

PRESIDENT'S ADDRESS. 11 



representation of the original work. It is specially valuable 

 as showing the different positions of stars 1800 years ago, 

 though doubtless with much less accuracy than at present. 

 Both rotation and variability in the brightness of different 

 portions have been observed in certain nebulae, but a 

 satisfactory theory of the cause of the latter phenomenon 

 is still wanting. The actual distance of a certain nebula 

 (N.G.C. 7662) has been calculated to be 140 light years, 

 which, turned into miles, represents a distance almost too 

 great to realise and requires about 15 figures. The star 

 having the greatest known proper motion, which amounts 

 to 10" per annum, has been found to be a small one of the 

 llth magnitude. Its motion is shown by numerous photo- 

 graphic plates, dating from 1888. Variations in the solar 

 rotation, chiefly periodic, have been observed, and in the 

 early part of February, 1917, one of the largest groups of 

 spots ever recorded was visible. Other large spots occurred 

 at the <-nd of May, 1916. On December 26th, 1915, a small 

 spot appeared in lat. 59.6 S., the highest position ever noticed, 

 the highest hitherto having been only 50.4 in 1846. An 

 unusually fine prominence was seen on May 26th, 1916, 

 which reached to a height of 18' or about 500,000 miles. It 

 has been found that as a rule the melting of the polar caps of 

 Mars is most rapid at timss of great sunspot development, 

 when also solar radiation has been shown to be most intense. 

 The 9th satellite of Jupiter is found to be from 11 to 17 

 miles in diameter, the 7th and 8th baing 17.5 and 18 miles 

 in diameter respectively. Photometric observations of 

 Uranus have revealed a variation in its light to the extent 

 of about .15 magnitude in the course of .451 of a day. This is 

 supposed to be due to its rotation presenting sides of different 

 brightness, as the period agrees fairly well with that derived 

 from other considerations. Many theories which have 

 been accepted as undoubtedly true seem to be in a state of 

 change or modification owing to recent discoveries, and ther? 

 is some reason to think that the Newtonian theory of gravity 

 itself may have to be modified in some respects. Certain 



