164 MACHINE ror MEASURING a 
foulnefs it may contract; which would greatly increafe its . 
operation on the index H, and thereby render the gradu- 
ated arch, falfe and uncertain. 
Further, the {pring L may be expofed too much.to in- 
jury from the falt water, if fixed on the outfide of the 
fhip’s bow. ‘To remedy this it may be brought under cover 
by conftru€ting the machine as reprefented by figure 4. 
Where, A B is the rod, C the fulcrum or centre of its mo- 
tion; D the palate; E the horizontal arm leading through 
a {mall hole into the forecaftle: M is a ftrong chain, faft- 
ened at one end to the arm E and at the other toa rim or 
barrel on the wheel G, which by means of its teeth gives 
motion to the femicircle I and index H. The {pring L is 
fpiral and enclofed in a box or barrel, like the main {pring 
of a watch: A fmall chain is fixed to and pafling round 
the barrel is faftened by the other end to the fuzee W. 
This fuzee is connected by its teeth with the wheel G, and 
counteracts the motion of the palate D. NWN are the two 
fockets through which the rod A B paffes, and in which it 
is turned round by means of the little index R.  S is the 
{mall compafs plate, moveable on the top of the upper 
focket N. The plate S hath an upright rim round its edge 
cut into teeth or notches; fo that when the index R is a 
little raifed up, in order to bring it round to any intended 
point, it may fall into one of thefe notches and be detained 
there: Otherwife the preffure of the water will force the 
palate D from its oblique pofition, and turn the rod and 
index round to the direction in which the fhip fhall be 
then failing. Should it be apprehended that the palate D, 
being placed fo far forward, may affe& the fhip’s fleerage 
or obftruct her failing, it fhould be confidered that a very 
{mall plate will be fufiicient to work the machine. I fhould 
fuppofe that one of three or four inches in diameter would 
fully anfwer the purpofe: And yet not be large enough to 
have any fenfible operation on the helm or fhip’s way. 
The 
