Page. Line. 

 Essay. Volume. 



50 116 \9, for {,c,fi',y') read {»',^,y')' 



51 117 12, /or these, re«d those. 



dct J da, 



52 118 2, for -^ read ^=. 



6 from bottom, after the comma add &c. 



53 119 12, for from the mirror, read from the perpendicular surface at the mirror. 



19, forgiven, read given my. 

 54, 120 18, for (a, /3, Y), read (*, /3, Y). , 



O'Y _, d^Y 

 55 121 formula (O"), /or -^,»'£«rf-;^r- 



d' V jdT'V 



51 123 4, for-^'^-^'^'^-a^- 



6{rombottom, for [xz), read (i/z)- 



KR 124 3, for B, R", read R', R". 



7, after parenthesis, add or when the focus is a point of sphenc curvature on 



its own caustic surface. 



19, for /S" read /3/. 



126 15, for negtive, read negative. 



60 



76 



77 



?3 7/" ti y 



127 U, for --ry ■ db\ read -j^. db\ 



61 127 14, jor -^ • au , ,cuu. ^^^3 



62 128 6 from bottom, /or contract, rea^ contact. ^ 



65 131 informula(M"'),/or(,"-F".)(c"-F",), ««<i U" - F%) («" " ^ ^)- 



2 from bottom, /or curvature, read curvatures. 

 67 133 15> Jor surface, read plane. 

 70 136 2, /or CV", rW (V"). 

 73 139 9 from bottom, /or// r.c?T;, rert(f//"r.rfr.ci«. 

 75 14,1 in (I""), /or QW, reaf/QW. 



U2 2 from bottom, /or £ = 2g^ C-i, refl^e = 2c »^C 1. 



U3 6 from bottom, for the negative end, read what may be called the negative 

 end. 

 91 157 in(E(6)),/or[0]-C'--), rearf[0]-("'-^'- ^^ , ^_^^, „ 

 93 159 in(0(«)),/or[T-T']«---'+i-", »-««<^L^-^] - +-. 



da da da db 



103 169 1. >— ^-^'''^«^-■^•■^• 

 in (LC)). /or £y - Cxf, read {By — Cxf, 



