apparatus. Under such circumstances, Mr. Chavatte considered this
moss-box as more detrimental than useful, and not at all
indispensable, and so substituted beton for it, as had previously been
done by Mr. Bourg, director of the Bois-du-Luc coal mines.

[Illustration: FIGS. 1, 2, 3, 6 AND 4.--Details of dredge. FIGS. 5 6
AND 6.--Details of maneuvering lever. FIG. 7.--Mode of lengthening the
axis of the dredge. FIG. 8.--Hooks for lifting the dredge bags. FIG.
9.--Arrangement of valves in the beton box. FIG. 10.--Device for
centering the tubbing.

PLATE II.]

This engineer likewise suppressed the balancing column, which is often
a source of trouble in the descent of the tubbing, and forced his
tubbing to center itself with the shaft through a guide with four
branches riveted under the false bottom that entered the small shaft
(Pl. 2, Fig. 10). Mr. Bourg so managed that there remained an empty
space of ten inches to fill in with beton. Mr. Chavatte had at first
intended to proceed in the same way, but the two last tubbings, upon
which he had not counted, forced him to reduce the space to 5¾ inches.
Under such circumstances it was not prudent to employ the same means
for guiding the base of the tubbing, because, if the central shaft had
not exactly the same center as the large one, there would have been
danger of throwing the tubbing sideways and causing it to leak. Seeing
which, Mr. Chavatte strengthened the lower part of the base ring and
placed it upon another ring tapering downward, and 27½ inches in
height (Pl. 1, Fig. 5). The object of this lower ring was to force the
tubbing to remain concentric with the shaft, to form a tight joint
with its upper conical portion, and to form a joint upon the seat with