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 : — 
Firsts 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. 
