272 



KNOWLEDGE. 



[Dbcembek, 1901. 



overt-ake the earth in her orbit and move in direct orbits 

 like the comets of short period. 



The obsei^ved motion of certain fireballs and shooting 

 stars is slower than that computed from parabolic 

 velocity. Thus a meteor belonging to the May Aquarids 

 seen on 1900, May 3, traversed a long and nearly 

 horizontal flight of about 155 miles at a velocity of 28 

 miles per second, while the theoretical speed was 40 

 miles per second. Atmospheric resistance must un- 

 doubtedly induce a retai-dation in the velocity, and 

 particularly in those cases where the objects penetrate 

 to low altitudes and encounter the denser air strata. 

 But the observed velocity has been occasionally found 

 less than half that which would be shown by bodies 

 moving in parabolic orbits, and some other explanation 



fully estimated, and the several values were veiy con- 

 sistent with each other, but the speed only amounted to 

 about half that which would have been exhibited by 

 unchecked objects moving in parabolic orbits. Of about 

 five meteors registered during the Perseid epoch from 

 the Lyncid shower at 106° 4- 52°, four were of the swift, 

 streak-leaving class, while the one mentioned above as 

 apparently dii'ected from the same radiant was " very 

 slow " and offered a great distinction to the others. 



The abnoiTnally slow motion found in the two cases 

 named cannot be wholly attributed to atmospheric 

 resistance, for other meteors coming from the same 

 radiants exhibited no signs of similar retardation. 

 When comjiaring obsei'vations of fireballs and dedtxcing 

 their real heights I have been much struck at the 



- _?-^Vi*3.m- — 





iia iq 11^ ttl lol /oJ- lax ff 'j^ f^ ftf ^7 ^.^ ^' 7^ 



h a 



ij io ■'^ S2, St ^ ^^ tfX J^ il, 33 .1^ ly i^ u 



f S- /z f /, J 



seems necessary. There are certainly marked differences, 

 both in the apparent and real velocity of meteors from 

 a common radiant. On 1901, Aug. 10, lOh. 58m., a vei-y 

 slow shooting star was observed at Slough, Farnborough, 

 and Bristol, with a velocity of about 16 miles per second 

 and a radiant at 352° — Uo.f On Aug. 18, 13h. 24m., a 

 shooting star was seen at Slough and Bristol with a 

 velocity of 15 miles per second and a radiant at 

 106° -I- 52°. t In these cases the r ate of motion was cai-e- 



+ The real paths of these objects were independently computed by 

 Prof. Herschel at Slouch, by Lieut. -Col. Tupman at Harrow, and by 

 the writer at Bristol, and tlie resulting velocities were in excellent 

 agreement. Lieut.-Col. Tupiuau has also determined the orbital 

 elements, and finds a periodic time of only 224 days for the Aquarid 

 of August 10, and of 327 days for the Lyncid of August 18, on the 

 assumption that at the great height of 60 or 70 miles the atmospheric 

 resistance is a neghgeable quantity. 



frequency with which the disappearance occurs at an 

 elevation of about 27 or 28 miles. It is comparatively 

 seldom, according to my experience, to meet with a really 

 well-observed fireball or meteor which disappeared be- 

 tween heights of 31 and 42 miles. From the compu- 

 tations made here of 96 fireballs I get the following 

 figures : — - 



Height at 

 dlBappearance. 



Less than 12 miles 

 12 to 21 miles 

 22 to 31 „ 

 32 to 41 „ 

 42 to 51 „ 

 52 to 61 „ 

 Exceeding 61 miles 



Number of 

 Fii-ebalis. 



1 

 19 

 30 

 12 

 19 



!) 



6 



Per- 

 centage. 



10 

 19-8 

 31-3 

 12-5 

 19-8 



9-4 



6-2 



Combining this table with some similar and extensive 



