724 



SCIENCE, 



[N. S. Vol. XI. No. 280. 



league in our fellow member, "W. L. Elkin, 

 who spent some time at the Cape Observa- 

 tory, carrying on with Gill the work of the 

 new instrument. It was one of the happy 

 results of this co-operation that the Yale 

 University was equipped with the finest 

 heliometer that had then been made, and the 

 instrument placed in the hands of Gill's co- 

 worker. This is the only instrument of the 

 kind that has yet been mounted on this side 

 of the Atlantic. 



The result of Gill's enterprise is that, at 

 the present time, the parallaxes of perhaps 

 a dozen stars of the southern celestial 

 hemisphere have been determined with 

 greater general precision than has been at- 

 tained in the case of any corresponding 

 number in the northern hemisphere. One 

 conclusion from this work is of a nature 

 to excite universal interest. The second 

 brightest star in the heavens, Canopus, al- 

 most as bright as Sirius, has no measurable 

 parallax. What must be the actual size 

 and brilliancy of a star, which appearing to 

 us as bright as Canopus is yet so enor- 

 mously distant as to defy the most refined 

 methods of determining its annual paral- 

 lax ? We can only answer with confidence 

 that it is thousands of times the brightness 

 of the sun. Whether we should say 20,- 

 000, 10,000 or 5000, no one can decide. 

 What adds to the singularity of the result 

 is that this case is by no means unique. 

 Eigel and Spica, both of the first magni- 

 tude, are also beyond our range of measure- 

 ment even with the most refined of instru- 

 ments. 



One prominent feature of the astronomy 

 of our time is the initiation of international 

 co-operative enterprises to carry on such of 

 its researches as require to be conducted on 

 a large scale. One of these enterprises 

 was organized by our medallist. His ex- 

 perience in determining the solar paral- 

 lax from observations of Mars and Juno 

 led him to point out the advantages offered 



by near approaches of the minor planets 

 generally to the earth for the determina- 

 tion in question. 



lu the course of a little more than a year, 

 from the summer of 1889 to the autumn of 

 the year following, there were to be three 

 favorable approaches of these planets to 

 the earth. An arrangement was made 

 with the observatories of the world which 

 had good heliometers in use, and were will- 

 ing to engage in the work, to make the re- 

 quired observations. The labor involved 

 in carrying out the whole plan in the best 

 waj' was very great. The mere making of 

 the observations was a simple matter com- 

 pared with the subsequent reductions and 

 investigations. The first step in the proc- 

 ess was a determination, made with all 

 possible precision, of the positions of the 

 stars of comparison. Not only observers 

 who used the heliometer, but all others who 

 were willing to engage in the work took part 

 in this branch of it. Then it was neces- 

 sary to derive the best possible elements of 

 motion of the three planets. The question 

 how to discuss the observations so as to 

 obtain results which should be as free as 

 possible from the necessary errors in the 

 elements was another important considera- 

 tion. 



The entire work appeared in 1897-98 as 

 Vols. VI. and VII. of the Annals of the 

 Cape Observatory. An examination of 

 these magnificent volumes will give a better 

 conception than anything that I can say of 

 the amount of research devoted by Gill to 

 this investigation. It is impossible within 

 the limits of the present report to give even 

 an abstract of their contents. We must 

 therefore limit our notice to the general 

 statement already made. It should, how- 

 ever, be mentioned in this connection that 

 the discussion of the observations of one 

 of the planets. Iris, was especially taken in 

 charge by the collaborator whom I have 

 already mentioned. Dr. Elkin. 



