INTRODUCTION 



first, by inanely assuming that it got started without 

 power, and, secondly, by interpreting its manifold con- 

 cordances as just happy fortuities. As a very abbrevi- 

 ated list of the host of things about our solar system 

 which astronomers confess their inability to explain, in 

 spite of the aid of these factitious assumptions, let me 

 quote again from Dr. Young's book (Gen'l Astr., p. 566) : 



In the present state of science many of the questions thus 

 suggested seem to be hopelessly beyond the reach of investigation, 

 while others appear like problems which time and patient work 

 will solve, and others yet have already received clear and decided 

 answers. In a general way it may be said that the condensation 

 and aggregation of rare field masses of matter under the force of 

 gravitation; the conversion into heat of the (potential) ''energy 

 of position" destroyed by the process of condensation; the effect 

 of this heat upon the contracting mass itself, and the radiation 

 of energy into space and to surrounding bodies as waves of light 

 and heat these principles contain nearly all the explanations that 

 can thus far be given of the present state of the heavenly bodies. 



We see that our planetary system is not a mere accidental ag- 

 gregation of bodies. Masses of matter coming haphazard to- 

 wards the sun would move as comets do, in orbits, always conic 

 sections to be sure, but of every degree of eccentricity and in- 

 clination. There are a multitude of relations actually observed in 

 the planetary system which are WHOLLY INDEPENDENT OF GRAVI- 

 TATION AND DEMAND AN EXPLANATION. 



1. The orbits are all nearly circular. 



2. They are all nearly in one plane (excepting the cases of 

 some of the little asteroids). 



3. The revolution of all is in the same direction. 



4. There is a curiously regular progression of distance (ex- 

 pressed by Bode's law, which, however, breaks down at Neptune) . 



5. There is a roughly regular progression of density, in- 

 creasing both ways from Saturn, the least dense of all the planets 

 in the system. 



As regards the planets themselves, we have : 



6. The plane of the planet's rotation, nearly coinciding with 

 that of the orbit (probably excepting Uranus). 



7. The direction of the rotation the same as that of the 

 orbital revolution (excepting probably Uranus and Neptune). 



8. The plane of orbital revolution of the satellites coinciding 



nearly with that of the planet's rotation. 



