402 



KNOWLEDGE. 



October, 1910. 



have been made in England or in America, and are 

 at present equally divided between the two countries, 

 the share of each being eight. To Greenwich 

 Observatory belongs the credit of the last of these 

 discoveries, that of the eighth satellite of Jupiter, 

 which was found on a plate taken by Mr. Melotte. 

 The minuteness of the work of "discovery" ma\' be 

 gauged from the fact that it takes, on an average, 

 lour hours to find the image of a satellite on a plate 



1 In 1 hciiiipson equatorial : llir t«iii refractor and reflector. 

 The largest instrument at Greenwich. 



even when one knows where to look for it. In 

 cometary j)hotography the Observator\- has been 

 as successful as the climatic conditions allow: 

 and it possesses a remarkable series of j)hoto- 

 graphs, numbering upwards of one hundred 

 and fifty, of Morehouse's Coiuet. The\- are now 

 awaiting examination in the hope, and with tlie 

 view, of elucidating some of the problems of 

 cometary structure. 



In addition to the multiplii"atioii of obser\'ations 

 which these implements imply, is the additional 

 work done with all the instruments. With the old 

 Transit Circle, set up with such meticulous care In- 

 Airy,* the number of annual observations has in- 

 creased from four thousand to ten thousand a \'ear. 

 W'ith the new .Altazimuth erected by Christie in place 

 of the old, the number of observations has been quad- 

 rupled. The old I-iefiex Zenith Tube, once all but 

 abandoned because the mo\x'ment of the Pole and the 



variations of latitude, due to the imperfect rigidit}- 

 of the Earth, were unsuspected, and seemed to make 

 the instruiuent's obser\-ations all wrong, now does 

 \-aliant and invaluable work. In addition to this, 

 and in addition to its refined work of observation of 

 the Double Stars. Greenwich pursues all the modern 

 investigations which have been imposed h\ the 

 science of Spectroscop}-. Spectroscop\- and Sir 

 William Huggins"s work date from a tiiue anterior 



The transit cuclc : the fundamental instrument at 

 Greenwich. 



to the Christie era, l)ut the greatest advances in 

 .\strophvsics have been made since the general use 

 of the gelatine drv plate ; and the spectroscopic 

 apparatus which Greenwich now uses is due to the 

 initiative ot its Director. 



It remains onl\- to notice that all these new 

 instruments and methods have changed the face of 

 Greenwich Observatory as the spectator sees it. New- 

 domes for protecting the instruments have sprung 

 up ; new libraries, computing rooms, storehouses and 

 workshops have been added, so that (again to (juote 

 Professor Turner) the Octagon Tower, which was 

 the whole Observatory at its foundation in 1876, and 

 remained its chief architectural feature for two 

 centuries, is now rivalled by a stately building of 

 cruciform shape at the south end of the grounds, 

 and the Seven Domes of Greenwich, when seen 

 from a distance, ha\-e the appearance of a small 

 astronomical cit\' set on a hill. 



The contractors for the work were dismayed by Sir George .A.iry's demands for accuracy of adjustment. He insisted 



on pivots accurate to within ;;TrJt,u of an inch. 



