536 



SCIENCE 



[N. S. Vol. XXXTV. No. 877 



Harvard, and it is hoped that arrangements for 

 their regular measurement will soon be completed. 

 Note on the Ellicott Astronomical Instruments: 

 A. B. Douglass. 



These five instruments are novr on permanent 

 exhibition in the U. S. National Museum at Wash- 

 ington. They were partly made by Ellicott be- 

 tween 1780 and 1790 and were all used by him 

 between that time and 1820. The zenith sector, 

 six feet in focus, is suspended by its objective end. 

 The eye end carries an arc, divided to degrees, 

 which passes beneath a plumb line. The fractions 

 of degrees are read by a micrometer. This is the 

 type of instrument by which Bradley discovered 

 aberration and nutation and with which the flat- 

 tening of the earth's figure was first determined. 

 This telescope itself was made by the Eittenhouse 

 brothers in Philadelphia before 1784 and is a copy 

 of the instrument used in locating Mason and 

 Dixon's line. This instrument was used in loca- 

 ting the point where the boundary between the 

 United States and Canada touches the St. Law- 

 rence Eiver. Bradley 's original sector with its iron 

 tube and mounting is now in the Royal Observa- 

 tory, Greenwich. The small zenith sector, 20 

 inches in length, was used as a substitute for the 

 larger in much boundary work. 



The "transit and equal altitude" instrument 

 was used in laying out the boundaries and avenues 

 of the city of Washington, and many state boun- 

 daries. It is the type used in much surveying 

 work in the eighteenth century. Instruments of 

 this type may also be seen in the American Philo- 

 sophical Society at Philadelphia, at Harvard Uni- 

 versity and in the Museum of the BufEalo His- 

 torical Society. 



The quadrant is the oldest type of measuring 

 telescope and is likely to be the oldest of this 

 collection. A similar instrument of larger size is 

 at Harvard University. There are many in the 

 European Science Museums. 



The four-foot telescope was made by W. and S. 

 Jones, of London. It was used for longitude work 

 by observations of Jupiter's satellites. 



The metal work of these instruments is entirely 

 of brass and, except for two of the smaller lenses, 

 all are in excellent condition. 

 Seport of the Committee on PhotograpMc As- 



trometry : F. Schlesinger, chairman. 



The report of this committee took the form of a 

 symposium. The chairman outlined briefly what 

 had been done previously on the determination of 

 star places by photography. The experiments of 



Pickering, Hagen, Hirayama, Triimpler, Donner 

 Jacoby, Cookson, Eoss and Pluvinel were briefly 

 described. The chairman then presented the fol 

 lowing resolutions, which were adopted at a meet 

 ing of the committee held in New York on AprU 

 23, 1911, when there were present Messrs. H, 

 Jacoby, E. C. Pickering, H. N. Eussell, E. Schles 

 inger, E. W. Brown and S. A. Mitchell, the last 

 two by invitation: 



RESOLUTIONS 



The Committee on Photographic Astrometry of 

 the Astronomical and Astrophysical Society of 

 America is strongly of the opinion that photo- 

 graphic methods can be applied successfully to 

 absolute as well as to differential determinations 

 of star positions, thereby gaining the advantage 

 of independent observations with instruments of 

 entirely different characters. The committee 

 recommends : 



1. That the north and south polar points be de- 

 termined by means of trails secured with a fixed 

 telescope according to the method originally pro- 

 posed by Pickering and developed by Jacoby. 



2. That these polar points be connected with a 

 number of regions on the equator and that the 

 latter be connected among themselves by the 

 methods proposed by Turner on pages 427 et seq.. 

 Vol. LXXI., Monthly Notices of the Boyal Astro- 

 nomical Society. 



3. That the method proposed by Pickering (to 

 be published soon in the Harvard Circulars) be 

 used to determine the positions of stars to the 

 twelfth magnitude in the immediate vicinity of 

 the equator. 



4. That the differential method proposed by 

 Turner (page 422, Vol. LXXI., Monthly Notices 

 of the Boyal Astronomical Society) be employed 

 to ascertain the positions of stars referred to the 

 standard regions mentioned under 2. 



The committee is further of the opinion that the 

 degree of accuracy attainable by these methods 

 can not be predicted with certainty, but can be 

 found only by accurate trial. 



The symposium then continued with the reading 

 of papers (given above in abstract) by E. C. Pick- 

 ering and H. N. Eussell; and various aspects of 

 the general problem were discussed by Messrs. C. 

 L. Doolittle, Littell, Eussell, Tucker, E. C. Picker- 

 ing, Frisby and the chairman. 



e. h. curtiss, 

 University of Michigan 



Editor and Acting Secretary for 

 the Twelfth Annual Meeting 



