68 PERCY J. EDMUNDI 



magnification is required without sacrificing binocular perspective. 

 In fact for many purposes the retention of perspective is of more 

 import xnce than meie magnification 



(2) For lemohinq the ohjnt fn a rpentn apparent distance This 

 is ettected b) cikuliting the lenticuHi piistii-5 to move tlie object 

 from the nor m il dist mce of 1 nu lies to i qi eafpr dist inc o Here, 

 although the object is re illy luiffnified as well, tlie mignifi(atiou 



greater distance ]ust coiiipensites foi the evtr i appiieiit si/e 

 Theie ire i \erv luge luunbet of pei ons — hud stiidt iit-^ and 

 others -%\hose e>es ^i t ANeikened l)v too toiitum uis ,p|,l„ ition 

 towoik It whit (toi t(nii)Oiuj puqx.M^) nu^lit U . .n^ddMli 



stiuctui d defect, uid hence OTdi!iu\ sp( . t u l! " d . in )r* hum 

 than good The muscles of the txe MinpK 41 1 exhui-tul b\ con 

 tinuous contrictioM uid no doubt the letnn dso b. . ome. less 

 sensitne I cannot help thinkm- that w. ik sp<(ticle. of the 



often caused b\ too con 

 bpectacle-5 would ass>ibt 1 



Tiie onl\ objections \\hich I ha\e heird ad\anced against 

 use of such specticlct, seem to be easd\ answered In the 

 place, I h ive heaid it st ited thit notmal sighted persons could 

 n itui illy rt quae spp( t u h s, and th it to use them must of nece - 

 injure the e\( sight Now this objection, ilthouirh at hist s 

 pLiusible, breiks down completely ^\hell carefully exami 

 Being ess< nti lUv an optical instrument, tht^ cannot, if consti u( 

 properly according to the foimulse gi\( n, produce an\ othei ei 

 upon the eyesight than would result from the use ot a binOL 

 micioscope — w hich experience has slunv n does notiesultin ill eti 



spectadcs would efiectudU 



The argument that th( 

 perhaps ha\e some weight 

 long known and used in con 

 the cure of excessno lont; si 

 however the prisms hi\e lie 

 prevent the "squint that 



