consists of a thin concave of copper, fixed by three wires, at about an
inch above the chimney-glass of the lamp, yet capable of being taken off
at pleasure. The gaseous carbonaceous matter which occasionally escapes
from the top of lamps, is thus arrested beneath the concave cap, and
subsequently consumed by the heat of the flame, instead of passing off
into the room, in the form of smoke or smut on the ceiling and walls.

[The "Technical Repository," may have the credit of introducing this
contrivance to the British public; but it is somewhat curious that it had
not been previously adopted, since scores of lamps thus provided, are to
be seen in the cafés and restaurateurs of Paris. _Apropos_, the French oil
burns equal in brightness to our best gas, and as we are informed, this
purity is obtained by filtration through charcoal.--ED.]


_Caddis Worms._

The transformation of the deserted cases of numberless minute insects into
a constituent part of a solid rock, first formed at the bottom of a lake,
then constituting the sides of deep valleys, and the tabular summits of
lofty hills, is a phenomenon as striking as the vast reefs of coral
constructed by the labours of minute polyps. We remember to have seen such
_caddis-worms_, as they are called by fishermen, very abundant in the
wooden troughs constructed by the late Dr. Sibthorp, for aquatic plants,
in the botanic garden at Oxford, to the cases of which many small shells
of the G. Planorbis Limnea and Cyclas were affixed, precisely in the same
manner as in the fossil tubes of Auvergne; an incrusting spring,
therefore, may, perhaps, be all that is wanting to reproduce, on the banks
of the Isis or the Charwell, a rock similar in structure to that of the
Limagne. Mr. Kirby, in his "Entomology," informs us, that these larvae