Account of the Erection of the Bell Roch Lighthouse. 37 
ings ; but, in the upper or habitable parts of the the Bell Rock 
Lighthouse, a new mode of attachment has been adopted. 
Thk we have already alluded to ; but shall here more fully ex- 
plain. In the outward walls, as will be seen from the section 
given by us in Plate I., the courses of the void are all indented 
perpendicularly into each other by belts, or zones, as Mr Ste- 
venson terms them. This mode of binding the work, consists in 
previously forming a belt or member upon the upper bed of 
each stone, which belt is received into a corresponding groove 
cut into the under bed of the stone to be next laid. In the 
Edystone, the end-joints of the stones of the void are secured 
by detached joggle-pieces, which are slipped into them ; instead 
of which, the end-joggles at the Bell Rock are cut into dovetails 
upon the stones themselves, excepting at the floors, where sepa- 
rate dovetail pieces are employed. — The principles upon which 
the floors of the two buildings are constructed, are essentially 
different. At the Edystone the floors form so many domes, the 
arch-stones of which are built in concentric rings in the usual 
manner, and have a tendency or pressure outwards upon the 
walls. To counteract this pressure two strong iron chains are 
imbedded in the courses, immediately below and above the 
floors. At the Bell Rock, the floors are so constructed, that 
the pressure upon the outward walls is perpendicular; and 
they .*i'e so connected as respectively to form girths or bind- 
ing-frames to the building at each storey. The floor-stones are 
like those of the Edystone, in so far as they are dovetailed into 
the centre stone, but they are of a sufficient length to form at the 
same time part of the floor and outward walls. As a further secu- 
rity, they are otherwise joggled edge-ways, and may thus be 
conceived to form an entire stone, as will be partly understood 
from Plate I.— In all the minor details, the Bell Rock 
works have of course benefited by the more recent improv« 
ments of the Lighthouse Department. The construction of 
the light-room itself, the reflecting-apparatus, and alarm-bells 
for sounding in foggy weather, are all the most perfect of their 
kind. We learn also from Mr Stevenson, who has lately offi- 
cially visited the Tour de Corduan, at the entrance of the Ga- 
ronne, that M. Fresnel, one of the engineers connected with the 
department of Qhausskes et Fonts, under which the lighthouses 
