WRIGHT— RECENT SPECTROSCOPIC OBSERVATIONS. 521 



by some others, chiefly by Sir Norman Lockyer, who regard it 

 as out of harmony with the well-known laws of gaseous equilib- 

 rium. According to Lane's law a star, assuming it to be a gaseous 

 mass, should grow hotter while contracting as the result of the loss 

 of its heat.- This rise in temperature should continue until the 

 material, through increased density, ceases to be a perfect gas, after 

 which the temperature will fall. According to this conception a 

 young star would be comparatively cool, and therefore, red ; with 

 increasing age it would grow hotter, achieve a maximum, and then 

 cool ofif. There would be a succession of colors corresponding to 

 temperature. Now all of the spectra of the red stars are not alike, 

 nor are those of stars of the other groups, and in order to accom- 

 modate the spectral sequence to his hypothesis Lockyer has divided 

 the red, yellow, and white stars into two groups which I shall for 

 simplicity distingiush by means of subscripts. The red stars are 

 the extremes of this system, the Red^, according to Lockyer, being 

 the youngest and the Red„ the oldest of all the stars. Next to them 

 come the corresponding groups of yellows and whites. I have at- 

 tempted to diagram these two systems in a very elementary way by 

 means of these curves (Fig. 2), in which time is measured from left 

 to right, and temperature vertically. The hypothesis first referred 

 to is represented in the figure on the left. Here we start with the 

 hottest of all stars, those of the Wolf-Rayet or Class O group, and 

 with falling temperature follow through the course of a star's life. 

 The second hypothesis is outlined in the right-hand figure. These 

 two diagrams are inadequate to represent all the views, and^ modi- 

 fications of views that are held in one quarter or another. They 



2 It has been pointed out by Schuster (Astrophysical Journal, 17, 165, IQ03) 

 that Lane's law concerns itself with the temperature of the star's interior, 

 while what we observe is the temperature at the surface. It is not certain 

 that there is a simple relation between the two, since the surface temperature 

 of a radiating body represents merely a balance between the rate of radiation 

 and the rapidity with which heat can be supplied from the interior to make 

 good the loss. If the transfer from within is effected mainly by convection 

 the readiness with which it takes place will depend upon the force of gravity, 

 that is to say upon the mass and dimensions of the star, as well as upon the 

 temperature of its interior. It is therefore extremely doubtful to what extent 

 the inferences from Lane's law should be expected to harmonize with the 

 observations of the surface temperatures of stars, to which we are limited in 

 our investigations. 



