REPORTS OF ASTRONOMICAL OHSKRVATc >h'Ii:S. 09.5 



expediency of eiilargino- the meridian openings was acknowli'ilg,.,! ; 

 liitherto the apertnie had only been inches (()'" 15-). 



At the beginning of the present century it became necessary to re- 

 bnihl the Observatory, and the work, continuing until ISll. e(»nsisted in 

 the construction of two rectangular buildings, the eastern one being tiie 

 Observatory proper and containing halls for the meridian instruments, 

 the library, and oflice, while the western structure was intended Ibi- the 

 dwelling-house of the superintendent. It was in one of these new hulls 

 that the first model of a mural circle, 5 feet (1"' .5) in diametei, eou- 

 structed by E. Trougiiton, was placed in 1812. 



The present organization of Greenwich Observatory dates from a royal 

 statute of 1830. xVccording to the terms of this statute the board of 

 visitors consists of the members of the Royal Society, the meud^ers of 

 the Astronomical Society, and the Oxford and Cambridge i)rofessors of 

 astronomy. In 1844 the first altazimuth was set up. It was designed 

 by Airy, and made by Ransome & Mekz and TKOUGnxox & Simms, 

 being intended for lunar observations. 



As a finishing touch, the immense dome to the southeast was built in 

 1859 for the reception of the equatorial of W. Simms, with an object- 

 glass, by G. Merz, having a focal length of 34 feet 5 inches (10'" .5); 

 now used for spectroscopic work. 



The observations made annually at Greenwich have been pultlished 

 regularly since 1705, In the first volume of this publication we lind the 

 first notice of the illumination of the reticulation in a meridian instru- 

 ment by means of the axis of the spy-glass. 

 Instruments : 



(«) Meridian circle: one; makers, Ranso:\ies & :\Iav (engineers), 

 Troughton & SIMMS (opticians) ; diameter of circle, 7i' inches ; divided 

 to 5' ; read by six microscopes to 0".0G ; four supplementary microscopes 

 for determination of division errors and occasional use: aperture of 

 objective, 8.1 inches; for observations of the sun, aperture eiuployed, 

 8.1; magnifying power ordinarily employed, 105 diameters. 



{b') Alt-akmutU : makers, 1Unsomes& May and ^^^ Simms : ai)erture., 

 4 inches. Magnifying power, 100; diameter of circles, 3 feet, divided 



to 5'. 



(c) Equatorial instruments: makers, IUnsomes & Snois (engnieers) 

 Troughton & Simms (opticians), Merz (objective) ; aperture of object- 

 ive, 12.8 inches; magnifying power of eye-pieces, 00 to 1500. (c') Shcap- 

 slianVs equatorial : makers, T. Grubb, Cauchoix, (objective) ; aperture 

 of objective, 0^ inches. Naylor equatorial: maker, T. Cooke, ol \ork; 

 aperture, G inches. ShucUuryh equatorial : maker, Kamsden ; upertuiv, 



4.1 inches. ^\■ t- 



Ul) Spectroscopes : half-prism spectroscope; maker, Uilger. Direct 

 vision : one, two, or three compound " half j.risms" with dispersions (A 

 to H) of about 18AO, 83°, and 335^. Single-prism stereoscope: ^hikers, 

 Troughton & Simms; one flint prism. 



