TRANSACTIONS OF THE SECTIONS. 19 



the contrary, when the meteor considered above is arrested by the atmosphere, 

 then the air rushing in from all sides would fill up the vacuum, till then sur- 

 rounded by the film of incandescent air emanating from the centre of expansion 

 in front of the advancing fireballs. 



I believe I am safe in assuming the following deductions as well explained : — 



1. The incandescent ball is produced by the compression of the atmospheric air. 



2. The sounds, reports, and rimiblings are produced by the concussion of the air 

 in the vacmmi of the fireball when arrested. 



3. Showers of aerolites in the generality of cases are produced by groups of 

 meteorites enteiing oUr atmosphere togethei*. There may oe in some cases larger 

 masses flying to pieces by rotation. 



4. The crust is produced by the melting of the superficial portion of the fi'ag- 

 ments. The high temperature produced is lowered immediately after the begin- 

 ning of the real fall by the intense cold of the interior. 



1 have enumerated these points to show the concordance in some, and the differ- 

 ence of opinion in others, of those enimierated by Prof. Laurence Smith in SiUi- 

 man's American Jom-nal, vol. xxxi. January 1861, p. 98. 



n. Origin of the rocky substance of Aerolites. — Having to account for b, fragment 

 of rock broken otf fi'om its original repository and traversing cosmic space by itself, 

 the question is simply to give, as a first step, an outline of the possible consolidation 

 of matter in its most attenuated condition into a solid body, and then to give a plau- 

 sible cause why it may be shattered to pieces. The theories of the present day, 

 that of La Place at the head of them, are familiar to philosophers. All of them 

 must assume cosmic matter in the finest state of dust to begin with. But the as- 

 simiption of a temperature so high as to contain only one thirteen-millionth part 

 of a gi-ain (0-000013) in a cube of space, the side of which is of the length of one 

 German mile, is far too gratuitous, as well as inconsistent with our knowledge of 

 the physical properties of matter. We know cosmic space to be intensely cold. 

 For thousands of years there has been no change experienced relative to the tem- 

 peratm-e of the earth's sm-face. 



It may be a question whether it may not be possible for heat to be generated 

 even in the cold of cosmic space, by the simple action of gravitation upon the par- 

 ticles of attenuated matter, in thefr most nascent state. This will lead to conse- 

 quences closely agreeing with the views of De la Rive, Sir Charles Lyell and others, 

 as to the production of the central heat of our planet, as quoted by Prof. Naumann 

 in his ti'eatise on Geology, page 63. Now we may aiTange all sorts of meteoric 

 rocks in an imintenoipted series, beginning with the most crystalline state that 

 many meteorites and meteoric irons frequently exhibit, and following them up to 

 several of those marbled composite specimens, such as those of Pamallee, Breme- 

 vorde and others, which bear the closest resemblance to our tufaceous deposits, but 

 in which no water has been at work. I have ventiu-ed to propose for this charac- 

 teristic structm-e the expression of " Meteoritic Tufa." And even beyond that, 

 there are still more tender and fragile specimens, approaching to mere aggregations 

 .of powder or dust, like the one of the fall at Alais, March 15, 1806, or of Cold 

 Bokkeveld of October 13, 1838. It is certainly a fair induction to suppose the more 

 solid and crystalline of these rocks to have been fonued out of the consolidation of 

 matter originally in a state of dust, or nascent. 



If we conceive the diagram, fig. 4 (taken fi-om Dr. Kopp's article, " Physik und 

 Meteorologie," in the Biideker publication on Natural 

 Science, Die gesammten Naturwissenschaften), to repre- 

 sent a large globe of cosmic matter in the state of the 

 finest impalpable dust in its most "nascent state," every 

 point situated like A will be attracted with equal force 

 by other points B and D similarly situated, so that its 

 total direction will tend towards the centre C. Near the 

 centre, the attraction towards it will not be nearly so 



Sowerful ; in the centre itself givwtation will have no 

 efinite direction at all, the particles of matter being 

 solicited by attraction in each of the diverging du'ections. 

 Consolidation then will depend upon the pressure coming 

 into play from the surface stratum only. 



