214 M E M O I R S of the 
him eafily conclude, that the brain muft be prefTed down thither, 
which he was the more induced to believe, becaule the mother 
told him, that when (lie was with child, fhe received a coniider- 
able bruilc in the belly. 
How far the Medulla fpinalis may anfwer the office of the 
brain, elpccially in embryos, where there is no exercile of the 
lenfes, nor of the imaginative faculty, will be no great difficulty 
to apprehend j fince the fpirits generated even in the Akdidla 
Jpinalis may fuffice for all the fundions of life in them 5 efpecially 
in this inftance, where a great part of the brain is fuppofed to be 
detruded into the cavity of the Vertebrce , and it may be que- 
ried, whether in thofe inftances, that are given of births of in- 
fants without brains, there might not be a like depreffion thereof 
or of its principal parts into the VertehrdS^ which in embryos arc 
parts capable of extenfion. 
An Optic Leas of JVater, and a refieBlng Microfcope^ l^y 
Mr. Stephen Gray. Phil. Tranf. N° 228. p. 539. 
DROPS of fair water, being let fall on a piece of plain 
glafs, form themfelves into plano-convexes, having a con- 
vexity proportional to the heights from which they defcend 5 viz. 
from a greater height a lefs, and from a lefs a greater degree of 
convexity. Mr. Gray applied fome of thefe as reading-glafles 
for fingle words of Imall letters, as on globes and maps,' and he 
found no other inconvenicncy, than that the fluidity of the water 
obliges one to keep the glais horizontal j to remedy which, he 
took a fufficicnt quantity of ifing-glais, and diiTolved it in water 
over the fire, and whillt it waS warm, he dipt a Itick into the 
folution, and let fome drops of it fall on the glafs as before, and 
in a quarter of an hour they acquired a confiftency, that fuftlred 
them to be held in any pofition j and tho' they were not altoge- 
ther lb tranfparent, yet this was little or no impediment to their 
ufe. The drops ot this Iblution are more accurately defined than 
thofe of common-water, having their edges exa6tly circular, and 
they may be made of a much longer Focus. 
A thin flat ring of brals, not exceeding to <>f an inch diameter 
in its inrenor circle, being cemented to a plain piece of glals, and 
filled with water, or the folution now mentioned, then prefling 
with the finger into it, till what is fupcrfluous be taken oft^ there 
will be formed a plano-concave, which may ferve as an eye -glafs 
to a prolpcctive, or to any other optical ufe, concave glaffes are 
applicable to. 
Mr. Gr^iy 
