ought to be slender and long, and filled
with the aforesaid powder well rammed.

"The sheath for making thunder ought to be short and large, and half
filled with the aforesaid powder, and well bound in every direction with
an iron band.

"Note. That in every sheath a small aperture is to be made, in order
that it may be ignited by the match when applied, which match is made
slender at the extremities, but in the middle large and filled with the
aforesaid powder."

Another receipt of Marcus for Greek fire is as follows:--

"Greek fire is made in the following manner. Take pure sulphur, tartar,
sarcocole, (a kind of resin,) pitch, fused saltpetre, and oil of
petroleum. Boil them well together. Dip tow in the mixture, and set fire
to it. This fire cannot be extinguished but with vinegar or sand."

The close analogy, or rather the identity, of these compositions with
gunpowder as at present made, requires no comment. The more important
question is the date at which this work was written. This is a matter of
great doubt. Messrs Reinaud and Fave, from the fact that the receipt for
the preparation of saltpetre to be found in this same book of Marcus is
much more imperfect than that in the Arabian MSS., place the date of his
book earlier than the thirteenth century. Again, Geber, an oriental
writer, the date of whose life is doubtful, but whom our authors fix at
the eighth century, has described the preparation of a salt which has
been translated _nitre_, but which our authors consider to have been a
sesqui-carbonate of soda, _natron_, not _nitrum_. They thence conclude
that nitre was unknown to Geber, and thus, because it was known to
Marcus, that he lived subsequently; and for this reason they place
Marcus between the ninth and twelfth century.

We have seldom seen an instance of more loose deduction than this. It is
required to find the date of Marcus. Geber, whose date is unknown, is
set down, upon rather weak data, as of the eighth century. Geber's
translator is corrected to prove that Geber did not know saltpetre.
Hassan Alrammah, an Arabian, is considered as more recent than Marcus, a
Greek, because his process for saltpetre is somewhat more perfect; and
from the cumulative effect of these data, each of which is very
insufficiently established, and which, if established, only go to prove
differences in the degrees of perfection of their respective receipts,
the date of Marcus is fixed: this certainly is pushing _i