LUMINOUS METEOR OBSERVED AT GENEVA* 210 



of this month, will allow it to be compared with tho«e ascer- of meteors ds* 

 tained by other observers. This is the only method of ob- 

 taining any accurate ideas respecting the vertical height, 

 course, and nature, of these bodies foreign to our Earth, and 

 the short passage of which cannot be foreseen. 



You have availed yourself of a favourable circumstance, Gmesses at 



to obtain the altitude and azimuth of that luminous object; ****^;'^^'S^>** 



. , . • and disunces 



but It is far from probable, that observers in other situations noi lobede. 



should be able to avail themselves of a similar proceeding: P^'^^^^ on 



and should they report the height of the meteor, without 



having determined it by any instrument, we must expect 



great deviations. 



There is a certain degree of confidence however, to be unless by ex- 

 given to the estimations of men accustomed to appreciated®"^" P^'" 

 their sensations, and compare quantities. If therefore such 

 an observer should say, that he saw the meteor nearly at 

 45°, or at 30°, for example, this might be considered as pro- 

 bably coming pretty near the truth: because we muy pre- 

 sume the ob<erver, measuring in idea the interval from the 

 zenith to the horizon, could pretty well estimate by the eye 

 the half or third of that distance. 



But there is a correction to be made in this estimate, Necessary eor- 

 which is scarcely thought of, but which, in loose obaerva- g*^'^^"^^"^^^ 

 lions of this sort, is in reality of great importance. these, 



The apparent firmament is a skene arch, which may be from the appa. 

 compared to an arc of a circle of about 6o'; (see Smith's ^"^j/"**' 

 Optics, translated by Peztnas, vol. I, p. 117)« If we con- 

 struct a semicircle on a right line, and cut off an arch of 

 about 60° to represent the apparent firmainent, (as in the 

 figure in Smith's Optics), we shall see, that half from the 

 vertical of this apparent firmament answers to about 30° of 

 real altitude, and a third to about 4U°. Now it is easy to 

 perceive the importance of such a correction, if we would 

 obtain any accurate result from comparative observations, 

 and in particular if we attempted to ascertain a parallax. 



In confirmation of this remark I lay before you the ob- Estimation by 



servation of a man possessed of all the faculties calculated ^ observer at 



, . . , . , . * . f. _, Geneva, 



to mature his judgmentin the estimation oi measures. You 



will therv see, that he estimates the height of the meteor 



between 



