NO. 1 6 METEOR-ORBITS IN THE SOLAR SYSTEM — VON NIESSL 3 



the beginning of the observed hmiinous streak is ordinarily not the 

 same as observed everywhere, but that in this respect differences up 

 to large angular arcs and up to hundreds of kilometers in linear 

 measure can occur. We must except the cases with long enduring, 

 sharply marked traces when the observations relate especially to these 

 •and not to the whole orbit. 



In general the orbit may not be deduced by assuming the identity 

 of the indicated initial points of visibility. 



Since the true orbit does not differ appreciably from a straight line, 

 the eye of the observer determines with it a plane which is a section 

 or great circle of the celestial sphere. The so-called apparent orbits 

 observed at different places can therefore be considered as arcs of 

 great circles which, on being produced backwards (in the direction 

 opposite to the course of the meteor), will indicate by their inter- 

 section the apparent radiant. 



The determination of this apparent radiation point depends thus 

 upon the fact that one intersection is given by many great circles that 

 do not coincide but are given by the observations of the same meteor 

 made at many places. 



If now two sets of arcs of orbits are at hand the solution, whether 

 by computation or by graphics, is so simple that it does not require 

 further explanation. The problem is more complicated when numer- 

 ous observations are to be united, and yet it is especially desirable, 

 in fact important, to use a great excess of observations in order to 

 determine the orbits of the great fire balls and meteorites for which 

 we often have less accurate and partly also incomplete material. 

 These are the typical cases to which the following explanations will 

 principally relate. 



The positions at which the planetary path of a large meteor is 

 checked by the resistance of the air (the end of the orbit) is almost 

 always so clearly shown by special phenomena that there is seldom 

 any doubt as to the identity of this point. Ordinarily it is the one 

 single point in the orbit of which this can be assumed with equal 

 probability. Moreover, in reference to it, the near agreement among 

 the observers is practically certain and occasionally the research is 

 favored by observations of sound or even by the finding of pieces of 

 fallen fragments of the meteorite. 



The most accurate possible determination of the location and 

 altitude of the end of the meteor's track forms in general a very 

 important and generally indispensable prehminary to all further 

 investigations. 



