ASTRONOMY AND METEOROLOGY. 347 



heights may be stated to be, i-espectively, 73 and 52 miles, at first 

 appearance and disappearance above the surface of the eaith, with 

 a probable error of not more than two or three miles. The average 

 velocity of shooting stars in sixty-six instances is 34.4, or, in I'ound 

 numbers, 35 miles per second. Fifty-six general radiant points of 

 shooting stars have now been shown to exist in different seasons of 

 the year, which represent, with a considerable degree of accuracy, 

 the whole of the available observations recorded up to the present 

 time in existing catalogues. These general radiant jioints belong 

 to fifty-six annual star showers, as well determined, in the major- 

 ity of cases, as to limits of their duration and positions of their 

 i-adiant points, as is the case with the older and better-known 

 showers of August and November. The currents, zones, or belts 

 of meteoi's which they indicate, encompassing the sun, are more 

 or less rich and long-enduring. They appear to give rise to occa- 

 sional star-showers l^y pailieular concentrations of their materials 

 — perhaps even to fireballs — by a still closer compacting of their 

 particles. 



M. Liandier has communicated to "LesMondes" the follow- 

 ing conclusions, which embody the result of three years' observa- 

 tion : " The shooting stars which leave no trace of their trajecto- 

 ries travel in the same direction as the dominant air currents of 

 the upper regions of the atmosphere at the time ; those with trains 

 in the opposite direction." 



PHYSICAL HISTORY OF METEORITES. 



The following are extracts from a communication of Mr. H. C. 

 Sorby, F.R.S., to " Silliman's Journal," of January, 1866 : — 



"As shown in my paper in the 'Proceedings of the Royal 

 Society' (xiii. 333), there is good pi'oof of the material of meteor- 

 ites having been to some extent fused, and in the state of minute 

 detached particles. I Iiad also met with facts which seem to show 

 that some portions had condensed from a state of vapor, and ex- 

 pected that it would be requisite to adopt a modified nebular hy- 

 pothesis, but hesitated until I had obtained more satisfactory evi- 

 dence. The character of the constituent particles of meteoi'ites, 

 and their general microscopical structure, differ so much from 

 what is seen in terrestrial volcanic rocks, that it appears to me 

 extremely improbable that they were ever portions of the moon, or 

 of a planet, which differed from a lai-ge meteorite in liaving beeu 

 the seat of a more or less modified volcanic action. A most care- 

 ful study of their microscopical structure leads me to conclude 

 that their constituents were originally at such a high temperature 

 that they were in a state of vapor, like that in which many now 

 occur in the atmosphere of the sun, as proved by the black lines 

 in the solar spectrum. On cooling, this vapor condensed into a 

 sort of cometary cloud, formed of small crystals and minute drops 

 of melted stony matter, which afterwards became more or less 

 devitrified and crystalline. This cloud was in a state of great 

 commotion, and the particles moving with great velocity were 

 often broken by collision. After collecting together to form larger 



