ncertum per
incertius_ very far. We fear that if no more accurate information be
brought to bear on it, the epoch of Marcus Graecus will be a subject of
as much controversy as ever.

The paragraph in the treatises _De Mirabilibus_ of Albert the Great is
so identical with that of Marcus Graecus, that there can be no doubt of
its being copied from it, or derived from the same source, and is a
strong additional instance of the general progress of inventions. A
received publication calls attention to a fact already disclosed but
forgotten, the knowledge acquired by the world since is brought to bear
on the old fact; and a consequent improvement results.

Roger Bacon, to whom the invention or knowledge of gunpowder has been
attributed by some, would stand a very poor chance among the men of
science of the present day: it is not now the man who conjectures a
possibility, but he who demonstrates a fact, that is hailed as the
discoverer.

The following series of possibilities are curiously interesting, both
from their partial subsequent realization, and from the simple credulity
with which Bacon gives us that which he had known "a wise man explicitly
excogitate."

"Instruments of navigation can be made, men being the propelling agents,
that the largest river and sea barks can be borne along (one man only
managing them) with greater speed than if they were full of navigators.
Carriages can also be constructed which may be moved without animals,
with an inestimable impetus; so that one would think that they were the
armed chariots with which they fought in ancient times. Instruments for
flying can also be made, so that a man sitting in the centre of the
machine, and turning an engine, by which artificial wings may strike the
air in the manner of a bird flying. An instrument also can be made,
small in magnitude, for elevating and lowering almost infinite weights,
than which nothing is more useful in mischances, for by an instrument of
the length of three fingers, and of the same breadth or less, a man may
extract himself and companions from all danger of prison, and elevate
and lower them. An instrument can also be made by which one man may
draw to himself a thousand men, by force and against their will.
Instruments for walking on the sea can also be made, and in rivers to
the bottom without corporal peril. For Alexander the Great used them
that he might see the secrets of the sea, according to the relation of
Ethicus the ast