1802.) 
Mr. W. can have no place in the prac- 
tice of arch-building, becaufe that here 
the arch- ftones cannot aét as true mathema- 
tical wedges. For inthefe, itis well known 
that they are retained in their plates, 
or have their weight, and other force act- 
ing on their back,’ balanced by two 
forces a€ting perpendicularly againft their 
fides, which are conceived to be perfeétly 
fimooth or polifhed. But will Mr. W. 
fay that this is the cafe with the 
voufloirs or wedges of a ftone arch ? 
* Are their fides polithed, or quite void of 
all frigtion ? On tite contrary, does not 
every builder know that their, butting 
fides are fo rough, as by their friction on 
one fide only, in many cafes, to be pre- 
vented from defcending down inthe dix 
rection of the joint? For who is there 
that knows not that a flat-ftone can be 
laid on a furface confiderably raifed or 
inclined to the horizon, as an inclined 
plane, without fliding down, being re- 
tained in that fituation by the roughnefs 
of the furfaces, without any other wedge 
or force above it to retain it, in the man- 
ner of the mathematical wedge. Is it not 
with juftice then, that fuch a theory of 
arches has been long fince exploded, and 
another, more confonant to the principles 
of matter, fubftituted in is ftead ? 
After all, Mr. W. in the rapid 
flow of his declamation, infinuates, in 
Dr. Hutton’s theory, the want of experi- 
mental proofs and mathematical demon- 
ftrations. But furely no candid reader 
can complain that the theory,is not fuffici- 
ently demonftrated in his book. And as 
to experimental proofs, Mr. W. might 
have known, that thefe have not been 
wanting ; practical experiments having 
been made on that theory with complete 
fuccefs. 
Royal Miktary | CHARLES Hurtron. 
Academy, Waokwich, 
Fuly 24) 1802. 
. aa 
To the Editor of the Monthly Magazine. 
SIR, 
MONG your Literary and Philofo- 
phic Varieties for lait month, you 
mention that Mr. Fulton, an American, 
pretends lately to have difcovered a me- 
thod of navigating veflels at any depth 
under water, and of enabling the perfons 
who navigate them to continue immerfed 
for feven hours without the accefs of freth 
air; this invention he intends to apply, it 
is ferioufly afferted, to the purpofes of 
warfare, and, from his ability to approach 
veflels unfcen in a flate of fecurity, he 
propoles to blow men of war to atems, It 
On Subagucous. Navigation. 
St 
is added, the experiment has not been at~ 
tempted in this country, but, the inven- 
tion itfelf was made the fubje& of a very 
formal notice to the Houfe of Peers, with- 
out, however, producing a very grave ef. 
fect upon thatailembly. Whatever might 
be the motive operating on the majority 
ef the individuals compofing that houfe, 
to regard with indifference the commu. 
nication of Lord Stanhope relative to this 
fubject, I am certain that, to thofe who 
are acquainted with the principles of hy- 
droftatics, and the various improvements 
that have been, from time to time, made 
-on the inftruments employed for the pur- 
pofes of diving, the notice of that pro- 
found philofopher will appear in a very 
different point of view... 
Tt feems uncertain, at what period the 
diving-bell was firft invented. Mr. Boyle 
relates, on the authority of others, that 
Cornelius Drebell, during the reign of 
James the Firft, contrived not only a vef- 
fel to be rowed under water, but alfe a 
fluid to be carried in that veffel, which 
could fupply the want of freth air, and 
that a {ub-marine voyage was actually. 
made in it by feveral perfons in the river 
Thames. But, whatever degree of cre- 
dit may be given to the evidence refpect- 
ing this fact, it is, however, certain, thet 
the diving-bell has been long known, ai- 
though it unqueltionably remained in a 
very-imperfect ftate, until improved by 
the celebrated Dr. Halley. The princi; 
pal deteét of the eriginal diving-bell was, 
that it contained but four or five hogf- 
heads of air, which, before it could de= - 
fcend to a great depth, would be com- 
prefled into one, by the weight of the fu- 
per-incumbent water. Now, as, from 
repeated experiments, one man .is found 
to require about a gallon of frefh airte 
fupport refpiration every minute, and as, 
befides, in this inftrument, candles were 
neceflarily employed, which alfo very 
much, tend to confume or vitiate the air, 
it evidently follows that two or. three 
men, with a couple of candles, could not 
remain in it with fafety for a. fufficient 
Jength of time to perform any ufeful la- 
bour. To obviate thefe defects, Dr, 
Halley fixed in the top of his bell a piece 
of ftrong clear glafs to convey light, from 
above, anda cock to allow the efcape of 
the vitiated air, ‘The divers were fup. 
plied with frefh air by means of two. bar- 
rels which alternately rofe and fell like 
two buckets, and as the cold air from the 
barrel flowed into the bell, it expelled the 
hot foul air through the cock. at the top 
of the machine; by which means fuch a 
plentiful 
