1891.] on An Astronomer s Work in a Modern Observatory. 403 



fault can be found with it. But these very qualities render it unde- 

 sirable as an observatory. An essential matter for a j)erfect observa- 

 tory should be the possibility to equalise the internal and the external 

 temperature. The site of an instrument should also be free from the 

 immediate surroundings of chimneys or other origin of ascending 

 currents of heated air. Both these conditions are incompatible with 

 thick walls of masonry and tbe chimneys of attaclied dwelling houses, 

 and therefore, as far as possible, I have removed the instruments to 

 small detached houses of their own. But tbe transit circle still 

 remains in the main building, for, as will be evident to you, it is no 

 easy matter to transport such an instrument. 



The two first photographs show the instrument, in one case pointed 

 nearly horizontally to the north, the other pointed nearly vertical. 

 Neither can show all parts of the instrument, but you can see the 

 massive stone piers, weighing many tons each, whidi, resting on the 

 solid blocks 10 feet below, support the pivots. Here are the counter- 

 weights which remove a great jjart of the weight of the instrument 

 from the pivots, leaving only a residual pressure sufficient to enable 

 the pivots to preserve the motion of the instrument in its proper 

 jjlane. Here are the microscopes by which the circle is read. Here 

 the opening through which the instrument views the meridian sky. 

 The observer's chair is shown in this diagram. His work appears to 

 be very simple, and so it is, but it requires special natural gifts — 

 patience and devotion, and a high sense of the importance of his work 

 — to make a first-rate meridian observer. Nothing apparently more 

 monotonous can be well imagined if a man is " not to the manner born.'* 



Having directed this instrument by means of the setting circle to 

 the required altitude, he clamps it there and waits for the star which 

 he is abf)ut to observe to enter the field. This is what he sees. 

 [Artificial transit of a star by lantern.] 



As the star enters the field it passes wire after wire, and as it 

 passes each wire he presses the key of his chronograph and records 

 the instant automatically. As the star passes the middle wire he 

 bisects it with tlie horizontal web, and again similarly records on his 

 chronograph the transit of the star over the remaining wehs. Then 

 he reads otf the microscopes by which the circle is read, and also the 

 barometer and thermometer, in order afterwards to be able to 

 calculate accurately the effect of atmospheric refraction on the 

 observed altitude of the star ; and then his observation is finished. 

 Thus the work of the meridian observer goes on, star after star, hour 

 after hour, and night after night ; and, as you see, it differs very widely 

 from the popular notion of an astronomer's occupation. It presents no 

 dreamy contemj^lation, no watching for new stars, no unexpected or 

 startling phenomena. On the contrary, there is beside him the carefully 

 prepared observing-list for the night, the jDreviously calculated circle 

 setting for each star, allowing just sufficient time for the new setting 

 for the next star after the readings of the circle for the previous 

 observation. 



