ring. The roof is 64.520 meters wide and 14.628 meters high; and its total
weight is 103.300 kilos. for the ironwork--representing a weight of 31.6
kilos. per square meter of surface. It is proposed to employ for its
covering wooden purlins and tin plates. The whole construction has a light,
pleasing, and yet thoroughly solid appearance.


RAISING THE ROOF.

Herr Brenner, the engineer of the Erdberg Works, gives a description of how
the roof of a house, 54.6 meters wide, for a gasholder in Berlin, was
raised to a height of 22 meters. In that instance the iron structure was
put together at the bottom of the tank, leaving the rafter ends and the
mural ring. The hoisting itself was effected by means of levers--one to
each rafter--connected with the ironwork below by means of iron chains. At
the top there were apertures at distances of about 26 mm. from each other,
and through these the hoisting was proceeded with. With every lift, the
iron structure was raised a distance of 26 mm.

[Illustration: FIG. 2.]

Herr Brenner had considerable hesitation in raising in the same way the
structure at Erdberg, which was much larger and heavier than that in
Berlin. The simultaneous elevation to 48 meters above the level, proposed
to be effected at forty different points, did not appear to him to offer
sufficient security. He therefore proposed to put the roof together on the
ground, and to raise it simultaneously with the building of the wall;
stating that this mode would be perfectly safe, and would not involve any
additional cost. The suggestion was adopted, and it was found to possess,
in addition, the important advantage that the structure could be made to