O PRESIDENT S ADDRESS. 



many to whom the idea of stellar streaming occurred as an ex- 

 planation of outstanding anomalies in proper motion. 



It was left, however, to Kapteyn, and to Kapteyn first and 

 foremost, to place beyond the region of doubt the hitherto vague 

 and uncertified judgments regarding star drifting. 



Those who were privileged to be present at the meeting in 

 Cape Town, in 1905, when Kapteyn dealt with his remarkable 

 discovery of two symmetrical star streams sweeping through the 

 spaces will remember the sensations akin to awe with which thev 

 heard of rivers of stars flowing on and on and on, silent, majestic, 

 irresistible. 



What the nature of this vast movement is, whether in a 

 -traight line, or along the arc of some majestic circle, how con- 

 trolled and how conditioned, no vision can determine accurately, 

 no analysis reveal fully. Kapteyn 's pioneer work has been splen- 

 didly supplemented by the labours of Dyson, Eddington. Boss, 

 Schwarzschild, and Campbell. In the Southern Hemisphere, 

 Hough and Halm have attacked the problem from another direc- 

 tion, that of spectroscopic proper motions. A word of explanation 

 may be pardoned me as to the content of this problem of star 

 gauging, for upon its solution depends our assured conception of 

 the structure and configuration of the stellar universe as a whole. 

 All round us is the firmament of stars. Any movement of our Sun 

 through space will reveal itself in two ways. We shall have a 

 telescopic proper motion of every star near enough to indicate a 

 parallactic displacement, and, second, we shall have a spectro- 

 scopic proper motion of every star in the sky, far or near, which 

 the sun in its journey through space is either approaching or 

 receding from. To these relative movements, due to the sun's 

 motion, we must add the real stellar movements due to each star's 

 own absolute motion. 



Now, if the stars are uniformly distributed in space, and if 

 the sum total of their real proper motions amounts to zero, then 

 a simple application of the laws of probability will yield the 

 direction and the amount of the Sun's motion in space, and, con- 

 sequentlv. the real proper motion of every star near enough to 

 show secular change of position in the telescope, or bright enough 

 to reveal line of sight motion in thie spectroscope. 



But recent investigation has clearly proved that the stars are 

 not uniformly distributed in space. Indeed, one needs the aid 

 of no refined analysis to come to this conclusion. 



A clear night and a pair of seeing eyes are all we need. 



But what neither a clear night nor seeing eyes will reveal, is 

 whether the hazy stretches of misty light seen in the midnight sky 

 are faint stars, because they are far away, or are dimly luminous 

 because they are small suns crowded together. Without doubt, 

 the instruments Halm and Hough have chosen for their attack on 



