On Water-Pressure Engines for Mines. 309 
and the volatile matter which T obtained, escaped his no- 
tice altogether. If we were to add them to the alumina, it 
would make the two analyses almost the same. No mineral 
has hitherto been found containing nearly so much soda as 
this. Hence the reason of the name by which I have di- 
stinguished it. 
LUI. Afr. Farey’s Reply to Mr. Joun Taytor on Water- 
Pressure Engines for Mines. 
To Mr. Tilloch. 
Sir, I SHOULD probably have passed over the observation, 
at page 394, of your last volume, that though various con- 
structions of avater- pressure engines had been attempted, 
none had vet been very successtully made on a large scale, 
had J not heard the comments thereon by a Cornish mine- 
owner, very conversant with the mines of that county, 
which tended to show, that no pressure engines in Corn- 
wall were at ‘all comparable in mechanic effect, with that 
which he recommended Mr. Trevithick to the erection of 
at Yolgrave,in Derbyshire; and which brought strongly to 
my recollection the opinions to a similar effect, which I 
heard from numbers of the best informed miners in Der- 
byshire, when I was on my survey of that county; and had 
more than once heard the particulars stated of the quantity 
of water lifted, &c.: but having then letters of recom- 
mendation in my pocket, to the principal proprietor of the 
mine where this engine was erected, I purposely neglected, 
and when at the mine also, to note down the paruculars, 
which the agent mentioned from memory, as [ was as- 
sured of seeing the working, drawings, and every particular 
respecting the engine, when I called on the gentleman. al- 
Juded to at some miles distance :. unfortunately <his was 
delayed by circumstances until I was about leaving the di- 
strict, and when I called, the gentlenian was from home: 
-yet sill, as a month had passed over without any one of 
your correspondents baving noticed the above assertion, 
1 thought it but an act of justice to an-enginecr, who is 
looked upon as having performed an essential service to 
the miving interests of Derbyshire, but whom I never saw 
or had any communication with whatever, to state what I 
did, at page 5, of your present volume. As I am unac- 
quainted wifh any rule by which to know how much water 
a shallow mine or adeep one may produce, without kgowing 
s U3 any 
