xc. 



NEW SOUTH WALES LIGHTHOUSES. 



tan ^ sin " ■ tan^ smcr 



fX COS p — 1 jx COS o- — 1 



r = (b-t tan p) cos p 



2 sin J (»A-^)cos[i(^ + ^)-p] 

 a; = r cos \f/ - 1 ; y = r sin \f/ -f tan j3 - t ban o- 



Prob. 2. 

 Having found the centre of curvature by the preceding 

 formulae, — to determine the path ol any ray. 



// / 



'' 



/>. 



\ 



sin <£ =/x, sin (0 - p) 



/a sin p = sin a 



ix sin p 



tan $ = '- " — 



/x cos p — 1 



Prob. 3. 

 Prism giving two refractions and one reflection. 



Pro^/enf J* 



