230 KKPORT— 1875. 



brevity, introduced ; but it is not thought necessary to use it in the above 

 selected Table of cometary coincidences, where, for greater clearness of de- 

 scription, such points of close approach (or of " appulse " of comet-orbits to 

 the earth's) are simply denoted in the first columns of this Table as being 

 " near " the comet's ascending or descending node. For the general pur- 

 poses of comparison between the probable orbits of observed meteor-streams 

 whose dates and radiant-positions may be hereafter or have already been 

 sufficiently well determined, and those of certain comets whose computed 

 orbits are found to pass, at the points of approach to the earth's orbit, either 

 very near to or at no very remote distance from it, and for convenience of 

 reference in identifying such examples of supposed agreement between 

 meteor-showers and cometary radiant-points as have already been pointed 

 out, the dates and positions of the radiant-points of all the computed comet- 

 orbits intersecting the ecliptic plane within a quarter of the sun's distance 

 inside or outside of the earth's orbit are collected together in two Tables 

 (pp. 232, 234) in the order of dates and of position of the cometary radiant- 

 points above or below the equator, the two lists being arranged for the 

 northern and southern hemispheres respectively, according to the north or 

 south declinations of the computed radiant-points. As these radiant-points 

 were computed by the approximate graphical method devised by Schiaparelli 

 (Entwurf einer astronomischen Theorie der Sternschnuppen, p. 78, §49), the 

 tests which the elaborate calculations of many of the radiant-points bj'' 

 Dr. Weiss supply are employed to check the graphical constructions ; and all 

 the radiant-points originally calculated by Professor Weiss, who takes into 

 account what has elsewhere been omitted throughout in the graphical pre- 

 paration of these Tables (the ellipticity of the orbits of those comets which 

 are known to be periodic, and whose orbits accordingly differ sensibly from 

 parabolas), are included as standards of correct determinations in the present 

 lists. 



In the column of reference numbers at the beginning of the Table the names 

 of discoverers and particulars of meteoric connexion of some periodic comets 

 are added, together with references to other numbers where comets are known 

 or conjectured to be more or less probably identifiable with comets of an 

 older date, although no elliptic figure may haA'c been observed or calculated 

 in the dimensions of their oi'bits. A question sign is added after that of the 

 node or appulse if the elements are uncertain, and the date in the following 

 column is corrected for precessional alteration to the year 1875 from that of 

 the comet's aijparition. The fourth column contains the comet's radius vector 

 or distance from the sun in terms of the semidiameter of the earth's orbit 

 as unit, at the node or point of intersection of the orbit with the ecliptic, 

 unless the appulse replaces the node in the Table, when the comet's distance 

 above (-f-) or below ( — ) the earth's orbit at the point where its radius vector 

 is unify is substituted in brackets (in terms of the same unit as the scale of 

 measurement) for the value of the radius vector. A similar estimate to that 

 afforded by the radius vector in other cases can thus be formed of the degree 

 of proximity in Avhich the path of the comet and the earth's orbit approach 

 each other in such instances at their points of close conjunctions at equal 

 distances from the sun. Thus the comet 18G2 II crossed the ecliptic plane 

 (with retrograde motion, at an ascending node corresponding to the shower- 

 date on Aug. 19th) about 0*03 (or twelve moon's distances) without the earth's 

 orbit ; but, owing to its small inclination, iu approaching nearer to the sun 

 it slightly neared the earth's orbit ; and at a point corresponding in the earth's 

 annual motion to about the 7th of August, it passed only 0-025 earth's solar 



