book which, on account of the large maffes of ice driven down the
'— .— > ftream from the Lake Ladoga, is ufually removed * when they
firft make their appearance; and for a few days, until the
river is frozen hard enough to bear carriages, there is no
communication between the oppoiite parts of the town.
The depth of the river feems to render it impoffible to
build a ftonebridge; and even if one could be conftrudted,
k mult neceffarily be deftroyed by the vaft ihoals of ice,
which in the beginning of winter are hurried down the rapid
ftream of the Neva. In order to remedy this inconvenience,
a Ruffian peafant has projedted the fublime plan of
throwing a wooden bridge of a fingle arch acrofs the river,
which in its narroweft part is 980 feet in breadth.
The artift has executed a model 98 feet in length, which
I .examined with great attention, as he kindly explained its
proportion and mechanifm.
The bridge is upon the fame principle with that,of Schaff-
haufen, excepting that the mechamim is more complicated,
and that the road is not fo level. I ihall attempt to defcribe
it by fuppofing it finiihed, as that will convey the beft idea
of the plan. The bridge is roofed at the top, and .covered
at the files : it is formed by four frames of timber, two on
each fide, compefed of various beams or truifes, which fup-
• ga*irm, a violent N . W . win'd drives the wa- mouth o f the Balrick.
ters o f the Northern Océan, during the.in- See Notices et Remarques fur les debor-
flux o f the tide, into the Baltick,. and is ac- demens de la Neva à St. Peteribourg accompanied,
or iuftantaneoufly fuceeeded'by compagnies d’ une carte reprefentant la
a S. W . wind in that fea and the G u lf o f criie et 'la diminution des eaux, &c. In
.Finland. A ll thefe circiirtfftances concurred Nov. A c. Pet. for 1777, P. IT. p, 47. to
at the inundation o f 1777 : it happened wjiich excèdent treatiie 1 would refer the
'tw o days’ before the autumnal equinox, four curious reader for further information.
.béforethefüllmoon,twoàfterpairingthrough * When I was at Peteriburgh, the ’bridge
the perigæum, and by a ftorm at S. W . which which had been taken away was -replaced,
•Avas preceded by ftrong W. winds .in the and continued 'during the whole winter.
¿Northern Ocean, and iirong N. winds at the
port
port the whole machine. The road is not, as is ufual, car- chap.
ried over the top of the arch, but is fufpended in the middle.. m' ■
The following proportions I noted down with the greateft
exadtnefs at the time when they were explained to me by
the artift.
Length o f the abutment on the north end ¿^g feet>
Span o f the arch
Length o f the abutment on the fouth end 658
Length o f the whole ftrufture, including the abutments 22cfi
T h e plane o f the road upon its firft afcent makes an angle o f five degrees
with the ordinary furface o f the river '
Mean level o f the river to the top o f the bridge in the center £ 168
Ditto to the bottom o f the bridge in the center 126
Height o f the bridge from the bottom to the top in the centre 4*
Height from the bottom o f the bridge in the center to the road 7
Height from the bottom o f ditto to the water 84
Height froriv the water to the Ipring o f the arch r6
So that there is a difference of 35 feet between the road at
the fpring of the arch, and the road at the center; in other
words, an afcent of 35 feet in half 980, or in the fpace of
490 feet, which is little more than eight-tenths of an inch
to a foot * . The bridge is broadeft towards the fides, and di-
minifhes towards the centre.
In the broadeft part it is 168 feet
In the center or narroweft 42
T h e breadth o f the road is 28
The artift informed me, that to complete the bridge would
require 49,650 iron nails, 12,908 large trees, 5,500 beams
to ftrengthen them, and that it would coft 300,000 roubles,
or .£60,000. He fpeaks of this bold projedt with the ufual
warmth of genius; and is perfectly convinced that it would
be practicable. I muft own that I am of the fame opinion,
* T h e afcent o f the road o f the bridge at Schaffhaufen is barely four-tenths o f an inch
in a foot.
though