434 ASTRONOMICAL OBSERVATORIES. 



A statute of 1765 confirmed the right of supervision vested in the 

 royal society and exercised by the board of visitors. In 1770 two re- 

 volving domes were constructed upon the turrets, and these have served 

 as models for all revolving turrets since constructed. In 1772 the first 

 achromatic object glass ever used at Greenwich was attached to the south 

 quadrant. In 1779 the expediency of enlarging the meridian openings 

 was acknowledged; hitherto the aperture had only been 6 inches 

 (0.15'"). 



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

 build the observatory, and the work, continuing until 1811, consisted in 

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

 observatory proper, and containing halls for the meridian instruments, 

 the library, and office, while the western structure was intended for the 

 dwelling house of the superintendent. 



The present organization of Greenwich Observatory dares from a 

 royal statute of 1830. According to the terms of this statute the board 

 of visitors consists of the members of the Eoyal Society, the members 

 of the Astronomical Society, and the Oxford and Cambridge professors 

 of astronomy. 



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

 1859. 



Instruments : 

 {a) Meridian circle : One ; makers, Ransomes & May (engineers), 

 TEOuaHTON & SIMMS (opticiaus) ; diameter of circle, 72 inches ; divided 

 to 5' ; read by six microscopes to O.OG" ; four supplementary microscopes 

 for determination of division errors and occasional use: aperture of ob- 

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

 magnifying ]>ower ordinarily employed, 195 diameters. 



{b') Altazimuth: Makers, Ransomes & May and W. Simms; aperture, 

 4 inches. Magnifying power, 100 5 diameter of circles, 3 feet, divided 

 to 5'. 



(c) Equatorial instruments : Makers, Eansomes & Simms (engineers), 

 Tr'oughton & Simms (opticians), Merz (objective) ; aperture of ob- 

 jective, 12.8 inches ; magnifying power of eye-pieces, 60 to 1500. (c') 

 SheajysJianlc's equatorial: makers, T. Grubb, Cauchoix (objective); 

 aperture of objective, 6.^ inches. Kaylor equatorial : maker, T. Cooke, 

 of York; aperture, 6 inches. IShnclhurgh equatorial : maker, Ramsden; 

 aperture, 4.1 inches. 



{(1) iSi;)ec<ros('Oj?cs ; Half -prism spectroscope; maker, Hilger. Direct 

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

 to H) of about 18i°, 83°, and 335°. Single prism stereoscope : Makers, 

 Trougiiton & SIMMS ; one flint prism. 



(e) Photometer : Airy's double-image micrometer; makers. Trough- 

 ton & Sim MS. 

 (/) Chronograph : IMakers, E. Dent & Co. 



