. Notices respecting New Books. 379 
to twice the products of those terms taken two and two. All 
the instances accompanying the rule are too long for insertion, 
but we have selected one. 
at—4a?h + Sab? + 4b4 
a*—2al — 2)? — 0. square root, 
Here the root of the first term a+ is a*, which we place in the 
quotient; secondly, we multiply this root by 2, giving for a pra- 
duct 2a*, by which we divide the second term —4a’); the quor 
tient is —2al, which we place under the second term ; thirdly, 
—2abx2=4ah and +Sal?— —4al gives —2l* for the third 
term; lastly, —2b? squared =-+4b4, which subtracted from the 
last term leaves nothing. ‘Therefore the square root is a*— 
2ab —2b7—0. 
LXIV. Notices respecting New Books, 
A Letter to Professor Srewant, On the Objects of General 
Terms, and on the Axiomatical Laws of Vision. By J, FEARN, 
Esq. pp. 32, 
Oy the two subjects treated in this letter, the author states the 
latter, on the Axiomatical Laws of Vision, to be that to which 
he is more particularly desirous of attracting public attention. 
The matter of the Laws of Vision he presents as exhibiting what 
he considers to be a mathematical analysis of the constituents or 
cause of VisipLE Figure; and‘as falling properly enough within 
our range of philosophical duty, to contribute to the general in- 
vestigation of a view certainly somewhat novel of an interesting 
branch of physics, we shall extract at length that part of the 
letter which relates to it. 
* ON THE AXIOMATICAL LAWS OF VISION. 
Preface. 
** The most proper preface to the following subject, on the 
present occasion, appears to be that of introducing the fact as- 
serted by Proclus [alluded to in the address prefixed to this 
publication], In stating this fact, however, it may be of no 
small consequence to note, very particularly, that although its 
truth must attest the truth of the Jaws of vision, (which is my 
reason for bringing it forward here,) yet if the fact could be ac- 
tually disproved, this could not at all affect these laws, since 
they do not depend upon, but include, the fact asserted by 
Proclus. Yet, nevertheless, I must add, that I believe my- 
self to have distinctly proved the fact in question; which, it 
is to be remarked, is not proved by Proclus, but only asserted by 
him, : : 
“In 
