101 
nebulz, and the photograph confirms in general outline the obser- 
vations of Herschel and Lord Rosse, but there is no indication of 
the filamentous projections shown on one of the drawings. On the 
other hand, the central star inside the ring is conspicuous on the 
photograph though not shown on the drawings. 
The next photograph (Pl. vi.) is that of the crab nebula, M. 1, 
in the constellation Taurus. This nebula isin R. A. 5 h. 28 m., 
decl. N. 21 deg. 57m. ‘The scale is 8 seconds of arc to 1 millime- 
ter, and the field is 24 minutes of arc in diameter. The photo- 
graph was taken with the twenty-inch reflector, on February 2, 1892, 
and an exposure of three hours. In Lord Rosse’s drawing, which 
is familiar as a popular illustration, the nebula somewhat resembles 
a pineapple, with hair-like appendages ; but the photograph shows 
it to be irregular, oval in outline, with a deep indentation on the 
following side, and immediately opposite to this is a protuberance 
of faint nebulosity. The nebula, generally, is very bright and 
granular in structure, with patches of unequal density involved, and 
the outer margin is faint and ill-defined. 
Next is the photograph (Pl. vii.) of the spiral nebula, M. 51 
Canum. This nebula isin R. A. 13 h. 25 m., decl. N. 47 deg. 45 
m. ‘The scale is 8 seconds of arc to 1 millimeter, and the field is 
24 minutes of arc in diameter. It was taken with the twenty-inch 
reflector, April 28, 1889, with an exposure of four hours. This 
nebula is the most striking of the spiral form, and the published 
drawings of it by Lassell and Lord Rosse are, perhaps, the best 
known and in outline are in fair agreement with the photographs. 
Both the drawings, however, fail to give an adequate idea of the 
real structure of this remarkable object, which is here correctly 
depicted for the first time. The stars and condensed patches of 
nebulosity follow closely all the whorls of the nebula, and are strik- 
ingly seen on the photograph, though only imperfectly shown on 
the drawings. 
Next is the photograph (PI. viii.) of the nebulae, M. 81, 82, and 
a nebulous star in Ursa Major, with centre in R. A. 9h. 46 m., 
decl. N. 69 deg. 39 m. The area of the sky included is about 1 
deg. 16m. by 1 deg. 4 m. The scale is 16 seconds of arc to 1 
millimeter. The photograph was taken with the twenty-inch 
reflector, March 31, 1889, with an exposure of three hours and 
thirty minutes. The nebula south is M. 81, which is on this pho- 
tograph shown for the first time to be a spiral with a dense nucleus. 
