ANNUAL RECORD 



OF 



SCIENCE AND INDUSTRY 



187 7. 



ASTRONOMY. 



By EDWARD S. HOLDEX, 



U. S. Natal Observatory, Washington. 



INTRODUCTION. 



The year 1877 will be remembered by the discovery of 

 the two faint satellites of Mars more than by any other one 

 event. A possible satellite of Mars has often been sought 

 for by D'Arrest, Tuttle, and others, but an imagined analogy 

 placed such a satellite or satellites farther from the planet 

 than either of the bodies discovered by Professor Hall. These 

 satellites may be said to be fatal to the analogies ordinarily 

 quoted, and to show how vague a guide these really are. 

 The outer satellite is almost unique in the solar system, and 

 the inner one is quite so, in its relations of distance and mass 

 with its primary. A further account of these will be found 

 in the proper place. 



The changes of spectrum of Schmidt's JVbva Cygni are of 

 great importance, and are certainly not yet understood ; and 

 the same may be said of Dr. Henry Draper's discovery of 

 oxygen in the sun, even the nearer consequences of which 

 have not yet been worked out. 



A 



