alone. One, in West Virginia, is 70 feet high, and 1,000 feet in circumference. They are truncated, and their summits are supposed to have been occupied by edifices—probably temples which have disappeared. Lines of artificial embankments remain which enclose from 100 to 400 acres, and evince a considerable degree of geometrical knowledge in their plans. Many articles, as vases, pottery, fragments of cloth, and copper implements, have been found in them, indicating considerable industrial skill. There is evidence that, since they were built, the rivers have changed their courses, and it is also a significant fact regarding their antiquity that the human skeletons found within them are in a state of decay so advanced that they crumble to pieces as soon as touched. Skeletons found elsewhere, and known to be 2,000 years old, are still compact, and comparatively well preserved. An interesting fact in regard to these aborigines is, that they knew something of mining. In the copper-mines of Lake Superior, old excavations for the extraction of the metal, 30 feet deep, have been discovered. Mining implements were found in the cavern, and trees 400 or 500 years old (as ascertained by counting their annual rings) stood upon the débris. Prof. Newberry, Geologist of the State of Ohio, informs us that he has found evidence of the ancient working of oil-wells and lead-mines.
The indications of civilization in Central America, Mexico, and Peru, are still more perfect. The author states that the great Peruvian roads of stone, lime, and cement, 25 feet wide, and with a strong wall on each side, and carried over rivers, marshes, and mountains, and as long as both our Pacific Railroads, make these boasted works of the nineteenth century dwindle into insignificance.
Mr. Baldwin's book is neatly and copiously illustrated, and it has the excellent defect of being too brief.
PROF. TYNDALL'S NEW BOOK.
The first volume of the "International Scientific Series" will be by Prof. Tyndall, on the "Forms of Water," and will treat of the mutations of this element in the great operations of Nature, especially in the phenomena of glaciers. We publish a short article from the advanced-sheets, which will give an idea of the lucid simplicity of the style in which it is written. Prof. Tyndall throws his statements into the direct colloquial form, as if he were talking to a young student beside him, and showing him the things he is talking about. There is true art here as well as science—the art of forcible, effective, vivid presentation by which words become pictorial to the imagination. Prof. Tyndall is as skilful in his manipulation of language as of his scientific apparatus, and he sets his successors in the International Series an example which it will be not easy for them to imitate.
While speaking of Prof. Tyndall, it may be proper to add that he intends visiting the United States in the autumn, perhaps early in October. He will come to see his friends (and he will find them numerous), and to get acquainted with our people; but it is not his purpose to exploit the country as a lecturer. He may probably give a few lectures, but he will embarrass himself by no previous engagements.
CONCERNING ATOMS.
Dr. S. D. Tillman publishes in the American Chemist an able paper on "Atoms and Molecules," in which he reviews the present state of the question, and gives the reasons why we should still hold by the atom, notwithstanding the attempts made to get rid of it. Both sides of the question were early taken, on purely speculative grounds. The ancient philosophers, in their subtle reasonings on the constitution of Nature, asserted the existence of ultimate indestructible material atoms. Others, and notably Boscovich, at a later day denied the material atoms, and substituted for them what he termed centres of force. Modern chemistry, however, approached the subject from a different point of view. It was proved that the interior changes and reactions of matter are governed by definite mathematical laws, and it was inferred that material substances must therefore be made up of ultimate material units. The assumption was made, because it best explained
