zinc. The images obtained, which are permanent, and which are very much
like those of the Daguerreotype, are fixed by means of the turpentine
and petroleum spirit. They are washed with water, and then carefully
dried. It is possible to obtain prints with half-tones in fatty ink by
means of plates of zinc coated with marine-glue. Some attempts in this
direction were shown to me, which promised very well in this respect. We
are, therefore, in the right road, not only for economically producing
permanent prints on paper, but also for making zinc plates in which the
phototype film of bichromatized gelatine is replaced by a solution of
marine-glue and benzine. The substance known in commerce under the name
of pitch or coal-tar will produce the same results.

_Bitumen Plates_.--A new method of making bitumen plates by contact has
also been introduced into the topographical studios. The plan, or the
original drawing, is placed against a glass plate, coated with a mixture
of bitumen and of marine-glue dissolved in benzine. The marine-glue
gives the bitumen greater pliancy, and prevents it from scaling off when
rubbed, particularly when the plate is retouched with a dry point.
These bitumen plates are so thoroughly opaque to the penetration of the
actinic rays, that the printing-frame may be left for any time in full
sunlight without any fear of fog being produced on the zinc plate from
which the prints are to be taken.

_Method for Topographic Engraving by Commandant de la Noe_.--Before
leaving the interesting studios of which I have been speaking, I ought
to mention a very ingenious application which has been made of a process
called _topogravure_, invented by Commandant de la Noe, who is the
director of this important department. A plate of polished zinc is
coated with bitumen in the usual way, and then exposed directly to the
light under an original drawing, or even under a printed plan. So soon