On the Properties of Metal and Wooden Springs. 67 
one float has been raifed ,%, and the other depreffed as much; 
which, inftead of indicating calm weather, denotes that 
tempeftuous weather may be expested. 
_ The weight of the atmofphere at great heights might be 
difcovered, by fufpending this inftrument to an air-balloon. 
Sees 
XII. On the different Properties of Metal and Wooden 
Springs. 
Ti E {pring i is, in a variety of pieces of mechanifm, not 
only a very ufeful auxiliary, but in fome (as in pocket- 
watches, gun-locks, &c.) an indifpenfible requifite. But 
from the difficulty of getting {prings to ftand, as the work- 
men expreéfs it, to their temper, they are not fo frequently 
applied to the purpofes of mechanics as otherwife they might 
be. Great judgment and {fkill, as every one knows who is 
converfant with the fubject, are required to give to a metal 
fpring its due degree of temper; for, if made too hard, it 
{naps ; if not hard enough, it fets. Metal {prings, however, 
frequently fail from another caufe, which is very little under- 
ftood ; in confequence of which, the failure is ufually attri- 
buted, though, as prefently will be feen, unjuttly, to the 
unfkilfulnefs of the workman. It is a circumftance not com-. 
monly obferved refpecting a metal fpring, that if it has not 
fomething to ftop againft, but is fuffered to vibrate after pers 
forming the requifite aGtion, it will, in a fhort {pace of time, 
if the aétion be frequently repeated, either break or fet. 
Whence this property arifes is not at prefent the object of 
enquiry. Itis mentioned that, in cafes which will admit 
of it, this inconveniency may be guarded againft. In thofe 
cafes in which the vibration cannot conveniently be avoided, 
a wooden {pring, which is not fubject to the like inconve- 
niency, is the beft, and, perhaps, the only fubftitute. A 
wooden {pring is, in the property alluded to, the reverfe of a 
metal one :. if flopped in its vibration, it foon fets or breaks ; 
Fa if 
