THE AUGUST METEORS. 185 



A typical feature of the Perseids is to be found in the streaks 

 which frequently mark their course (Fig. 1), and serve an extremely 

 useful purpose in enabling the directions to be registered with great 

 accuracy. The theoretical velocity of these meteors is thirty-eight 

 miles per second, so that they belong to the swiftest class of such 

 bodies, and, as such, would be individually recorded with much diffi- 

 culty, were it not for the special feature referred to. Their very rapid 

 transient flights would baflie the observer as he stood endeavoring to 

 retain the exact points of beginning and ending ; and in the majority 

 of instances he must absolutely fail to get nearer than a mere approxi- 

 mation. Only in cases where the meteors sped from one star to an- 

 other, or in courses parallel to closely adjoining stars, could the paths 

 be truthfully reproduced on his map. But, fortunately for such inves- 

 tigations, we have no such difficulties to encounter. The phosphores- 

 cent line, almost invariably projected on the sky by the nucleus as it 

 rushes along, remains to guide the eye in fixing its position. It is the 

 authentic signature of the meteor gone before, and during the brief 

 span of its endurance the observer knows how to utilize it. It is sel- 

 dom these streaks last longer than three or four seconds, though in 

 exceptional cases of Perseid fire-balls they have lingered several min- 

 utes. The writer found the average 1"8 second from many observa- 

 tions in August, 1880 ; and the most frequent duration is about two 

 seconds. All the brighter meteors of the shower display them. Mr. 

 Henry Corder, of Writtle, has observed these Perseids with great dili- 

 gence in recent years, and retained many interesting notes of their 

 peculiarities. Of 910 meteors belonging to this system, which he saw 

 in the years 1871-79, .526 were accompanied by streaks. These in- 

 cluded 158 of the first magnitude, only 15 of which were devoid of 

 streaks ; and 243 of the second magnitude, of which 72 were streak- 

 less. Among the smaller members the proportion was larger. He 

 found the brightest meteors were generally pale-green, others orange, 

 etc. 



The luminous streaks, which are known to be the ordinary charac- 

 teristic of these shooting-stars, have acquired a special significance 

 from the fact that by their means the radiant point of the shower is 

 capable of being ascertained with remarkable precision. This impor- 

 tant element, to be reliably determined, must rest upon a large number 

 of accurately recorded tracts, which intersect (on being prolonged 

 backward) at a well-defined position. Many observers have succeeded 

 in finding this from results of more or less value. Mr. R. P. Greg 

 analyzed all the positions estimated prior to 1876, and gave the aver- 

 age at R. A. 44, Dec. 56 north ; and Major Tupman, from a discus- 

 sion of his own elaborate observations in the Mediterranean during 

 the years 1869-'71, derived the point 45J + 56, as the center of 28 

 sub-radiants. Evidently the two results, being founded on a large 

 number of trustworthy records, and agreeing so closely as they did. 



