35 



that the literature of spectroscopy almost never 

 contains the information we require. The only 

 way to obtain sufficient data is to produce them 

 ourselves, under conditions within our own control 

 and adapted to meet the manifold requirements 

 of the observed astronomical phenomena. More- 

 over, the performace of a few experiments never 

 suffices. It becomes necessary, not only to imi- 

 tate an effect for a given line, or for a limited region 

 of the spectrum, but to extend the observations 

 over the whole range of spectrum available. 



It is easy to see that heavy tasks devolve upon 

 our laboratory staff, both in observing and in the 

 extensive work of measurement and reduction. 

 It is a comparatively simple matter to show that a 

 change of furnace temperature will modify the 

 relative intensities of certain lines; but to measure 

 the changes for the thousands of lines of iron, 

 chromium, nickel, vanadium, and many other 

 elements recognized in celestial objects is a task 

 requiring years of continuous work. So with all 

 of the other effects of pressure, magnetic field, 

 change of potential of the electric discharge, etc. 

 It is evident why the simple beginnings of this 

 laboratory on Mount Wilson have led to larger 

 developments in Pasadena, where heavy electric 

 currents and other facilities are available. 



The intrinsic value of the laboratory results, as 

 distinguished from their usefulness for the inter- 

 pretation of astronomical observations, should not 

 be overlooked. Each investigation is equally 



