VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. SQQ 



all eyes, even those which are adapted to distant objects. If this attempt to 

 show the compatibility of the actual distinctness of our sight with the different 

 refrangibility of light be admitted as just and convincing, we shall have fresh 

 reason to admire the wisdom of the Creator, in so adapting the aperture of the 

 pupil and the different refrangibility of light to each other, as to render the 

 picture of objects on the retina relatively, though not absolutely, perfect, and 

 fitted for every useful purpose; " where," to borrow the words of our religious 

 and oratorical philosopher Derham, " all the glories of the heavens and earth 

 are brought and exquisitely pictured." 



Nor does it appear, that any material advantage would have been obtained, if 

 the image of objects on the retina had been made absolutely perfect, unless the 

 acuteness of the optic nerve should have been increased at the same time; as the 

 minimum visible depends no less on that circumstance than the other. But that 

 the sensibility of the optic nerve could not have been much increased beyond 

 what it is, without great inconvenience to us, may be easily conceived, if we 

 only consider the forcible impression made on our eyes by a bright sky, or even 

 the day objects illuminated by a strong sun. Hence we may conclude, that such 

 an alteration would have rendered our sight painful instead of pleasant, and 

 noxious instead of useful. We might indeed have been enabled to see more in 

 the starry heavens with the naked eye, but it must have been at the expense of 

 our daily labours and occupations, the immediate and necessary employment 

 of man. 



To obviate an objection to the diffusion of the rays on the retina by the dif- 

 ferent refrangibility of light, it may be said, that the ocular aberration, being a 

 separate cause from any effect of the telescope, should subsist equally when we 

 observe a star through a telescope as when we look at it with the naked eye; 

 and that therefore the fixed stars could not appear so small as they have been 

 found to do through the best telescopes, and particularly by Dr. Herschel with 

 his excellent ones. To this Dr. M. answers, that the ocular aberration, which is 

 proportional to the diameter of the pupil when we use the naked eye, is pro- 

 portional to the diameter of the pencil of rays at the eye when we look through 

 a telescope, which being many times less than that of the pupil itself, the ocular 

 aberration will be diminished in proportion, and become insensible. 



XXII. Experiments and Observations on Electricity. By Mr. William Nichol- 

 son, p. 265. 



Mr. N. divides this paper into 3 sections. 1st. On the excitation of electri- 

 city; 2d, On the luminous appearances of electricity, and the action of points; 

 3d, Of compensated electricity. 



1 . A glass cylinder was mounted, and a cushion applied with a silk flap, pro- 



