'timber; o f diìféfent fhàpbs a&d dimefifiOris, anited to-
'gtefhbh àhd th'éir aètìòn àpbri òfté aiibthet («), may giva
àneiv pòfltioìi fé all Ili e! cónftittìbttt parts, asd a certain
flexibility -or inflexibility, which fbtéf have att effeft on
thè fwiftnefsi òr flbwnefs ò f its itiòtiòn, through the water
; àtìd whàt Is ftill wòrfé, ftraiii particular parts, in
fiith à degree, as tò inakè a fhip Very leàky. It perhaps
ihày bé òbjeéted, thart thè fé obfervaticms are only
ò f hioifaéiil ih the fièrthetn, and moift diftriéts, and that
thòy affe o f nò fighifieàtioh with refpebi tò the warm and
dry air bf the foulhcrh provinces o f Spain ; but I beg
leave td aflert, that they will hold good ih every cli-
ftiàtè, With more of lefs effect, and are o f courfe wot1-
thy bf the notice bf the public at larges as well as thofe
individuals whom thfey may more particularly concern.
p) h i e rate lfariiM «jatólh Bern George Jvran-, publifhed a Vety elaborate and.
feieniific treatife on thisfubjefl, ¡milled, “ Examen maritirna teorico, Pratico, o fra tado ie
Metanica aplicada a la conftraccion, eònoclèmiéntb y ’Miflèjcr tfe 16S NaVrds.^c.” "--
L E T T E R
L E T T E R XX.
Defcriptjon p f the iron mine, and forges, a t Somerrpjlro, in Bifcay.
THE famous iron mine at Somorroftro, in Bifcay,
has Sll the appearance o f being alluvial, .and originally
.compofed.by the congelation o f fotne fluid matter,
increafing by infenfible degrees, and reduced into
.a lamellated flate, fucceffively forming plates, or fcales,
one over the other, thinner than paper; as is evident
•from the many concavities and crevice,s, covered over by
thefe plates; which fuppofing to be the cafe, .we need
not he furprized, at .what has been advanced by fome of
the workmen, who .affine us., that they have of ten founp
broken pieces of pickaxes, mattocks, and other inftru-
• meins, in places that had been worked centuries ago, and
are now replete .with new ore ; if this is ,a fail, -we may
further believe them, .when they aflert, that the mine
increafes, though the flow progrefs o f nature, in this
operation, .does, not permit us to calculate its gradation,
or determine the number o f ages fuflicient, to fill up a
.cavity of any given fize.
A a g .From