( Soi ) 
In order to fupporthis Hypothefesof Mediums like 
Veils to alter the Colours of Objetts looked at , he 
“ confiders (Preface, Page 31.) the Images in the Eye 
“ as an Objed looked at, which would be fuppofing 
“ other Organs of Vifion to look into the Eyes”— 
whereas the Pidures of external Objeds fhewn upon 
the back Part of an Eye placed in an Hole in the Win- 
dow of a dark Room, are only fuch to thofe who fee 
the Experiment j but in the Animal who fees, thofe 
Pidures are a great Number of fmall Blows or Impref- 
fions made upon the Fibres of the Retina by the Irn- 
pulfe of many Rays colleded in the Vertices of the 
Cones of Light within the Eye, correfponding with fo 
many other Cones which proceed from the vifible 
Points of external Objeds, and make, what Opticians 
call Pencils of Rays. 
« That the Jlefiftance of Water from its Tenacity is 
« greater than from its Denfity. . 
“ That fince a fmall Thread, half blue and half red \ 
« is feen diftindly by the naked Eye, that Phamome- 
« non overthrows the Dodrine of different Refran- 
« gibilityl ’ But here the Author does not conlider, that 
the Focus of the Eye is fo Ihort that the Diftance of the 
diftind Bafe ©f the bine and th t~red Image of fuch 
Threads is not equal to the Thicknefs of the Retina . 
“ That the Experiment of the two-coloured Paper 
u projeding its Image through a Lens (which I repeat. 
w ed in the Manner above-mentioned, in the Year 
u lyzz) did fometimes fucceed with him, andfome- 
“ times not} and therefore that it did not prove the dif- 
“ ferent Refrangibility of Rays ; But the different 
“ Place of the diftind Bafe of the blue and the red 
a Image, was to be afcribed to the different Inclina- 
“ tion 
