108 UNIVERSITY OF MISSOURI BULLETIN 



Besides these large non-luminous bodies, we find scattered 

 throughout space, both inside the solar system and outside, an 

 immense number of cold bodies which range in size from small 

 itars down to small stones, and even to the so-called cosmic 

 dust, of which I shall say more later. Some of these bodies 

 get into the earth's atmosphere, where their great velocity pro- 

 duces so much heat by friction and compression of the air that 

 they become luminous for a short time as meteors or "shoot- 

 ing-stars," and either fall to the ground or are burned up. 



Finally, we have the peculiar objects known as nebulae. 

 Some of these are great irregular masses of gaseous matter, 

 so large that the solar^ system would be lost in one of them ; 

 but most of them show a curious spiral structure, with bright 

 star-like masses scattered through them. 



RELATION TO OTHER SCIENCES 



These different classes of celestial objects present many 

 different problems, some of which will be stated later. But 

 first a few words may be said about the relation of astronomy 

 to the other sciences. Astronomy has no peculiar laws of its 

 own. It is merely the application of the laws of other sciences, 

 particularly physics and chemistry, to those parts of the uni- 

 verse that we cannot reach with our hands or subject to delib- 

 erate experiment. 



The older astronomy was largely included under the sub- 

 title celestial mechanics, a study of the motions of the solar 

 system which, as the name indicates, is really an application of 

 the most fundamental laws of physics treated by a highly 

 mathematical method. In this study, the law of gravitation 

 is assumed, and also Newton's three laws of motion. From 

 these, knowing the dimensions of the earth and the angular 

 positions of the sun, planets, etc., the actual positions and 

 motions of all the members of the system, for any time, are 

 worked out. As a matter of fact, we are indebted to astron- 



