<5 C U L A & S f E C T R A, SECT. XL. 20. 



In viewing the fpectra of bright objects, as of a 

 area cff red filk of half an inch diameter on white 

 paper, it is eafy to magnify it to tenfold its fize : for 

 if, when the fpectrum is formed, you (till keep your 

 eye fixed on the filk area, and remove it a few inch- 

 es further from you, a green circle is feen round 

 the redfilk; for the angle now fub tended by the 

 iiik Is Ids than it was when the fpedrurn was form- 

 ed, bt that of the fpeclrum continues the fame, 

 and our imagination places them at the fame -dif- 

 tance Thus when you view a fpectrum on a fheet 

 <jf white paper, if you approach the paper to the 

 eye, you may diminifh it to a point ; and if the pa- 

 per is made to recede from the eye, the pe$rurn 

 will appear magnified in proportion to the diftance. 



I was furprifede and agreeably amufed, with the 

 following experiment. I covered a paper about four 

 inches fquare with yellow, and with a pea filled 

 with a blue colour wrote upon the middle of it the 

 word BANKS ki capitals, a* in Fig. 5, and fitting 

 with my back to the fun, fixed sny eyes for a minute 

 exactly on the center of the letter N ia the middle 

 of the word; after clofing ray eyes* and (hading 

 them fomewbat with my hand, the word was di 

 ttndtly feen in the fpedlrura io yellow letters on a 

 blue field ; and tken, on opening my eyes on a yellow* 

 ifh wall at tweo.ty feet diftance, the magnified name 

 of BANKS appeared written on the wall in golde 

 characters. 



IT was bferved by the leaf tied IVL Sauvage (N- 

 fol. Method. 1. VIII. OrcL j.) that the pulfations 

 of the optic artery might be perceived by looking 

 attetttnrdy on a ^-hite wall w^tl illuminatfid, A kind 

 of metrWorktfa&jep thao the oilier paris of the wall, 



appear* 



