X. MODELS, ETC. 435 



These instruments have been in use since 1845. The Transit is by Ertel 

 Si Sou, and has a focal length of 7 feet 0*4 inch, and an aperture of 5-33 

 (English) inches. The Mural Circle is by Troughtou & Simms, the circle 

 being- 5 feet in diameter. This telescope has a focal length of 5 feet 

 3-8 inches and an aperture of 4.10 inches. It is upon the work of these two 

 instruments that the positions given in the Washington Catalogue of 10,600 

 stars mainly depend. 



Photograph of a Pastel Drawing of the Omega Nebula 



(G. C. 4403), made with the 26-inch Equatorial of the U.S. 

 Naval Observatory, Washington, U.S.A. 



Rear- Admiral C. H. Davis, U.S.N. 



The drawing was made by Professor Holden and M. Trouvelot, and repre- 

 sents the appearance of this remarkable nebula in October 1875. It is fully 

 described in the American Journal of Science for May 1875. There is a 

 probability that changes are going on in the structure of the west end of this 

 nebula, similar to those suspected in the nebula of Orion. 



Photograph of a Pastel Drawing of the Ring Nebula 

 in Lyra (G-. C. 4447), made with the 26-inch Equatorial of 

 the U.S. Naval Observatory, Washington, U.S.A. 



Rear- Admiral C. H. Davis, U.S.N. 



The drawing was made by Professor Holden, U.S.N. It is fully described 

 in the Monthly Notices of the Royal Astronomical Society for November 1875. 

 By close attention a small star can be detected within the ring which must 

 have been much brighter when first seen by Von Hahn before 1800. 



Photograph of a Pastel Drawing of the Planet Saturn, 



made with the 26-inch Equatorial of the U.S. Naval Observatory, 

 Washington, U.S.A. Rear- Admiral C. H. Davis, U.S.N. 



This drawing was made by M. Trouvelot, and is fully described in the 

 Proceedings of the American Academy of Arts and Sciences for 1875. 



Photograph of a Pastel Drawing of the Central part 

 of the Nebula of Orion (G-. C. 1 179), made with the 26-inch 

 Telescope of the U.S. Naval Observatory, Washington, U.S.A. 



Rear-Admiral C. H. Davis, U.S.N. 



This drawing was made from measures by Professor Holden, U.S.N., and 

 M. Trouvelot. It is a preliminary chart of the Huyghenian region, which it 

 is intended to complete. In the photograph the fainter portions of the nebula 

 appear too faint, as compared with the drawing. 



These photographs of instruments and drawings exhibited have been pre- 

 sented to the South Kensington Museum by Rear-Admiral C. H. Davis, 

 U.S.N., on behalf of the United States Naval Observatory at Washington. 



1915. Atlas Coelestis Novus. Stellas per mediam Europam 

 solis oculis conspicua3 secimdurn veras lucis magnituclines e coelo 

 ipso descriptre ab Eduardo Heis D. Math, et Astron. Prof. P. O. in 



Ee 2 



