C *428 ) 
ftill in Fig 5. where the Quadrilateral flatnefs is defcribed 
by V between S and T, but you rauft fuppofe that the 
difference of this and the foregoing Figure is only caufed 
by the Objects not being placed direftly before the fight, 
fo that one could only fee them the fhorteft way 3 for if 
you fuppofe that both the Divifions, as they are defcribed 
by PSR and PTR, are thofe parts which are both of them 
placed in the middle of the Chryftal,and that from thence 
the Hexangular flantings which formed the point defcri- 
bed by O and Q take their beginning , the flats which 
one fuppofes to fee at PV and VR are only occafioned by 
the undermoft parts, which upon the account of the 
Tranfparency of thefe Figures are feen thro ’em, and fo 
reprefents a flatnefs, which in reality does notexift : For 
let us imagine that that part of Fig. 5. reprefented by O; 
were placed next the fight, the divifions of that Figure 
defcribed by PTS, and lying direftly in the middle of the 
Chryftal, will then be the uppermoft fide,and PSR, which 
19 likewife in- the middle of the faid Chryftal, will be the 
undermoft. 
For my further fatisfa&ion of thefe appearances, I took 
an Hexangular piece of Rock Chryftal, and drew two 
ftreaks upon it with Ink 3 one upon that part that lay 
uppermoft, and the other upon the undermoft part, and 
each of them equidiftant from the Hexangular upper point 
of the faid Chryftal 3 and then laying it before my Eyes, 
in fuch a Pofition that the (hortning of it appeared next 
the fight, the uppermoft ftreak feemed to lie much fur- 
ther from the fight than the undermoft, and fo between 
both ftreaks was reprefented a Quadrilateral flatnefs. 
Fig. 6 . WXYZ, does likewife Ihew us aChryftafline 
Silver Particle, in which the parts that lie undermoft 
WY make the Chryftal to appear quite otherwife than it 
really is: This laft Chryftalline Particle did not feem to 
be fo well formed as many of the others 3 for in that 
Hexangular Figure, of which one could fee but three 
