434 



NATURE 



[Mar. 28, 1872 



characterises it "as an elegant and probably original contribution 

 to the theory of the orbits of bodies moving freely in space, and 

 acted on only by their mutual attractions." 



I come now to give some account of Signor Schiaparelli's 

 principal discovery of the law of identity of meteors and comets, 

 and of the observations and reflections which led him to that 

 result, as contained in a series of letters to Father Secchi in the 

 year 1S66. 



It appears from these that Signor Schiaparelli's study of this 

 subject received a great impulse from his own observation of the 

 meteors which fell on the nights of the gth, loth and nth of 

 August, 1866. He states that he was then confirmed in the 

 opinion expressed three years before, that, of the meteors which 

 usually fall on those nights, a great number are distinguished by 

 their starting nearly all from one point. And, from the spas- 

 modic fall of these meteors — more sometimes falling in one 

 minute than in the next quarter of an hour — he inferred that 

 their distribution in space must be very unequal. He also ob- 

 served that those stars proceeding from one point were all of a 

 fine yellow colour, and left behind them a fugitive but very 

 sensible track ; whilst the other meteors, proceeding from various 

 points, offered every variety of colour and form. Hence he con- 

 cludes that the meteors form a number of rings, and become 

 visible when the earth traverses their orbit, as if shooting forth 

 from one point in the sky. And he remarks that the observa- 

 tions of M. Coulvier-Gravier, and Professor Heis, and of our 

 own countrymen, Professor Herschel and Mr. Greg, have shown 

 that these radial points occur in every quarter of the heavens ; 

 therefore these rings or orbits must possess eveiy possible degree 

 of inclination to the ecliptic. 



He then proceeds to inquire how such a mass of cosmical 

 matter could become accumulated in the Solar System. This 

 system seems to consist of two classes — the planets, characterised 

 by but little eccentricity of orbit, slight variation of the plane of 

 the orbit, exclusion of retrograde motion, and a tendency to take 

 the form of a sphere (deviating from it only so much as is neces- 

 sary to preserve the equilibrium of the body) — these characteristics 

 applying also to the secondary systems, with the exception of the 

 satellites of UraiiKs. The second class consists of cometary 

 bodies, which are under no law as to the planes of their orbits, 

 or the direction of their motions. .The point most remarkable 

 about them is the extreme elongation of their orbits, most of 

 which are described in stellar space ; which seems to show that 

 they did not form part of our system when that was first con- 

 stituted, but are wandering nebula; picked up by our sun. 



Signor Schiaparelli further observes that the velocity of the 

 solar system through space has been shown by Otto Struve and 

 Airy to be somewhat similar to that of the planets i-ouml the 

 sun. Now if a nebulous body or comet in motion were to come 

 within the action of tlie sun, it would go round the sun at such 

 an immense distance from us, that it would remain invisible. 

 Two circumstances might bring it within our range of vision — 

 first, if the comet met the sun in almost a direct line ; and 

 secondly, if it were travelling in a direction parallel to the sun's 

 motion. 



If we suppose a cloud of cosmical matter formed ot particles 

 so minute and so widely separated as to possess scarcely any 

 mutual attraction, to be brought within the power of the sun's 

 influence, each particle would pursue an elliptic orbit of its 

 own. Those particles which differed most in the plains of 

 their orbits would however possess nodes in common., and,^in 

 consequence, the particles as they approached the sun would 

 necessarily approach each other, and when separating again, 

 after passing the node, would at their perihelion passage be 

 still very much nearer than they were when brought first 

 within the sun's attraction. Those particles which, lying in 

 the same plane, presented a wide angle with respect to the sun, 

 would form ellipses, the planes of which would be identical ; 

