110 On Meteorites. 
period of most of the comets, the return of which have been ob- 
served, is five or six years. The study of the dates of the different 
falls, therefore, not only suggests that at least a part of the meteor- 
ites move in orbits round the sun, but also intimates a certain rela- 
tion of some of them with a definite group of celestial bodies—viz. : 
the comets of short periods. We have thus established a new link 
connecting the meteorites with the comets in addition to those 
already known—viz.: the strong resemblance of the fire-balls to 
the shooting-stars, as well as the great velocity of several of the 
former, making it probable that they move in orbits of the same 
lengthened form as the comets. If called upon to define the nature 
of a meteorite, briefly and somewhat boldly, I should say, with Mr. 
Newton, the American: A meteorite is a bit of a comet. 
Let me add a few remarks in regard to the question whether there 
is anything in the structure of the meteorites which goes to confirm 
the views here set forth. The orbits of the meteorites being similar 
to those of the comets, the consequence would be, as mentioned 
above, that during a comparatively short time, once in each period, 
when near the sun, they would be exposed to an enormous heat, 
succeeded by quite as enormous a cooling off in the cold parts of 
space. The fragmentary (chondrite) structure, so general in the 
stony meteorites, is perhaps to be explained in this way. On the 
earth the annual and daily heating and cooling produces, as we all 
well know, the weathering or general crumbling of the earth’s crust, 
the formation of stones, gravel, sand and dust. There is a difference 
in regard to the meteorites, in so far as they are not covered with 
water or surrounded by an atmosphere, by which agencies the 
weathering of our earth is brought about; but, on the other. hand, 
the difference between the heat and the cold, owing to this very 
want, and especially to the form of the orbit, must be enormously 
greater on the meteorites ; for while the differences of temperature 
on the earth rarely rise to 50° C., the changes which take place on 
the meteorites must be estimated at 1,000° C., or more. It may 
not, then, be unreasonably supposed that the fragmentary struc- 
ture so common in the stony meteorites is due to the changes of 
temperature they have undergone. How the fragments may have 
become rounded off by being ground against each other or m 
some other way, may easily be conceived, as there are plenty of 
instances in regard to comets, in which movements in their mass 
have been observed. Theoretically, the study of the Tysnæs mete- 
