November, 1013. 



KNOWLEDGE. 



405 



From a photograph,* by De la Baume Pluvinel Alcala de Chisverl, Spain, August joth, 1903, 



Figure 419. Prominences that can be seen by means of an ordinary telescope only during an eclipse, but which are 

 shown at all times when a telescope is armed with prisms of wide dispersion. 



* Horizontal Refractor and Coelostat. At. 0.153m. ((>"). F. L. 11.880m. (38' llj".) Exp. 2 sees. 



From a photograph by G. XV. Ritchey, Mount Wilson Observatory, 

 February gth, iqto. 



Figure 420. Owl Nebula in Ursa Major (N.G.C. 3587) 



showing the central star, the bilateral symmetry, and the 



concentric appearance that would occasionally be a late 



stage in the third body produced by a graze of suns. 



Fiom a photograph by G. IV. Ritchey. Mount Wilson Observatory, 

 July 2nd-4th, 11)10. 



Figure 421. The Nebula in Cygnus (N.G.C. 6992), show- 

 ing details brought out by the camera which are too 

 faint directly to affect the human eye. 



I 



