TRANSACTIONS OF THE SECTIONS. 13 



dieted by him, tte centre of a total eclipse of the sun actually swept over this di- 

 strict. The Astronomer Royal then explained how Thales was able, by the aid of 

 the Saros, or period of 18 years 15 days and 8 hours, to predict the eclipse ; and 

 then, if the pre\-iously-observed eclipse at the beginnino' of this cycle occurred in 

 the morning (which agi-ees with calcidation), the odd 8 hours would ensure that 

 this one woidd occm- in the afternoon (which also agrees with calculation), and the 

 eclipse might really be predicted, as was recorded. He then pointed out how cal- 

 culation from the same Tables led us to the time and circimistances of the eclipse 

 of Agathocles, when the Grecian fleet escaped out of the harbour of Syracuse ; also 

 to the darlmess, which, no doubt, was an eclipse, which was stated to have taken 

 place when the Persian army entered Larissa or Nimrud. 



On the Resistance of the Ether to the Comets and Planets, and on the Botation 

 of the latter. By J. S. Sttjaet Glennie, M.A. 

 This paper was an application to the motions of the comets and planets of the 

 following theorem, on the hypothesis, favom-ed or adopted by Encke and Ponte- 

 coulant, of a medimn whose resistance is inversely as the square of the distance from 

 the Sim. According as the resultant of the resistance to a revolving and rotating 

 body passes or not through the centre of gravity, will it affect the revolution or the 

 rotation of the body. 



Some Considerations on M. Haidinger's Communication on the Origin and 

 Fall of Aerolites. By U. ^P. Q-r^g, F.G.S. 



M. Haidinger and Dr. Laurence Smith differ in then- opinion as to the cause and 

 origin of the blackish-colom-ed crust observed in almost all meteoric stones ; the latter 

 conceives that they were thus coated previous to their entering the confines of the 

 earth's atmosphere ; the former much more reasonably alleges that it has been caused 

 by simple supei-ficial fusion after the meteorite has entered the atmosphere, either 

 by resistance to the air causing heat, or by the superheated ah- surrounding the 

 stony matter of the fireball itself. Dr. Smith seems to have been misled by 

 circumstances presented on the fall of some very large stones in Ohio, May 1, 1860, 

 which evidently at the time of their fall could not have been very hot. But he 

 seems to have overlooked the fact stated by Haidiuger, that in larr/e stones (espe- 

 cially) the internal parts must affect the temperatm-e of intei-planetary space, and 

 tend almost instantaneously to efface the very superficial heat caused by the sudden 

 fiising of their exterior. 



M. Haidinger and Dr. Smith both agi-ee in thinking that meteorites enter oui* 

 atmosphere more commonly in groups or "flocks " of small fragments, than as a 

 single and larger mass. This seems to me opposed both to fact and probability. In 

 the case of the celebrated fall of meteoric stones at L'Aigle in Normandy, in 180-3, 

 April 26, though it is quite true that nearly 3000 stones fell (the major nmubernot 

 larger than walnuts, and the largest only seventeen pounds), yet we must bear in 

 mind that but one single fireball was seen previously to the bmsting and fall of the 

 meteorite. The stones presented iiTegular shapes, chiefly angular, with the edges 

 slightly rounded, and all similarly covered with a crust. Surely it is more natural 

 to conceive that one large fr'agment was by explosion and imequal heating broken 

 up into many smaller ones. Moreover, were indi\-idual fireballs to contain within 

 themselves numerous small stones, woidd it not rather militate against M. Haid- 

 inger's theory, since the opposing air would then pass between them like a sieve, 

 and the whole notion of the head of the meteorite forcing up before it the film of air 

 that is to curl up behind (to contain the vacumn which on the collapse of the fire- 

 ball is to cause the noise), would have to he abandoned as untenable. 



M. Haidinger's idea that the noise or report is caused by the collapse of the 

 vacuiun can'ied forward in the rear of the fireball deserves attentive consideration, 

 and much might be said in favom* of it as well as against it. Besides the possibility 

 of the noise being due to the discharge of electricity. Dr. Smith likewise considers 

 the noise is not caused by the bm\sting of a solid, but rather by concussion in the 

 atmosphere arising from the rapid motion of the body through it*. Mr. Benjamin 



* But, then, why should we not hear the noise produced by the simple passage of any 



