its lower flange, so as to prevent the beton from flowing into the
small shaft.

After the shaft was pumped out, digging by hand was begun with a
diameter of 12 feet. After descending 20 inches an 8×10 inch curb was
laid, in order to consolidate the earth and prevent any movement of
the tubbing. Then the excavating was continued to a depth of 31½
inches, and with a diameter of 9¾ feet. At this point another curb was
put in for consolidating the earth. Finally, the bottom was widened
out as shown in Fig. 7, so that three basal wedged curbs could be put
in. This done, the false tubbing was put in place; and finally, when
proceeding upward, the last ring composed of twelve pieces was
reached, the earth was excavated and at once replaced with a collar
composed of twelve pieces of oak tightened up by oak wedges. Each of
these pieces was cemented separately and in measure as they were
assembled.

Through motive of economy no masonry was placed under the base of the
three wedged curbs. In fact, by replacing this with a wedged curb of
wood traversed by six bolts designed to fix the cast iron curb
immediately above, Mr. Chavatte obtained a third curb that he would
have had to have made of cast iron.

* * * * *




ON THE ELEMENTARY PRINCIPLES OF THE GAS-ENGINE.[1]