402 JOURNAL OF SCIENCE. 
speculations have been built upon it. Thus, Mr. O. Fisher 
attempts to prove that the ocean basin represents the scar 
whence the mass forming the moon separated from the earth. 
Another cause of gradual retardation in the rotation of our 
planet, and to which, as far as I am aware, very little attention 
has hitherto been paid, is the increase of the bulk of our planet 
by meteorites and cosmic dust. 
There is not the least doubt in my mind that matter, even in 
the most diffused state, cannot leave the outermost or gaseous 
portion of our planet, but that an enormous amount of matter 
in the form of meteorites must have been accumulated year by 
year. Ifwe add to this the cosmic dust falling upon the surface 
of the earth, which, according to a calculation by Nordenskjold, 
may amount to half-a-million tons yearly, the size of our planet 
must have been gaining in dimensions and weight to an almost 
inconceivable degree, even since a rich and diversified flora and 
fauna inhabited it. But even assuming that Nordenskjold’s 
estimate is far too high, and reducing it to a tenth, or to 50,000 
tons yearly, the result of any calculation upon this basis is most 
astounding. Thus if we take only a period of twenty millions 
of years, a short interval in the life history of our planet, the 
cosmic dust falling during that time would add not less than 
1,000,000,000,000 or one billion of tons. 
And this result is obtained without accounting in any way 
for the further addition by the fall of meteorites, without doubt 
of very considerable magnitude. Such a factor, as Professor von 
Nordenskjold forcibly points out in his last work, ought cer- 
tainly not to be overlooked if we wish to account for various 
changes in the form, position, and rate of rotation of our planet 
since it began to consolidate. 
I am well aware that several scientific men, who have care- 
fully examined some of the cosmic dust, have come to the 
conclusion that it is in most cases of terrestrial origin ; but the 
fact remains that some of the dust collected shows its cosmic 
origin by its constituent parts, and that all the meteorites reach 
us from far beyond the atmosphere of our earth. 
The importance of the great doctrine of Evolution as first 
fully established by Darwin cannot be over estimated by the 
paleontologist. Applying the leading facts of the origin and 
distribution of animal and vegetable life, as at present existing, 
to the numberless past generations preserved in the marvellous 
stone-book of Nature, he is able to unravel more fully their 
history, to account for the missing leaves, and to estimate at their 
just value those few remaining, and of which he now and then is 
privileged to decipher a small portion. Darwin himself, in his 
classical chapter ‘“ On the imperfection of the geological record,’ 
in his Origin of Species, has pointed out to us in his usual 
masterly manner how to avail ourselves of the scant material at 
our command, and how future discoveries, adding to the palaon- — 
tological stock, will open out new vistas in the past history of — 
our globe. | 