 though the positions of the major axes would diverge, and, as a 

 result, the particles at their perihelion would pass in nearly the 

 same orbit, but at different velocities, the originally foremost 

 particle being overtaken by those behind it. Again, those 

 particles which, being in the same plane, were also in the same 

 line with regarel to the sun — their separation consisting in the 

 variation of their distance from the sun — would form ellipses in the 

 same plane, and having a major axis in the same direction, liut 

 of different lengths, — the orbit of the particle nearest the sun 

 being described 'oithin that of the farthest particle, the result of 

 which would be a difference of speed, and an ever-widening dis- 

 tribution of the particles along the whole of the orbit. This 



reasoning is illustrated, in the second letter to Father Secchi, by 

 a series of diagrams and figures ; and then Signor Schiaparelli 

 proceeds to give a recapitulation or summary of his principal 

 propositions thus : — Celestial matter may be divided into the 

 following classes, 1st, fixed stars ; and, agglomerations of small 

 stars (resolvable nebulre) ; 3rd, smaller bodies invisible except 

 when approaching the sun (comets) ; 4th, small particles com- 

 posing a cosmical cloud. This last class probably occupies a 

 large portion of the celestial spaces, and the motion of these 

 dust-clouds may be similar to that of the fixed stars. When 

 attracted by the sun they are not visible unless they receive an 

 orbit which is an elongated conic section. 



Whatever may have been the original form of the cloud, it 

 cannot penetrate far into our system without assuming the form 

 of an elongated cylinder passing gradually into a stream ot 

 particles. The number of such streams seems to be very great. 

 The particles are so scattered tliat their orbits may cross each 

 other without interruption, and may possibly be always changing 

 like the beds of rivers. The stream, after passing its perihelion, 

 will be more diffuse than before ; and, when passing a planet, 

 may be so violently affected as to separate or break up, and even 

 some particles may assume quite a new orbit and become inde- 

 pendent meteors. 



Thus meteors and other celestial phenomena of like nature, 

 which a century ago were regarded as atmospheric phenomena 

 — which La Place and Olbers ventured to think came from the 

 moon, and which were afterwards raised to the dignity of being 

 members of the planetary system — are now proved to belong 

 io t\ie stellar regions, and to be, in truth. Jailing stars. They 

 have the same relation to comets as the asteroids have to the 

 planets ; in both cases their small size is made up by their greater 

 number. 



Lastly, we may presume that it is certain that falling stars, 

 meteors, and aerolites, differ in size only and not in composition ; 

 therefore we may presume that they are an example of what the 

 universe is composed of. As in them we find no elements 

 foreign to those of the earth, we may infer the similarity of com- 

 position of all the universe — a fact already suggested by the 

 revelations of the spectroscope. 



Signor Schiaparelli further pursues the subject in another and 

 later paper, published in No. 1629 of the Astronomische Nach- 

 riehten, entitled " Sur la Relation qui existe entre les cometes 

 et les etoil'^s filantes. " In this communication he refers to the 

 letters to Father Secchi above referred to, in which he had endea- 

 voured to bring together all the arguments in favour of the 

 opinion of an analogy between the mysterious bodies known as 

 shooting stars and comets. 



Signor Schiaparelli, in this paper, proceeds to state that he is 

 prepared to afford to this analogy a large amount of probability, 

 since there is no doubt that certain comets, if not all, furnish the 

 numerous meteors which traverse the celestial spaces. In proof 

 of this Signor Schiaparelli quotes from a paper of Prof Erman, 

 in which he has pointed out the method of obtaining a complete 

 knowledge of the orbit described by a system of shooting stars, 

 when the apparent position of the point of radiation and the 

 velocity through space of the meteors is knowir 



Assuming from the necessity of the case that the orbit of the 

 August meteors must be an elongated conic section, Signor .Schia- 

 parelli employs the method of Erman to calculate the parabolic 

 orbit of those bodies ; taking right ascension 44° and north decli- 

 nation 56" for the position of the point of divergence, according 

 to the observations made in 1863 by Prof. A. .S. Herschel. And 

 he proceeds to give the following elements, assuming the maxi- 

 mum of the display of 1S66 to be August 10, iS hours. Com- 

 paring these elements of the orbit of the August nicleors with 

 those of the orbit of Comet II. 1862, calculated by Dr. Oppol- 

 zer, he exhibits the following remarkable coincidence in each 

 element : — 



Elements of the Orbit Elements of the Orbit 

 of the Aug. Meteors. of Comet II, 1862 



Perihelion Passage 23 July, 1862 22'9 Aug., 1862 



Longitude of Perihelion 

 Ascending Node 

 Inclination 

 Perihelion Distance 

 Revolution Period 

 Motion 



Although the time of revolution of the August meteors is still 



