106 UNIVERSITY OF MISSOURI BULLETIN 



in chemistry, or the laws of electrodynamics, laws which we 

 believe hold at any place throughout the universe and will 

 continue to hold throughout all time. On the other hand, 

 astronomy, geology, and the study of evolution, which I will 

 call the historical sciences of nature, apply these very general 

 laws to the study of great changes which may be very slow, 

 but extend over immense periods of time. We might say that 

 students of physics, chemistry, and experimental biology study 

 nature's fixed habits, while students of the historical sciences 

 dig up her dark past, pry into her origin and antecedents, and 

 finally hazard shrewd guesses as to what she will look like 

 and be like a thousand years hence, or a million years, or a 

 billion years. 



This classification must not, of course, be taken too 

 seriously ; for, on the one hand, physics and chemistry them- 

 selves are sometimes concerned with slow, evolutionary 

 changes which so far as we know are never reversed ; and, 

 on the other hand, astronomy has contributed not a little to 

 our knowledge of fundamental laws. Still, in the broader 

 outlines, the natural sciences do group themselves naturally 

 into these two classes. 



DEFINITION OF ASTRONOMY 



Astronomy is one of those sciences which are to a large 

 extent, though not exclusively, historical The best definition 

 I can give of the general subject is this : Astronomy is the 

 study of the motions and positions of masses outside our 

 earth, their physical and chemical nature, and the changes that 

 occur in them over great periods of time. It is also some- 

 times concerned with certain phenomena that occur on the 

 earth itself, such as the aurora borealis, and the earth's mag- 

 netism, which are certainly either caused or strongly affected 

 by the action of the sun. But these phenomena may better 

 be regarded as belonging to geophysics, a branch of physics. 



