OBSERVATIONS OF LUMINOUS METEORS. 375 



iii the remarks on the process of mapping and projecting them graphically 

 on star charts which have heen offered in the last section regarding them. 

 The following recommendations to observers on occasions of the occu- 

 rence of aerolitic meteors, and of the falls of meteorites, describing the 

 points of information most desirable to be recorded regarding their 

 characters and appearance, have been drawn up at the request of the 

 Committee, to conclude these practical directions, by Dr. Flight. _ 



IV. Detonating, or Aiiwlitic Fireballs.— In recording observations on 

 the passage of a meteor across the sky, the points which it is most desir- 

 able to arrive at are : such data as will allow of our definitely noting the 

 direction of its path and its point of extinction, the duration of the 

 luminous phenomenon, and of individual phases of it, the apparent mag- 

 nitude of the meteor, the luminosity as compared with other brilliant 

 objects, and the changes which it may itself exhibit in this respect 

 during the transit, the duration of the train (or " streak "), and the changes 

 it may undergo before extinction (whether it fade away simultaneously 

 along the entire length, or break up into a chain of luminous fragments) ; 

 also,°in cases where the streak is one of great persistence, the manner of 

 its final disappearance ; again, when the meteor has been observed near 

 the time of sunrise, or sunset, what change it wrought in the appearance 

 of the visible train by the increasing, or waning, light of the sky. The 

 sound attending its passage, if any, and the character of the sound, a,s 

 regards intensity and duration, whether single and well defined, or a series 

 ofminor explosions closely following one another. And finally, the time 

 of appearance, and that of the interval before the explosion is heard. 



While it is barely possible for one observer to record all the data 

 referred to, he should not fail to note such of them as may have come 

 clearly within his observation. Other spectators may have remarked 

 what he may have missed, and their joint observations may enable us to 

 arrive at a complete physical history of the meteor in question. 



It is desirable to determine two. points of the track of the meteor, as 

 far asunder as possible — the points of appearance and extinction are to 

 be preferred— and to indicate the former by reference to some star or 

 constellation which it overlies, and the latter by some object on the 

 horizon against which it is projected. In cases where the meteor is seen 

 in daytime, the data to be arrived at are the point of appearance and its 

 angular altitude. The former may be estimated by noticing what con- 

 spicuous object lies vertically below it on the horizon: a village or a 

 mountain peak. The more distant the object is from the spectator, the 

 more accurate will be the determination of this element of the observation. 

 If objects to which reference can be made should be wanting, the 

 direction may be temporarily noted, and subsequently determined by the 

 aid of a compass-needle. To learn an angular altitude we dare not 

 trust general conclusions, however carefully arrived at ; even experienced 

 observers may be misled in such cases. If a vertical object, say the roof 

 of a house, ' or the top of a tree, happen to lie in the direction under 

 consideration, the observer should approach it till the line of sight of the 

 origin of the course of the meteor skirts the summit of the terrestrial 

 object. The observer has now to determine how far he is removed from 

 the object selected, its vertical height above the plain on which both are 

 situated, and the distance above the ground of his own eye, in order to 

 be in a position to determine the angular elevation of the point of 

 appearance of the meteor, the position of which he desires to ascertain. 



