256 CARNEGIE INSTITUTION OF WASHINGTON. 



each object the plates covered intervals of 11 years. The older plates 

 were taken by Mr. Ritchey, the later ones by Mr. Duncan. 



These two nebulae show results analogous to those found for M 101 

 in 1916 and for M 33 in 1920. The displacements in all cases seem to 

 correspond better with a motion along the arms of the spirals than 

 with a rotation. The radial components, in the mean, are 39 per cent 

 of the rotational components, while the total displacements agree in 

 direction, within the limits of the measurement, with the arms of the 

 spirals. 



The results now available practically exclude the possibility that 

 they are due to any source of error in the telescope or the measuring 

 instrument, for the photographs were taken partly at the 25-foot 

 focus and partly at the 80-foot focus of the 60-inch reflector, and partly 

 with the Crossley reflector of the Lick Observatory; and, further, 

 they have been measured partly with the old and partly with the new 

 stereocomparator, while some measures have also been made with an 

 ordinary measuring machine, all of which give similar results. 



Accepting the measured displacements as real motions, we find the 

 best explanation of the results in Jeans' s theory, matter being thrown 

 off from two points of a nebula after it has attained a lenticular form. 



Miscellaneous Photographs op Nebulae and Clusters. 



During the year Mr. Duncan has obtained 134 photographs of the 

 following nebulae, clusters, and miscellaneous objects: 



N. C. G. 224, M 31 Andromeda nebula. N. C. G. 4254, M 99 Virginis, spiral. 



N. C. G. 598, M 33 Trianguli, spiral. N. C. G. 4736. M 94 Canum. Ven., spiral. 



N. C. G. 869, h Persei, open cluster. N. C. G. 4872 etc., Comse. Many small nebulae. 



N. C. G. 884, X Persei, open cluster. N. C. G. 5194, M 51 Canum. Ven., large spiral. 



N. C. G. 891, Andromedse, spiral on edge. N. C. G. 5457, 101 Ursse Majoris, large spiral. 



N. C. G. 1952, M 1 Tauri, Crab nebula. N. C. G. 6218, M 12 0phiuchi, globular cluster. 



I. C. 418 Leporia, planetary nebula. N. C. G. 6514, M 20 Sagittarii, Trifid nebula. 



I. C. 423 Orionis, octopus-like nebula. N. C. G. 6523, M 8 Sagittarii. 



N. C. G. 1976, M 42, Orion nebula. N. C. G. 6705, Mil Scuti, open cluster. 



N. C. G. 1977, nebula around c Orionis. N. C. G. 6720, M 57 Lyrse, ring nebula. 



N. C. G. I 434 etc., south of f Orionis. N. C. G. 6822 etc., remarkable group in Sagit- 



N. C. G. 2024, following f Orionis. tarius. 



N. C. G. 2068, M 78 Orionis. N. C. G. 6853, M 27 Vulpeculse, dumb-bell ne- 



N. C. G. 2043, Camelopardalis, pinwheel spiral. bula. 



N. C. G. 2841, Ursae Majoris, spiral. N. C. G. 6946 Cephei, pinwheel spiral. 



N. C. G. 3031, M 81 Ursae Majoris, spiral. N. C. G. 6960 Cygni, network nebula. 



N. C. G. 3184, Ursae Majoris, spiral. N, C. G. 7006 Delphini, globular cluster. 



N. C. G. 3184, Ursffi Majoris, spiral. N. C. G. 7078, M 15 Pegasi, globular cluster. 



N. C. G. 3226-7 Leonis, double spiral. N. C. G. 7293 Aquarii, Harding's helical neb- 



N. C. G. 3242 Hydra;, planetary. ula. 



N. C. G. 3550 Ursae Majoris, many small ne- N. C. G. 7492 Aquarii, globular cluster. 



bulae. N. C. G. 7662 Andromedae, planetary. 

 N. C. G. 4038-9 Crateris, remarkable spiral. 



Dark Markings: Miscellaneous: 



Barnard 72 Ophiuchi, S-shape. The Pleiades. Nova LjTse. 



Barnard 86 Sagittarii. Neptune. Nova Cygni (1920). 



Barnard 92 Sagittarii. Nova Persei No. 2 (1901). 



Barnard 133 Aquilae. Nova Aquilae No. 3 (1918). 



