ASTEONOMICAL PHENOMENA AND PEOGEESS. 



position of its orbit, the most suitable for obser- 

 vation. 



The Planetary System ; Questions relating 

 to its Origin, and its probable Stability. In 

 an article entitled " The Density, Eotation, and 

 Eelative Age of the Planets " (Amer. Jour, of 

 Science, 2d series, vol. xxxvii. date of May, 

 1864), Prof. G. Ilinrichs, of the Iowa State 

 University, examines the doctrine of the " Sta- 

 bility of the Solar System." This doctrine 

 he characterizes as a hypothesis merely. Ad- 

 mitting the existence of an ethereal medium 

 filling space, he proceeds to examine the places 

 and characteristics of the planetary bodies; and 

 is led to the conclusion that a displacement of 

 their orbits, such as would be the effect of the 

 resistance of the supposed medium, has oc- 

 curred and will continue to go on, the tendency 

 being to the ultimate extinction of the system. 

 He remarks that " the absence of positive signs 

 of resistance in the observed motion of the 

 planets, does not prove its non-existence; for 

 if the earth approaches the sun by 10 feet every 

 year, this resistance could not be said to be 

 nothing yet, assuming Kepler's third law as 

 applying to the same planet in different dis- 

 tances, we easily find that the year would be 

 shortened only one second in a thousand years, 

 by this resistance ! " 



The author endeavors to show that, as in the 

 geological examination of terrestrial strata, so 

 we can determine the relative ages of the celes- 

 tial strata the planets and their moons in- 

 ferring this, it would appear, from the com- 

 parative amounts of deviation or dislocation 

 exhibited in their present actual orbits, from 

 a certain regular or mathematical order (such 

 as that expressed in the law of Bode or Titius), 

 which it is assumed should characterize their 

 intervals. He argues that the actual distances 

 of the planets successively from the sun, show 

 a higher age for the exterior over the interior 

 planets, in about the ratio of three to one; 

 that, as marks of increasing age, it will be 

 found that the nearest satellites have ap- 

 proached their primaries ; that the entire 

 system of orbits becomes gradually closer; and 

 that the regularity and symmetry of distances 

 disappears more and more. Among the author's 

 conclusions are, that the satellites of Jupiter, 

 not less than the primary planets, exemplify 

 the law that relative age increases with distance 

 from the central body ; that in an increasing 

 irregularity, as should be trne, the lunar world 

 of Saturn shows as older than that of Jupiter, 

 and that of Uranus as still older ; that the views 

 of the planetary ages arrived at are in harmony 

 with the nebular hypothesis, and are further 

 confirmed by a consideration of the densities 

 of the planets ; while the hypothesis just named 

 finds support also in the law of their rotation. 

 Finally, he supposes that the lost translatory 

 force of the planetary bodies may be converted 

 into magnetism. 



In the 89th volume of the Journal last quoted 

 (dates of January and May, 1865), Prof. Hin- 



richs has an article entitled " Introduction . to 

 the Mathematical Principles of the Nebular The- 

 ory, or Planetology." In this he discusses at 

 length, and, as in the former, from both physi- 

 cal and mathematical considerations, the grand 

 hypothesis the original conception of which is 

 credited alike to Kant and Laplace which af- 

 firms the origin of the solar systemin a diffused 

 or nebulous matter primarily filling its space, 

 this matter having from the first or becoming 

 affected with a movement of rotation, and its 

 subsequent behavior being such as must result 

 through the agency of various attractions and 

 of heat. In the course of this discussion, the 

 author claims to have established what is sub- 

 stantially a new law of the planetary and 

 lunar distances while he also admits its simi- 

 larity to the law of Titius, and speaks of it as 

 comprehending and correcting the latter 

 namely: that " the intervals between the aban- 

 donment of the different orbs of the same sys- 

 tem are equal ; " or, in other words, that the 

 planetary distances correspond to equal inter- 

 vals of time. He finds in the investigation now 

 considered a general confirmation of the views 

 of the preceding paper, and supposes that, of four 

 successive cosmical days or ages (the characters 

 of which he traces), the fourth corresponds with 

 the present. With some other physicists, he 

 anticipates a period when all the planetary 

 bodies of our system will have fallen into the 

 sun ; and when the aggregated mass will remain 

 as a mere " cosmic fossil," but in itself as sus- 4 

 ceptible of instructive investigation as is some 

 fossil shell in the hands of the geologist of our 

 time ! 



In the 38th volume of the same Journal (July, 

 1864), Prof. D. Kirkwood, of the Indiana State 

 University, has a paper " On Certain Harmo- 

 nies of the Solar System," in which he treats of 

 the rotations of the planets, their distances, &c., 

 and the mean distances of the periodic comets. 

 He argues that, granting an ether, having the 

 properties of a material fluid, it must undergo 

 condensation about the sun and other large 

 bodies ; and that, either from its existing in 

 the primitive solar spheroid, or rejecting the 

 nebular theory from the gradually extending 

 influence of the solar and planetary motions, 

 the ether itself must have acquired a move- 

 ment of rotation about the sun in the ame 

 direction with that of the planets. , Even ad- 

 mitting, then, the supposed ether though there 

 are physicistsjpho doubt both its existence 

 and the necessity for any such medium still, 

 its resistance to bodies moving in orbits of 

 small eccentricity and in the direction of the 

 sun's rotation, must be considered an infin- 

 itesimal quantity. Another and more brief 

 paper by the same writer, on the planetary 

 distances, appears in the Journal quoted, for 

 January, 1865. 



Mr. -D. Trowbridge, in the course of a long 

 article upon the " Nebular Hypothesis" (Amer. 

 Jour, of Science, November, 1864, and Jan- 

 uary, 1865), coincides in the conclusion of Prof. 



