( 747 ) 
organ of vifion ; undertaking to anfwer thofe Reafonsand Ex^ 
periments, that have been a Hedged by Moniieur ^armte and 
Monfieur JPicard in favour of the Chormdes. 
Having done with the tunkles , he paiTes on to the Humm^ 
and renders a i eafon of iheir different denfity. Then be afiigos 
the life of the Jqueous humor; and recites a remarkable cafe 
of an Old mansSighc reftored ; who being feventy years of 
age, and having ufed Speftacies for the fpace of ten yeats^had, 
upon taking a great cold, this humor fo repaired^ thar^v\hen the 
Author wrote this Difcourfe^ that Ancient man had then for 
the time of fix years ufed no Speflacles acall , but been able 
without them to read the fmalleft print. 
Speaking of the Cryftallin humor, he obferves, that the ante- 
rior part thereof, in Man and Quadrupeds , refembies the feg- 
ment of a greater Ellipfe , and the pofteriorj that of a fimller, 
thacfo the rays being duly refrafted may pafsas they ought 
into the retim : Whereas in Fijhes the figure of this humor is 
more globous , to the end that it might «the more refraft the 
rays, which pafljng through water, as a medium of the like 
denfity with it, would otherwife not acquire their due refra- 
ftion. As to the F/Vy<?i?«i humor , he judges it to be of that 
nature, that being once loft, it caf$ «ri/^r/^^repairedjwhatever 
Kerckringius do pretend to the contrary ^ though our Author 
thinks, the jiqt^epus humor mnLy» The life of thefe Humors 
appears in this, that vifion chiefly depends from the refraflion 
of the rays tranfmitted through ttiefe humors. 
Next, he treats of the Arteries , fem]^ and N'erves of the 
Eyes, together with the Motion of the Jmmal (pirtts in them. 
Here, among other particulars, hefliews , rhac i: he Fibres of 
the Optic Nerve about the place of their union are not at all 
confounded, but run on from the Brain diftinftly^ as alfo^ 
that when the nervi motorii near the infundibuJum are by fome 
fharp humor irritated , the Eyes will be thereby convul fed 5 
concerning which he relateth a remarkable inftance of a young 
man that died of fuch a convulfion. As to che Motion of the 
jinimd Jpirits in the Mufcles of the Eyes and in the Optic 
Nerve , he conceives, that, when that is gentle and eveb , we 
apprehend things diftinftly ; buc when 'cisuneven and defui- 
tory, we then have confufed phantafmsof things^ as It hap* 
peas to young TobacGonifts and young Navigators ^ growing 
