in the meridian and directed towards the equator. The plate-holder was 

 attached to a car, which was drawn by clockwork at the rate of 0.16 in. per minute 

 from west to east. If the plate was at rest, each star in turn, as it approached the 



