OBSERVATIONS OF LUMINOUS METEORS. 45 



attentively. Meteoric showers composed principally of very smaU shooting- 

 stars are confined to the parts of the heavens immediately surrounding the 

 radiant-point ; while those consisting of large meteors spread far from the 

 centre of divergence, the meteors (apparently from their brightness) being as 

 plainly visible when they are seen by transverse as when they are seen fore- 

 shortened by very oblique vision. Meteor- showers of the former kind are 

 called "contracted"; and of the latter kind "extended" (stretta; larga). The 

 foregoing are the principal terms employed by Professor Schiaparelli in de- 

 scribing the meteor-showers of which the positions of the radiant-points have 

 now been published. The explanation of the phenomena of " diffuse " and 

 " multiple " radiant-points is ingeniously supplied by Professor Schiaparelli 

 in the following manner. A very small nebular mass of meteoroids or of 

 cometoids having been deflected from its original parabolic (or very excen- 

 tric) into an orbit of moderate period round the sun by the attraction of some 

 powerful planet in its path, the foremost and swiftest particles of the stream 

 produced by this disturbance gradually gaining, and the slowest losing 

 ground on the central particles of the mass, an elongated form of the mass is 

 gradually assumed directed along the line of the meteoric orbit. The dif- 

 ference of velocity, or of periodic time, between the foremost and hindmost 

 particles of the row is sufficient to ensure the gradual lengthening of the line, 

 until the foremost particle joins with the last in forming a continuous ring or 

 wreath of meteoric substance closing the orbit of the original meteoric clond. 

 Should the two ends, before meeting each other (as must usually be the case), 

 have undergone different pertui'bations from the action of the planets, in- 

 stead of exactly overtaking the retreating end, the foremost end of the wreath 

 will overlap it, and the meteor-stream will begin to assume the form of a 

 spiral curve of a single coil. When the foremost end has gained two revolu- 

 tions upon the retreating one, a spiral of two coils wiU be produced ; and 

 continuing this process during many revohitions gained by one end of the 

 coil upon the other, the wreath of meteoroids, without losing its continuity, 

 wiU at last form an endless hoop, or belt, of many strands overlying and 

 interlacing with each other in as many convolutions as the fastest particles 

 have gained revolutions in their course upon the slower ones. The direction 

 and velocity of the particles in one of the strands wiU also differ as widely as 

 their positions from those of particles in a neighbouring strand, and the whole 

 wreath, without ever losing its perfect continuity from end to end, will cross 

 and recross itself in constantly going and returning waves. In these stages 

 of transformation a meteoric stream woiild si;ccessively exhibit the characters 

 of double and multiple radiant-points. Supposing the same process to con- 

 tinue,, and new perturbations of the stream to be constantly deflecting par- 

 ticles fi'om the front or rear into different courses, these particles overtaking 

 each other at the point where the earth passes through the stream would 

 produce the mixed assemblage of radiant-points and of dii'ections of the 

 meteors of the August shower, which give it the character of multiple or of 

 diffuse radiation. In the following list of radiant-points those marked with 

 an asterisk (*) were described in the last Eeport (1870, p. 98) ; those at the 

 end of the list are not included by Prof. Schiapai'elli in his present list, which 

 only represents the most important radiant-points observed, at present, in the 

 first half of the year. In the cases where their identity with radiant-points 

 in Heis's list, or in that of the British Association t, is suggested by Pro- 

 fessor Schiaparelh, the position and duration of those radiant-points are 

 added for comparison in the same columns of the Table. 



t Eeport for 1868, p. 401 et seq. 



