380 Notices respecting New Books, 
“*In Mr, Taylor’s translation of the Commentaries of Proclus 
on the first book of Euclid’s Elements, vol. i. page 125, is this 
passage: ‘ We should admit the followers of Apollonius, who say, 
that we obtain the notion of a line when we are ordered to mea- 
sure the lengths alone, either of ways er walls; for then we do 
not subjoin either breadth or bulk, but only make one distance 
the object of our consideration. But a line may become the ob- 
ject of our sensation, if we behold the divisions of lucid places 
from those which are dark, or survey the moon when dichoto- 
mized ; for this medium has no distance with respect to latitude, 
but is endued with longitude, which is extended together with 
the light and shadow.’ 
** The perspicuity of the description of this fact is highly con- 
clusive and valuable. But I cannot avoid remarking, how 
strange it appears that any philosopher who had adverted to this 
fact in the particular instances of ¢ the divisions of lucid’ places 
from those which are dark,’ should not have intuitively discerned 
that the principle is general, universal, and sole: which it must 
be, since light and contiguous shadow produce in us (wo sensa- 
tions of colours with a line beiweeu them, just as is ‘arid must 
be done by any other two colours whatever.—His not discerning 
the universality of the fact was the only thing that could have 
kept Proclus from advancing on, to discern the four Jaws of vi- 
‘sion and their axiomatical nature, together with their direct 
consequences, 
*¢ OF THE EXTERNAL CAUSE OF VISION. 
“1. Distant bodies are not, by any medium, the generic cause 
of vision; since sensations of colours, accompanied by Jigures, 
are as constantly, and as variously, excited by experiments of 
pressure upon the eye, and by other bodily affections, as they 
are by light reflected from distant objects. 
“* This general fact, being duly recognised, ascertains of itself 
the independence of vision upon external dis/ant bodies, and re- 
moves a very great and most pernicious stumbling block, which 
has strangely been suffered to remain an obstacle to all advance- 
ment, although uniform experience has long demanded its ex- 
pulsion from the subject. 
*¢ 2. When the optic organ is stimulated, either by light, by 
sensible pressure, by certain bodily diseases, or by any other such 
impulse, the mind undergoes a set of sensaliors called colours, 
Such are those beautiful phantoms that appear to us when we 
look at a rainbow, or a landscape. These phenomena seem to 
ailhere to external distant objects, like a skin cast over them : 
but there is no fact upon which philosophers are more unani- 
mous, than that they are nothing but our own sensations. It is 
therefore 
