MOUNT WILSON OBSERVATORY. 257 



The photographs of M 31 (Andromeda Nebula) include 17 plates 

 of about 1 hour's exposure taken primarily for detecting novse. This 

 purpose was also held in view in photographing the other spirals. 

 A 9-hour exposure on M 31 with the 100-inch telescope was made 

 to show as accurately as possible the form of the nebula and to serve 

 for a future study of internal motion. 



Plates of N. G. C. 1952 (M 1), 2403, 3031 (M 81), 4254 (M 99), 4736 

 (M 94), 5194 (M 51), 5457 (M 101), 6514 (M 20, Trifid), and 6946 were 

 taken for the purpose of studying possible internal changes by com- 

 parison with earlier plates. An hour's exposure on the Ring nebula 

 with the 100-inch telescope shows certain details which do not seem 

 to appear on other photographs, notably a radial structure in the 

 winding streamers. 



The following objects were found to possess special interest: 



(1) The bright and dark nebulae near f Orionis. The photograph of 

 I.e. 434 brings out with great prominence the dark cloud, Barnard 33. 

 There is evidence of four distinct types of nebulosity in the region. 



(2) N. G. C. 4038-9. A small bright spiral of extraordinary form, 

 already noticed by Mr. Hubble on a plate made by hun with the 10- 

 inch Cooke lens. Photographs with the 100-inch telescope show the 

 central part in detail, and, in addition, two faint curved streamers of a 

 length four or five times the diameter of the bright part of the nebula. 



(3) N. G. C. 1977. A well-known nebula whose details are well 

 shown on a plate taken with the 100-inch reflector. 



(4) A region in Coma Berenices with N. G. C. 4872 central, in which 

 Curtis has counted 249 small nebulae in an area 38' by 39' on a plate 

 made with the Crossley reflector. On a plate of 4 hours' exposure 

 with the large reflector Mr. Duncan has counted, within a circle 30' 

 in diameter, 319 nebulae, 115 stars, and 206 faint objects of unde- 

 termined character. 



(5) The dark markings, Nos. 72, 86, 92, and 133 of Barnard's cata- 

 logue, as well as No. 33 near f Orionis, afford striking evidence of the 

 obscuration of stars by intervening masses. It is hoped that the 

 photographs of these objects may be of future use for detecting motion 

 in the obscuring masses or in the stars near their edges by the disap- 

 pearance or emergence of some of the stars. 



(6) N. G. C. 6822. This appears to be a remarkable group of stars 

 and small nebulae, with probably some diffuse nebulosity. Two of the 

 small nebulae resemble comets with bifurcated tails. The longer of 

 two exposures was made under poor conditions and the images are 

 not good. A still longer exposure, wdth good seeing, is needed. 



From a study of the above photographs, Mr. Duncan has obtained 

 the following results: 



1. Three novae, Nos. 18, 19, and 20, were discovered in the Andro- 

 meda nebula. 



