[ 7 + ] - 
The demonftratlon of all. this is fo well known to 
every geometrician, that it needs not to be inferred ; 
but it may not perhaps be amifs to exemplify what I 
mean, by applying to it a particular cafe. 
The prefent inconvenient and indeed dangerous 
htuation of the two lights at the mouth of the 
Humber, commonly called the Spurn Lights, mull 
probably foon make it necelTary to remove them ; 
for the ground, upon which they formerly flood, is 
now fo far wafhed away, as not to leave fuflicient 
room to eredl them at a proper diflance from each 
other ; and frefh ground being grown up to the 
fouthward, fo as to make the point above a mile di- 
jflant from them, fliips are frequently thereby liable 
to be deceived. Jn cafe therefore thefe lights fliould, 
at any time hereafter, be removed nearer to the point, 
I think the foregoing principle might be very con- 
veniently and advantageoufly applied, fo as to enable 
entire flrangers to enter the Humber, with the greatefl 
where the fegment, correfponcHng to 120", iiiterfefts the liixe 
DE, will be the centre of the fegment correfponding to 60°: 
the point, where the fegment correfponding to 80°, interfedfs 
the line D E, will be the centre of the fegment correfponding 
to 40°, &c. 
There is another method of finding the centres of thefe feg- 
ments, which, if great cxadlnefs is required, will perhaps be 
found preferable, in practice, to the former, efpecially in the 
larger fegments. The method, I mean, is to fet them off by a 
fcale, in which cafe the diftance of the feveral centres, from the 
point A, muft be refpc(ffively proportional to the co-tangents of 
the angles in their correfponding fegments, or, what is the lame 
thing, refpedlively proportional to the tangents of the angles 
D C A, F C A, GCA, H C A, ^^c. confiituted upon the line 
AC, at the point C; for, making A C the radiu-, the lines 
D A, F A, G A, H A, &c. arc the rcfpe<Stivc tangents of thofc 
feveral angles, 
fecurity, 
