REPORTS OF ASTRONOMICAL OHSERVATOHIKS. 095 



expediency of eiilarj;inj;- the merulian openings was ackiiowicdgcd; 

 hitherto the ai)ei'tniu !uul only been G inches (0'" 15«). 



At the bogiuiiing of the present century it became necessary to rc- 

 buikl the Observatory, atid the work, continuing until 1811, consisted in 

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

 Observatory propei- and containing halls f»u' the nieridiau instruments, 

 the library, and o1Vk;c, while t!ie western structure was intended for the 

 dwelling-house of the supeiintendent. Jt was in one of these new halls 

 that the first ukhIcI of a mural circle, .") feet (1'" .5) in diameter, con- 

 structed by E. Trougiitox, was placed in 1812. 



The present orgaaization of Green v.ich Observatory dates from a royal 

 statute of 1830. According to 1 he terms of this statute the board of 

 visitors consists of the members of the lloyal Society, the members of 

 the Astronomical Society, and the Oxford and Cambridge professors of 

 astronomy. In 1811: the tirst altazimuth was set u]). It was designed 

 by Airy, and made by Eansome & Merz and Troucjuton & Snnrs, 

 being intended for lunar observations. 



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

 18.")9 for the reception of the equatorial of \V. Si-^iMS, with an object- 

 glass, by G. Merz, having a focal length of Si feet 5 inches (1()'" .5) ; 

 now used for spectroscoiiic work. 



The observations nuule annually at Greenwich have been published 

 regularly since 17G5. In the first volume of this publictation we find tin? 

 first notice of the illumination of the reticulation in a nunidian iustiu- 

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

 Instruments : 



{a) Meridian circle: one; makers, Ransomes & May (engiiuH>rs), 

 TROUGnTON & SIMMS (opticiaus) ; diameter of cinde, 72 inches ; divided 

 to 5' ; read by six microscopes to 0".00 ; four supplementary microscopes 

 for determiuatiou of division errors and occasional use: aperture of 

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

 8.1; magnifying power ordinarily employed, 10") diameters. 



{b') Alt-azimuth : makers, Kansomes& May and W. Sim3IS ; aperture, 

 4 inches. Magnifying i)Ower, 100; diameter of circles, 3 feet, divided 

 to 5'. 



(e) Equatorial instruments : makers, RANSo:\rES & Snnis (engineers) 

 TROUGnTON & SIMMS (opticians), Merz (obje(;tive) ; aperture of object- 

 ive, 12.8 inches; magnifying power of eye-pieces, GO to 1500. {&) Shcap- 

 shanlch equatorial: makers, T. GRUBB,CAUcnoix, (objective); aperture 

 of objective, G^- inches. Kaylor equatorial : maker, T. Cooke, of York; 

 aperture, G inches. ShucJcburyh equator i<( I : makei', Ramsden; aperture, 

 ■4.1 inches. 



(</) ^Spectroscopes : half-prism spectroscope; maker, 11ilgj:r. Direct 

 vision : one, two, or three compound " half prisms" with dispersioiiJS (A 

 to H) of about 18AO, 83°, and 335°. JSingleprism stereoscope: Makers, 

 Trougiiton & SIMMS; one flint prism. 



