MOUNT WILSON OBSERVATORY. 



221 



The conditions of seeing (on a scale of 10) and the wind velocity are added 

 for purposes of reference: 



These data have all been taken from the meteorological and observing 

 records kept by Mr. Hoge. 



RESEARCHES ON NEBULA. 

 Dibect Photography. 



Numerous photographs, mainly of nebulae and nebulous areas, have been 

 made with the 100-inch and 60-inch reflectors. Among the objects of especial 

 interest photographed by Mr. Hubble, reference may be made to the following: 



N. G. C. 5253, in which the nova Z Centauri appeared in 1895. The nebula is not a true 



spiral, but resembles M 82 or N. G. C. 4214. 

 I. C. 1295. This is a faint planetary of the ring form about 2' in diameter. The central 



star is estimated as of about the 14th magnitude. 

 R Aquarii. In addition to the faint exterior wisps previously known, a close envelope of 



bright nebulosity has been found to exist around this star, which probably gives 



rise to the bright nebular lines recorded on spectrograms. The exposure times 



have ranged from 3 seconds to 3 hours. 



Mr. Duncan has given especial attention to extended areas and regions 

 where dark markings are present. Among his photographs are the following: 



Barnard Nos. 92 and 93. These are dark areas outlined against a star-cloud in Sagittarius. 

 The photograph shows much faint luminous nebulosity not recorded hitherto. 



Barnard No. 152 in Cepheus. A dark marking projected against a background of stars 

 with no certain evidence of bright nebulosit}'. 



N. G. C. 7000, southern portion. This is the well-known North America nebula. A 

 great amount of detail, both dark and bright, is shown in the regions bordering on 

 the "Carribean Sea." The central and western portions of the "Sea" seem to be 

 devoid of bright nebulosity, and the star density is less than one-tenth of that within 

 regions of such nebulosity. In this respect the similarity to that found in I. C. 434 

 south of f Orionis is striking. 



Mr. Humason has made photographs of the following large spiral nebulas, 

 which will be used for measurements of internal motions: N. G. C. 598, 2683, 

 4395, 4400, 5055, 5194, 5457, 6946, 7217, and 7331. 



Several photographs of the Andromeda nebula have been made by Mr. 

 Humason and Mr. Lundmark in continuation of the search for novas in this 

 object. One nova, No. 21, was discovered by Mr. Humason. A number of 

 other objects have been photographed with the two reflectors; in particular, 

 the moon and Jupiter, by Mr. Pease, and several of the older novas by Mr. 

 Lundmark. 



