92 . On hardening and tempering Steel. | 
equal, the velocity with which the hydrogen gaz enters the 
balloon, will not experience the leaft change, When. the 
firft gazometer is entirely empty, the cock Z1_is tut, and 
the firft gazometer is filled; and the. cock-Z1 is nat opened 
till a little before the fecond gazometer is totally. gmptied, 
The fecond gazometer is then.to be filled again, and in. this 
manner the combuftion of hydrogen gaz may be continued 
by thefe gazometers to any length of time without 1 interrup- 
tion. To introduce. the oxygen gaz without interruption 
imto the balloon by means of two gazometers, it will be 
fuficient that the two cocks, which form a communication 
between the gazometers and the balloon, be immediately 
fixed in ‘the covering of the latter. ’ 
Both halyes of the apparatus being fimilar, the letters of 
reference are only marked on that part which is given in 
outline upon the plate. 
EX. On the Choice of Steel, and the' Methods of bardining 
_and tempering it. By Mr. S. Varzer. Communicated by 
the Author. 
Ir feldom happens that theory and practice are united in 
the fame individual: the man of fcience often labours 
under a great difadvantage (notwithftanding his excellent 
theories) for want of the experience of the practitioner, and 
the practical man feldom has.a theory to guide him. He 
knows from experience that certain things or operations will 
produce a particular effect, but can give no. reafon why. 
“His application to bufinefs has not allowed him. time. to 
fearch into caufes, nor to reafon upon effects ; and it would be, y 
difficult to perfuade this ufeful clafs of men how much theo- 
retical knowledge might be gained by applying their lei- 
fure hours to Ae and how much pleafure might be de- 
rived from thus uniting theory with practice, which e mu- 
tually affit each ty 
: 
Twas i 
