406 Proceedings of the Royal Physical Society. 



2. The smaller rounded or lobed portion, 



In air, 5 lbs. 10 oz. 2J drs. (Avoir.) 

 In water, 4 „ 11 „ 9J „ „ 

 Specific gravity, . . . 6*1919" 



The difference in the specific gravity of the halves of the 

 meteorite may probably be explained, by the presence, in the 

 smaller portion of the mass, of the principal part of the large 

 furrow already referred to — filled up with earthy-looking 

 matter* of lighter specific gravity. 



In conclusion, I may add a few notes on the general sub- 

 ject of Meteorites or Aerolites. 



Theories of the Source or Origin of Meteorites. — Various 

 theories have been at different times brought forward to ac- 

 count for the presence of meteorites or aerolites, these strange 

 and apparently accidental visitors. 



These theories may be arranged in two great divisions : — 



First, The terrestrial sources — the source or origin of these 

 bodies being supposed to belong to our earth ; and, secondly, 

 The cosmical sources, which derive their origin from beyond 

 our earth. These again may be each subdivided into two 

 sections, or classes, as follows : — 



I. Terrestrial Sources. 



1. Volcanic — from the volcanoes of the earth. 



2. Atmospheric — from their supposed formation in the 

 atmosphere of our earth. 



II. Cosmical Sources. 



1. Lunar Volcanic — from the volcanoes of the moon. 



2. Interplanetary Space — the planetary or asteroidal 

 theory. 



I shall not enter here into the arguments that have been 

 brought forward both for and against these various theories, 

 merely remarking that the old idea of their terrestrial origin is 

 now almost entirely given up. The second of these divisions, 

 and in particular that which derives their origin from a sup- 

 posed belt of planetoids or asteroids revolving in space on the 

 borders, or just beyond the most distant part (from the sun) of 



* Dr Thomson afterwards examined some of this earthy- looking matter, and 

 found it to consist of the same chemical components as the rest of the mass, 

 the iron, however, being in the state of an oxide. 



