438 



Anniversary Meeting. 



[Nov. 30, 



The Report on the results of the total Solar Eclipse of 1875, announced 

 in my last year's Address as being drawn up by Mr. Lockyer, is now in 

 our hands. 



The Harvard College Observatory (U.S.). — During my recent visit to 

 the United States, I was for a short time a guest at the Cambridge 

 Botanic Garden, and consequently in close proximity to the fine Obser- 

 vatory of Harvard College, to which I paid several visits, being most 

 kindly received by Professor Pickering, successor to the distinguished 

 astronomer, ~W. C. Bond. The system carried out in this observatory is 

 known to British Astronomers to be so productive of good results that 

 I felt sure that some account of it would be acceptable to the Fellows 

 of the Royal Society ; and I therefore availed myself of Mr. Pickering's 

 good offices to obtain a few particulars. 



The current work of the Observatory is threefold, and consists of obser- 

 vations with the 15-inch equatorial, with the 8-inch aperture meridian 

 circle, and communication of true time-signals to the public. 



The principal work of the equatorial is photometrical, an instrument 

 having been devised by the Astronomer by which two stars may be com- 

 pared directly without using an artificial star as an intermediate step 

 in the measurement. By this means the relative brightness of the 

 components of numerous double stars, including some having only 

 very faint components, as also the relative brightness of the satellites of 

 Jupiter and Saturn, has been determined. 



At the time of my visit Prof. Pickering was engaged in a special study 

 of the newly discovered satellites of Mars, one of which, the outer, I had 

 the satisfaction of observing through the equatorial. Their brightness he 

 had determined by three very ingenious methods : — 1st, by comparison 

 with an image of Mars shining through a very minute circular hole placed 

 at the focus of the telescope ; 2nd, by comparing the satellite with a 

 minute image of Mars formed in the field of the large telescope by a small 

 auxiliary telescope ; 3rd, by reducing the light of the inner satellite by 

 one, two, or three plates of microscope-glass, until its brightness was 

 equal to that of the outer satellite. Of these methods the second showed 

 that the outer satellite does not partake of the red colour of Mars. 



The meridian circle was, or had lately been, in use for the following 

 purposes : — 1st, the determination of the position of all stars brighter 

 than the 9th magnitude contained in the zone 50°-55° N. ; 2nd, observa- 

 tions of Mars during the opposition of last summer for the solar parallax ; 

 3rd, observations of a list of composite stars, at the request of Mr. Gill, 

 for determining the solar parallax by means of Ariadne ; 4th, prepara- 

 tions are being made for the determination of the absolute position 

 of a catalogue of stars, independently of all previous observations, and, 

 5th, for the publication of a catalogue of polar stars observed in 1872- 

 1873 ; 6th. with the assistance of the U.S. Coast Survey, a beginning 



