VOL. XIII.] PHILOSOPHICAL TRANSACTIONS. 6l3 



greatest of all. 8. Whereas I mention sometimes the parallelism of the cor- 

 respondent fibres, I mean it not in a strict mathematical sense, but only their 

 being as it were in aequilibrio or due poise in respect of their situation ; and 

 therefore if those fibres had been straight, and not of a curved figure as they 

 are, I should have rather chose to have expressed my mind by the phrase of 

 mathematicians, of their being in eodem piano. But my sense being under- 

 stood, there need not be any exception to the word, since it was not so easy to 

 express my meaning by a better; and therefore I shall pass by this, and proceed 

 to more real objections that have been sent me by Mr. Newton, our worthy 

 professor of mathematics at Cambridge, and other friends, relating to the opi- 

 nion itself. 



The 1st objection was made in the Royal Society when it was read there 

 which it seems was this; viz. That it seemed difficult to conceive how those 

 soft medullary fibres of the nerve could have such a tension. But this is not 

 harder to conceive than in that of a spider's web, whose mucous substance and 

 expansion very well answer to that of the retina; and as the least breath of 

 wind moves the one, so the least gale of the ethereal or lucid matter causes a 

 vibration in the other. Further it was objected, that it was hard to conceive 

 how so soft a body as the thalamus opticus could make such a difference in the 

 stress or tension of the fibres. But it is apparent, that on drawing the nerve 

 from it forward, the superior fibres are more on the stress than the lateral, and 

 nature in these cases is finer in her operations then we are in our conceptions of 

 them. It seems so especially in the formation of this organ. 



2. It has been objected by others, that if the superior fibres were more tense 

 than the inferior, we should see better by rays falling on the top than the bot- 

 tom of the eye, or see an object better placed below our eye, when the rays 

 passing in a straight line from it must terminate in the top fibres, than above it, 

 when they must terminate in the lower fibres. To this I answer, that it does 

 accordingly fall out so, and this is a more positive and direct proof of my opi- 

 nion ; for I appeal to any man's experience whether the characters in a book ap- 

 pear not better to him, or he reads not better in it, held about half a yard un- 

 der his eye than so much above it; or whether he does not more readily discern 

 or find out objects beneath than above him with the same light : and this may 

 be further illustrated by my Lord Bacon's experiment, of a man's appearing 

 better on the ground to him that is placed on a high steeple, than vice vers^. 



3. It is urged that according to my scheme of the situation of the correspond- 

 ent fibres, the rays of an object placed laterally, suppose toward the left eye, 

 could not fall on the fellow fibres in the right eye ; for if it were placed slant- 

 ingly toward the left eye, the rays could not fall on the internal lateral fibres of 



