C 4058 ) 
lyformed^yet would only refled: thofe rays truly, which re- 
fpe(Sl ihe axtr, 5 7 he errours of the faid convex will be much 
augmented by the too great diftance, through which the rays , 
refled:ed from it , muft oafs before their arrival at t^ie Eye- 
glafs. For which reafon i find it convenient to make the Tube 
lio wider than IS nccelTary, that the Eye glafs be placed as 
near to the Oval plane^ as is poffible, without obftruding any 
nfef ul light io its paflage to the objecS metal* 4, The errors oi 
the objcd-metal will be more augmented by reflexion from 
the coij vex than from the plane^ becaufe of the inclination or 
deflexion of the convex on all fides from the points, on which 
every ray ought to be incident. 5» For thefe reafons there is re- 
qu-fuean eKtraordioary exacStnefs in the figure of the little 
C6r,v Xj whereas I fiad by experience , that it is much more 
difficult to communicate an exad figure to fuch fmall pieces of 
Metal, than to thofe that are greater* 6 Becaufe the errors at 
the perimeter of the concave Objedl- Metal , caufedby the 
Sphericalnefs oftts figure^are much augmentedby the convex, 
it will not with difl:in(flnefs bear fo large an aperture^as in the 
other conftruftion. By reafon that the little convex condu- 
ces very much to the magnifying virtue of the inftrument, 
which the Oval plane doth nor^ it will magnify much more in 
proportion to theSphere^on which the greatconcaveis ground, 
than in f he other defign^ And fo magnifying Objefe much 
more than it ought to do in proportion to its aperture,it muft 
reprefent them very obkure and dark > and not only fo, but 
alfo confufed by reafon of its being overcharged. Nor is 
there any convenient remedy for this. For, if the little con- 
vex be made of a larger Sphere , that will caufe a greater in- 
convenience by intercepting too many of the beft rayes ; or,if 
the Charge of the Eye-glafs be made fo much fliallower as is 
neceffaryjthe angle of vifiou will thereby become fo litrie^thac 
it will be very difficult and troublefome to find an objed:, and 
«5f that objed:> when fouud^ there will be but a very (mall part 
leenatocce. 
By this you may perceive^ that the three adrantagesj which 
MonfiQuxCdjpgrmn propounds to himfelf, are rather difad. 
vantages* For, according to his defign, the aperture of the 
iuftrumenc 
