December 11, 1908] 



SCIENCE 



851 



and they are in rapid orbital motion. During the 

 investigation for parallax, it was found that the 

 proper motion of the larger star, as determined 

 from comparison with other stars, was slowly 

 changing its direction, having in the past six or 

 seven years changed about 8° or 9°, from 239° 

 to 247°. This is undoubtedly due to the orbital 

 motion of the two stars. It shows that the small 

 star must have a rather large relative mass. The 

 masses of these two stars can be accurately de- 

 termined by measuring the position of A, with 

 reference to near-by stars. 



The Ccelostat Telescope of the Dominion Observa- 

 tory: J. S. Plaskett. 



This paper contains a description illustrated 

 by lantern slides of a new installation for solar 

 research at Ottawa. A ccelostat and secondary 

 mirror, each of 20 inches aperture, feed a concave 

 of 18 inches aperture and 80 feet focus. Owing 

 to local conditions the beam from the concave 

 has to pass under the secondary mirror to a focus 

 in the basement of the observatory. Notwith- 

 standing the diflferent and less advantageous con- 

 ditions the solar definition is in general very good, 

 much better than obtained with the refractor 

 more suitably situated. The ccelostat is covered 

 by a house, moving back on rails and the beam 

 passes through a shed and short tunnel to the 

 focus. Both house and shed are thoroughly 

 louvered. A grating spectroscope of the Littrow 

 form, with Brashear 6-inch objective of 23 feet 

 focus, and Michelson plane grating ruled surface, 

 4J X 4i inches, arranged to rotate around its 

 optical axis, will be used with this telescope for 

 spectroscopic investigation of the solar rotation, 

 sun spots, etc. 



Camera Objectives for Spectrographs: J. S. 

 Plaskett. 



This paper contains an accoimt of tests for 

 definition and flatness of field performed on a 

 number of different types of lenses used in and 

 especially made for speetrographic work. The ad- 

 vantages of some new forms by Brashear and 

 Zeiss over those previously used is illustrated 

 diagrammatieally. For work with a single prism 

 a new objective by Brashear with widely sepa- 

 rated elements, both of the same material, light 

 crown, gives the best field, while for three-prism 

 work another single material by Zeiss, in this 

 case of the prism material, performs most satis- 

 factorily. Neither of these forms can be used 

 with larger angular aperture than f/10. For 

 shorter focus lenses the Zeiss Tessar seems to be 

 most suitable. A description of the effect upon 



the definition and flatness of field of changing the 

 separation of the elements will be given. 

 The Distribution of Eruptive Prominences on the 

 Solar Disk: Phiue Fox. 



This communication reviews a paper presented 

 to the American Association for the Advancement 

 of Science at the Chicago meeting on " The De- 

 tection of Eruptive Prominences on the Solar 

 Disk " and summarizes the observations on their 

 distribution as follows: 



Spot birth is always accompanied by and gen- 

 erally preceded by eruptions. While the spot 

 continues active the prominences will be present, 

 generally following it at the edge of the penumbra. 

 Spots beginning to decline are also accompanied 

 with eruptions which will be seen at the ends of 

 the bridges. In the case of complex spots where 

 we have a large leader spot and another at the 

 tail of the stream the eruptions follow the pre- 

 ceding spot and precede the following spot and 

 are seen among the smaller spots of the stream. 

 Eruptions are rarely seen preceding the leader 

 spot and as seldom found following the trailer. 



The eruptions about the spot groups are prob- 

 ably due in part to the interference of the whirls 

 about the spots. Judging from the direction of 

 motion indicated by the whirls of calcium and of 

 hydrogen shown on the spectroheliograms, and 

 from motion in some of the prominences, I find 

 the direction of the whirls in the northern hemi- 

 sphere as counter-clockwise and clockwise in the 

 southern. 



The Work of the Nautical Almanac Office: M. 

 Updegbatf. 



The American Ephemeris and Nautical Almanac 

 is one of five similar publications, and was first 

 issued for the year 1855 at Cambridge, Mass., 

 under the direction of Lieutenant (afterward 

 Rear- Admiral) Chas. H. Davis, U.S.N. The Am- 

 erican Nautical Almanac Office was established 

 in the year 1849, was removed from Cambridge, 

 Mass., to Washington, D. C, in 1866, and after 

 occupying from time to time various quarters in 

 the Navy Department and elsewhere in the city 

 of Washington, was located in the main building 

 of the new Naval Observatory in 1893. During 

 the first forty-eight years the Ah?ianac had four 

 superintendents, and during the remaining eleven 

 years six directors, the title of superintendent 

 having been changed to director in 1893. 



Professor Simon Newcomb, U.S.N., was super- 

 intendent and director for twenty years, 1877 to 

 1897, and during that time there were published 

 under his direction eight volumes of the "Astro- 



