76 REPORT—1845. 55 : 
and C. gracilis, Utricularia vulgaris, Nymphea alba, Potamogeton: (various) species); 
Sagittaria sagittifolia, and Alisma ranunculoides. The Chara and. Utricularia espe- 
cially seem well-adapted for causing a rapid accumulation of vegetable remains by the 
constant decaying of their stems at bottom, while their upper extremities continue to 
make fresh shoots. After, however, the accumulation has proceeded to a certain ex- 
tent, the pits are so far lessened in depth that at the present day the water no longer 
stagnates there in summer. A different kind of vegetation in consequence then takes 
place. The above plants make way for various species of Junci, Carices, and other 
grasses, which tend rapidly to fill the pits up, but which, growing above the level to 
which the fen is now saturated with water, are not subjected to the conditions under 
which alone the formation of turf is possible. 
On Fizeau’s Process of Etching Daguerréotype Plates, and its Application to 
Objects of Natural History, By A. Goapsy. 
In a Daguerréotype portrait, the black parts of the plate consist of silver, the white 
of mercury, and the intermediate tint of a mixture of the two, the degree of darkness 
or light depending upon the excess either of the silver or of the mercury. In con- 
verting a Daguerréotype into an engraved plate, it is necessary to etch away the dark 
parts and to leave the white untouched. This is done by immersing the plate in.a 
fluid, consisting of dilute nitric acid, nitrous acid, chloride of sodium, and nitrate of 
potash. The nitric acid is so far diluted, that no decomposition can take place until 
the mixture is heated, when the chloride of sodium and nitrate of potash are decom- 
posed, and chlorine and nitrous acid are evolved. These attack and remove the silver 
of the dark portions of the plate, but have no effect on the mercury, so that the lights 
or the picture, being the mercurialized portions of the plate, constitute the etching 
ground, and effectually defend such portions. of the Daguerréotype from the influence 
of the corroding fluid. After a time, those portions of the plate that have been acted 
upon by the chlorine, &c. become covered with a protecting coat of the chloride of 
silver: this must be removed by dilute liquid ammonia, when the biting may be con- 
tinued by a fresh supply of the mixed acid. Grease and foreign matter must be 
removed by repeated washings in dilute acid and alkali, and by boiling in caustic 
potash. These cleansing operations must be repeated after every biting, after washing 
out the chloride of silver by the ammonia. The plate being thus bitten, but in a 
slight degree, is to be inked after the ordinary manner of engravers, and allowed to 
dry ; the surface of the plate is then to be thoroughly polished, the ink still remaining 
in the corroded portions of the plate. It is now to be gilded by the electrotype, those 
parts alone receiving the gold that have been previously polished. The ink is then 
to be dissolved out of the hollows by potash: the parts that are gilded now constitute 
the etching-ground, instead of the mercury, and the biting may be henceforth con- 
tinued by nitric acid, in the customary usage of engravers. The plate thus etched 
generally requires to be finished by the hand of the engraver, who has the advantage 
of a perfect, although faint picture to work upon. The amount of labour which he 
must bestow will depend upon the goodness of the Daguerréotype and the success of 
the etching. M. Claudet has fully established the successful application of this pro- 
cess to the purposes of illustrating natural history, by copying from nature and en- 
graving several delicate and difficult dissections of the lower animals, particularly the 
nervous system of Aplysia and Tritonia (the latter much magnified), and the nutri- 
mental organs in situ of a caterpillar. [These preparations, together with the en- 
gravings of them, were submitted to the examination of the members. ] 
On an Apparatus for Measuring and Registering two dimensions of the Human 
Frame, the Height of the Body and the Space from the extremity of the 
Fingers of one Hand, to the extremity of the Fingers of the other, the arms 
being extended horizontally. By JoszruH Bonomi. 
The adoption of the measurements proposed, the author contends, will furnish a 
more accurate means of identification than the method now in use, and at the same 
time give important data for ethnological inquiry. The apparatus consists of two 
