MACKIE — ON SPIRAL PLANETARY ORBITS. 



83 



The notion of the resistance of the ether of space to planetary 

 orbital motion, has been passing through other minds besides our 

 own, and since we printed them we have read with much pleasure 

 an article by Professor Henrichs, of Iowa, on the Density, Rotation? 

 and Age of the Planets, in the ' American Journal of Science.' All 

 the old astronomical notions of the old astronomers of the perma- 

 nence of the heavenly orbs and the celestial system, still retained, 

 and too closely and superstitiously adhered to, are based upon 

 and must be based upon erroneous foundations. The permanence 

 and endurance of heavenly bodies, and the perpetual rectification and 

 everlasting persistency of their motions, must be based upon these 

 assumptions: — 1. that space is a vacuum; 2, that a body set in mo- 

 tion in vacuo will continue in motion ad infinitum ; 3, that every 

 form of motion must be an accurate mathematical figure perfectly 

 and absolutely true, such as a circle, an ellipse, a straight line; and 

 lastly, that there must never be any transportation or intercom- 

 mingling of even the merest particles of matter between one world 

 and another, nor the least loss nor the least gain of material from 

 any planet or sun whatever, from the beginning to the end of time. 

 The world at its creation must have been weighed in the balance, 

 and not an ounce nor a feather's weight added to it since. Now we 

 know there is ether in space ; if there were not, the light of the sun 

 would have no material to vibrate upon, and though the sun burned 

 with ten times its glorious brilliancy, all would be darkness here, for 

 jt is scarcely possible to believe that light could travel in an absolute 

 vacuum. We never get, experimentally, a perfect vacuum, pump as 

 hard as we can ; fit the joints of our instrument as close as we may, 

 we never get one. It is always an atmospheric vacuum, a nitrogen- 

 vacuum, a hydrogen- vacuum, an ether-vacuum, — always some resi- 

 due ; never a vacuum at all, however near it may approach, — always 

 some material pnrticles, no matter how expanded, for the vibration of 

 light to thrill along, and this the electric spark and the spectrum- 

 prism will always show. If the ether of space exist, — and astrono- 

 mers who adhere strongest to the old notions admit it, — there must 

 be resistance. The more subtle the ether, the more delicately slight 

 the resistance, but still resistance ; and with resistance comes fric- 

 tion, with friction retardation and the evolution of heat. With re- 

 tardation of orbital motion the diameter of the planet's orbit must 

 be contracted. The world might — most probably would — run round 

 the sun up to the very same line, radiating from our luminary to the 

 same hour, minute, and second, but not to the same spot, but to a 



