STELLAR SYSTEMS AND NEBULJS. 211 



Since 1890 nebular photography has been 

 pursued by Max Wolf in Germany, and by 

 E. E. Barnard and J. E. Keeler in America. 

 Wolf's photographs of the constellation Cygnus 

 brought out the close connection between the 

 stars and the extensively diffused nebulosities 

 discovered by him. In 1901 Wolf discovered 

 a " nebelhaufen " or cluster of nebulse, and in 

 1902 published a catalogue of 1528 nebulae 

 round the pole of the Galaxy, showing them 

 to be systematically distributed. Keeler made 

 his memorable observations with the great 

 36 -inch reflecting telescope, which was con- 

 structed in England many years ago by 

 Common. It afterwards passed into the hands 

 of Mr Crossley of Halifax, who presented it to 

 the Lick Observatory. With this great instru- 

 ment Keeler commenced to take photographs 

 of the heavens. On one occasion he photo- 

 graphed a well-known nebula, and on develop- 

 ing the plate was surprised to find seven new 

 nebulae besides that which he had photographed. 

 On another occasion he exposed a plate to a 

 nebula in Pegasus. He was amazed to find 

 altogether twenty -one nebulae included in the 

 photograph. To give another instance, a plate 

 directed to the constellation Andromeda con- 

 tained no fewer than thirty-two nebulous objects. 



