110 VISION WITH THE COMPOUND MICROSCOPE 



dvf 

 i ) X ( ) X + 7 1 



. when i/ = <>... = UlN - j- (?</ 



?t u 



= (.) F. suppose. 



If , = o. or the ray be parallel to the axis before refraction, we 



have t'roiii (< s ) 



/ nd the e( (nation to the refracted ray beconu 



/, __ < t , '- , 



es 



, when = ,,. ., = O N' - | = O N' - - 



/' // 

 = F', suppose. 



^ -,n.l F' are called the ' focal points.' 



t + d ' 



ii d it 



OF/ = ()N " - p (>-<,) -du, 

 The focal distance -/= F - E = O E' - O F' 



_ _ 



yu (/ - ") dull' /.' 



Similarly, it may l- >lio\vn that if there be two lenses, and sub- 

 si-i-ipt numbers ivf.-i- t.> tlu- first and second lens respectively, while 

 E, E', F. F' refer to the entire system, and if 



< =()E, OE/, 



= 



/'2 ' ''l 



~ 



r, + /x, r._, + < 



= OE 1+ Lfe + -* 



//._, (^, + ?<-,) 

 2 i + A'i r -2 + Sf { f 



\\'c are no\\ prepared to /',,,/ <>nl an I'.i-n in/>l<' <>f lit,- f,'(diss sy 

 \<\ tiacini; a ray through two or more leii.scs on all axis, showing how 

 an\ ronpipitc may 1 >e I'ound 1 lirou^h t \vo or more lenses on that axis. 1 



I;, lemberi] ..... m object, aaid thr iissunifd finulitiuns nt -ionic for whom we 

 UTI; nut lii'sit.ili' bo 1'ivf.iri- thi^ with the following imtc-- to ivuiind the 



ed to certain mathematical expressions. 



mi-mi-, iniiint-, \ plane surface of a l<-n^ is considered a spherical surface of 

 an iiitiniti- i-iuliiis. \M' ininilii-r divided l>y d any number divided byO = o^; 



