SCIENCE. 



361 



This would require only to suppose the form of the 

 force changed, in quantity proportionate to the quantity 

 of matter, by passing through it, so as to act against 

 particles in proportion to size, and to some other features, 

 of which velocity and kind are elements, instead of in 

 proportion to weight only, as before. 



We cannot blame Lesage for overlooking the incon- 

 sistency of the utter disappearance of so much dynamic 

 energy as his theory requires, because in his day the idea 

 of the conservation of energy had not grown up ; and it 

 was a great, a sublime, grasp of thought, to conceive of a 

 relation of mechanical action which was parallel in its 

 nature to that utter, that bewildering, mystery of gravi- 

 tation, which seemed as if it could only be due to the 

 fiat or action of Creative Energy itself, acting forever 

 and everywhere de novo ; yet, at the same time, al- 

 ways with an absolutely steady and measured force and 

 relation to quantity ot matter, to distance in space, and 

 to length of time, which indicated kinship in character 

 to the other proximate and not ultimate forces of 

 nature.* 



But we cannot so easily overlook the failure of those 

 who have later considered this theory to notice this 

 great dynamic hiatus, and to follow it up to some con- 

 clusion. 



These facts, stated, of the comets, of the planets, and 

 of meteorites, indicate very clearly that there is a pecu- 

 liar propulsive force acting outward from the sun. 



And this force is of the general nature required to fill 

 this hiatus. 



Can we further de'ermine anything of its nature? 



We have already seen that it seems to act upon some 

 kinds of matter in preference to other kinds ; and that 

 there seems to be different varieties of this selec'ive dif- 

 ference caused by and in some proportion to velocity. 



This last is a curious feature. How can velocity act 

 to increase the action of a force on one kind of matter 

 more than on another ? Can any of the facts of ordinary 

 knowledge give us any indications? 



If we subject" different substances to dry friction, 

 electro-static disturbance is produced ; the d fferent 

 kinds of substance will be acted upon differently, and 

 perhaps the difference may be increased by the increase 

 of the friction. 



Now the condition shown in the comet is very much 

 like that of an electrified body. But we must not jump 

 to conclusions without examining the attendant condi- 

 tions which would govern the facts. 



We can suppose that the velocity of a body or assem- 

 blage of bodies through the ether, required to transmit 

 light, or through a space containing other sfray particles 

 of matter, might produce a friction that would set up in 

 it an electrified state ; and which would be increased by 

 increase of the velocity. 



We can suppose that the light and electrical bodies, 

 and the heavy metals would be electrified to different 

 degrees ; or at least that there would be different electric 

 states produced, 



And we can suppose that THE FORCES ACTING out- 

 ward FROM THE SUN ACT ON PARTICLES IN SOME PRO- 

 PORTION TO THEIR ELECTRIFIED STATES ; and that on 

 striking an assembly of particles it is reflected from their 

 members, something like light is, in a great number of 

 directions, which tends to drive them outward, and, in a 

 less degree, to disperse them apart, as shown by the tail 

 of the comet. 



These suppositions show that the requirements which 

 observation seems to call for have parallellisms within 



* We may believe that under the whole face and system of Nature 

 there is an ultimate creative force which acts immediately each instant, to 

 keep alive, to measure, and to guide, ali of the actions and reactions tak- 

 ing place ; but that is a conclusion and not a " knowledge. " If it is true, 

 yet it chances that the character of the action is such that we recognize 

 all actions and reactions as taking place in chains having equality of links 

 and certain peculiarities we call laws ; which constitute proximate 

 causes. 



our knowledge, and indicate the course of new enquiries. 



As a result of these and other considerations we may 

 be led to infer that the growth of the solar system has 

 been affected by such causes. That the heavy metals 

 have, in coming into it, taken positions at last, very 

 much dependant upon their weight and kind, in which 

 respect the Earth, Venus and Mars, in their great interior 

 masses, may represent the region of iron, while Mercurv 

 may represent the region of still heavier metals, and the 

 outer planets the great mass of lighter substances; the 

 average or mean distance of a body from the sun being 

 governed inversely as the square of its mean velocity. 



Thus a comet and its tail may become the missing link 

 in astronomy and in science. 



CORRESPONDENCE. 



\Tke Editor does not hold himself responsible for opinions expressed 

 by his correspondents. No notice is taken 0/ anonymous communi- 

 cations.} 



To the Editor of " SCIENCE ": — 



I have been interested in reading Mr. Rock's account of 

 his observation of the great Comet on the 6lh of July. 

 On that evening the comet was hidden at this Observa- 

 tory by clouds until about ten o'clock, local time, when Mr. 

 Wilson went into the dome to observe its position with 

 the eleven-inch refractor. He soon returned, however, 

 and called my attention to the remarkable appearance of 

 the nucleus. ( went to the dome and from that time un- 

 til three o'clock we alternately examined the Comet, mak- 

 ing sketches and measures. The fan had its usual 

 appearance, but when first observed a bright red jet pro- 

 jected from the nucleus into the dark region on the side of 

 the nucleus opposite the fan. This jet was totally differ- 

 ent in appearance from those usually seen. It was at first 

 straight and in brightness rivalled the nucleus itself ; in 

 fact at the first glance it seemed to form one with the nu- 

 cleus. On a closer inspection, however, I saw that it had 

 a transparent appearance but still intensely bright and 

 red. The next glance showed that there was a dark line 

 separating it from the nucleus. Mr. Wilson had already 

 called my attention to this dark line before I went to the 

 dome. During the first few minutes a decided change 

 took place. The jet seemed to separate and form a nu- 

 cleus of its own, so that for a time the comet appeared 

 double ; gradually, however, the detached portion grew 

 fainter, until when last seen, at about three in the morning, 

 although plainly visible, it was no brighter than the fan- 

 shaped appendage on the opposite side of the nucleus. I 

 noticed the band of light which Mr. Rock speaks of as 

 connecting the " node " with the nucleus, and mentioned 

 it to Mr. Wilson at the time, but this afterwards disap- 

 peared, leaving a separate mass floating like a cloud in 

 the dark region opposite the fan. 



There can be no question that a great outburst took 

 place in the comet on that evening, nor that a portion of 

 the nucleus became detached. The phenomenon was 

 watched very carefully for five hours and I think I could 

 hardly be mistaken in what I saw. ORMOND Stone. 



Cincinnati Observatory, Jtdy 19, 1881. 



To the editor of " SCIENCE." 



In Mr. Rachel's reply, in No. 52, to my letter in No. 

 47 of "Science," he appears to enteitain a different 

 conception of the law of gravitation from that which I 

 supposed to be usually entertained by astronomers. As 

 there may be many others who share his view, it seems 

 advisable to give a more detailed exposition of what I 

 think was Sir Isaac Newton's own conception, and is 

 that of many more recent as ronomers. 



Newton's law of gravitation is that " every particle of 

 matter in the universe attracts every other particle with 



