636 sir david brewster's description of a 



to the focus F', from which it diverges, and falling upon the lens AB, is refracted 

 by it, and the lens LL into the parallel beam RR, or, if we use only the lens 

 AB, into the parallel beam rr. 



The cone of rays FQR, which radiates from F, is thrown back to F by the 

 part QR of the spherical mirror HQRK, and falling upon the lens PSP, is re- 

 fracted like the direct cone FPS into the parallel beam RR or rr. 



The two cones of rays FKK, FHH, intercepted by the lenses KK, HH, are 

 refracted into parallel beams, which, falling upon the plane reflectors cd, ej\ are 

 reflected into the parallel beams r"r", r'r'. In like manner, the cones of rays 

 FWW, FYY are refracted by the lenses WW, YY into parallel beams, which, 

 falling upon the plane reflectors c'd', e'f, are thrown into the parallel beams 

 PP, pp. 



The cone of rays FRY, falling upon the part RY of the spherical mirror HQRY 

 is returned through the flame F, from which it diverges, and falls as a second cone 

 upon the lens KK, which throws it into a parallel beam, which is reflected into 

 the beam rr by the reflector cd. In like manner the cone of rays FHQ is, by 

 means of the lens WW, and reflector c'd', thrown into the beam pp. 



The eight cones of rays which issue from the flame F, being the whole of its 

 light, thus passes into the wide compound beam r'p, consisting of the principal 

 beam RR, and the four beams r'r 1 , r"r", p'p', p"p". The beams rr and p'p' are 

 each composed of one cone of rays FHH, FRY, and the beams r"r", p'p of two 

 cones of rays, the one direct, and the other reflected. 



If we now place a second flame at F', and surround it with the lenses and 

 reflectors shown in the figure, it will become a second holophote. The cone of 

 rays FAB, refracted by the lenses AB, LL, will add its light to the central beam 

 RR, and the opposite cone F'PS, refracted by the lens PS' to F, from which it 

 falls upon the mirror QR, will be reflected through the flame F', from which it 

 diverges and enters into the beam RR, like the direct cone FAB. 



The cone FCC, refracted by the lens CC, is reflected by the plane mirror ab, 

 so as to form a new beam r'"r", filling up the space between the beam r"r", and 

 the central beam RR. In like manner the cone FDD is made to fill up the space 

 between p'p' and RR, by means of the lens DD and the reflector ab'. 



The cone of rays F'GM, intercepted by the spherical reflector GM, as reflected 

 through the focus F", and by means of the lens DD and the reflector a'b\ is thrown 

 into the beam p'"p' . In like manner the cone of rays F'EN, reflected by the 

 spherical mirror EN to the flame F, will pass into the beam r'"r"\ by the refraction 

 of the lens CC and the reflector ab. 



If it is desirable to have, for any special purpose, a more intense and a wider 

 beam, we have only to substitute a lens in place of the mirror QR, and intro- 

 duce through it the light of one or more holophotes, the cones of rays passing 

 through the lens at QR, adding to the intensity of the central beam RR, the 



