SPECTROSCOPE AND STUFF OF COSMOS 351 



displacement of the lines of the spectrum, the difficulties which 

 the latter involves, the extraordinary delicacy of observation 

 required, might equally leave the results open to doubt. Their 

 substantial concurrence that is, that the average speed of a 

 hundred stars reckoned by the one method and a hundred more 

 by the other, is not vastly different brings a high degree of 

 assurance. 



Some day or other the concurrence of these two methods 

 may result in a reckoning yet more sublime that is, the orbits 

 of the stars. It is obvious at a glance that the spectrograph 

 registers only the part of stellar motion that lies directly in the 

 line of sight ; while, on the other hand, of proper motions we can 

 know nothing, save that part of the motion which lies at right 

 angles to the line of sight. If stars could be found having both 

 a large radial motion and a large proper motion, likewise a 

 measurable parallax, it would then be possible to estimate their 

 actual speed, and to plot their paths as well. 



Obviously, however, such a condition could not obtain. If 

 the apparent motion were large, the spectral displacement 

 would be small, and vice versa, so the one or the other would be 

 too minute for registry, unless perchance the speed were pro- 

 digious and the placing of the star just right for such observa- 

 tion. This is a problem of the future. It is clear that if a 

 long series of observations could show, for example, that either 

 the apparent or radial motion was growing greater or growing 

 less, here at least would be a slender basis from which some 

 sort of inference might be made. 



In following the disclosures of the spectroscope, especially 

 in its amazing invasion of the invisible, we shall see that some 

 stellar orbits have been found, not of the sort we have been 

 considering, but quite another. Meanwhile, we are now in a 

 position to sum up man's long endeavours to orient himself 

 and his world amid the cloud of stars. The effort is considerable. 

 The mind grasps with ineffectual fingers a vivid realisation 

 of the teachings of the new time. Distances, figures, lose all 

 meaning in their vastness. They leave only a blur. 



Let us try a little to sharpen the image. 



