Popular Science Mo)if/il!/ 



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Above: The build- 

 ing complete, up to 

 the covering of the 

 dome. This is fur- 

 nished with a sys- 

 tem of shutters 

 which with the 

 double wall permit 

 an even tempera- 

 ture to be main- 

 tained in the interior 

 of the building 



Above: The iron 

 framework of the 

 walls. Horizontal 

 ribs are attached 

 in pairs both to the 

 outer and inner 

 edges of the up- 

 right beams, thus 

 forming a double 

 wall with an inter- 

 mediate air-space 



The permanent 

 concrete pier at Vic- 

 toria. The ends of 

 the polar axis are 

 supported on steel 

 castings which are 

 bolted to the 

 heads of the piers 



having already been captured. It is also 

 extremely valuable for spectroscopic work. 

 A long exposure is required even with the 

 great forty-inch Yerkes refractor to olilain 

 the spectrogram of a star of the fourth 

 magnitude. This is much reduced at Mt. 

 Wilson by using the short focus sixty-inch 

 mirror, not only on account of the larger 

 size, but also because the loss of light 

 caused by reflection is much less than that 



suffered by a ray of light in passing through 

 the thick lenses of a large refractor. 



Recently, a great deal of attention has 

 been paid to the study of the spectra of 

 nebulae, and some extraordinary results 

 have been obtained. It has been found 

 that some of them show evidences of rota- 

 tion, a most important fact in its bearing 

 on the e\olu(ion of star s\\stcms, if it 

 can be established by photography. 



