the Disk of the Sun near the Horizon. 489 



is observed, the sun and moon are determinately red or red- 

 dish orange. It next flashed across my mind that I had some- 

 where read that Fraunhofer on one occasion had remarked, while 

 engaged in examining the spectrum from end to end, that the 

 focal distance of the telescope required to be shortened to a far 

 greater extent than could be accounted for by the refrangibili- 

 ties. Could then the eye itself be thus singularly affected ? 

 It appeared to me there were present two unquestionable facts 

 — a dilated condition of the pupil, and a striking predominance 

 of red rays. Were these conjoined in the production of the 

 phenomenon ? It has long been known that certain peculiarities 

 attach to the red ray : it possesses an extraordinary quality for 

 exact definition, it penetrates to vast depths of sea, it can 

 be discerned when no other colour can be seen, and a distin- 

 guished physicist informs me that its long-continued use in phi- 

 losophical investigations produces on the retina an effect border- 

 ing on amaurosis. Is it not possible, then, that the eye may be 

 affected in certain states of vision in a way that would prepare 

 us for abnormal results? A consideration of the subject led mefirst 

 to the remarks contained in Phil. Mag. for December, p. 425 ; 

 but having reached so far, no opportunity occurred for my testing 

 the conjectures which I formed by observing the sun or moon, 

 when augmented, through small holes pierced in a metal plate, 

 until the 24th inst., when the moon favoured me with a trial. 

 As I transferred my eye from hole to hole (beginning with the 

 largest), the diameter became less and less, and the ruddy hue 

 less obvious, till I reached a size (its ordinary size) when the 

 holes diminished it no further, the only effect through the smaller 

 holes being a diminution of brightness from exclusion of more 

 and more rays. Trees and other objects glanced at were un- 

 affected by these holes in their relative distances, being only ren- 

 dered a little more obscure than when looked at directly. I 

 shortly afterwards examined stars through the holes, and found 

 that they lost their spurious disks and became mere points, re- 

 markably ceasing to twinkle, the residuary effect on the retina 

 appearing to be due to intensity of light as contradistinguished 

 from quantity of light. I am most anxious that these observa- 

 tions should be repeated : in Ireland it is rare to find oppor- 

 tunities, and shall be glad to find in your pages communications 

 confirming or modifying the results I have myself arrived at. 



Yours faithfully, 



Robert Templeton. 



P.S. While the proof of the above was in my hands, I tried 

 various combinations of coloured plate glasses, but could not 

 succeed in augmenting the disk to more than double size : the 



