16691 
to 'make a due agreement with that other glafs- But 
to obferve the Moon, there needs nothing of this^ when 
the glafs eafily may be difcovered by the Moon hght it felf. 
Thtrdij^ it is very difficult to find (in fiich a length of a Tube 
of loo or ico foot) the true parallelifm of the two glaffes, 
the ftring being bended in the middle, and alfo not fit to 
give a true or ftrait diredion. To this he anfwereth r- that 
there is no need of fuch a geometrical perfe£lion of pa- 
rallelifm, but that the fame may have fome latitude. 
The ftring being of a fmall weight, and only a filk 
thred, which p foot long doth fcarce amount to haifea 
drachm, and yet able to hold / of weight, this bending of 
the ftring will caufe only a fmall errour, for to find how 
much the bending raaketh it dechne, if it is fuppofed to 
be a. parabohcal hne in the curvature, the angle of de- 
fledlion by the tangent will come to 14 mi nuts which in 
lyofoot diftance produceth an errour of one foot, that 
the Eye will be out of her true way of direction. 
But to remedy all this, he iheweth how by the help of 
the Lanterne fuch .miftakes may be corrected- FQnnhly^ 
the conftitution of the air, as being windie, or tempeftu- 
ous will make a great hindrance, for the ftring or cord 
will be altered and drawn at one or the other fide. To 
prevent this, there is no remedy: the common fort of 
Telefeopes being fubjedt to the fame troubles. Yea fome- 
times, when the air is very quiet and the 6 ky clear, yet 
the ftars much glittering, the Telefeopes will not ferve, al- 
fo the vapours fometimes will ftic*<: to the glafs. Fifthlj, againft 
the lantern before mentioned, one migiit objedt that at a di- 
ftance of ^00 and more foot, the light projected would 
be very weak, and not well to be difcerned : but to make it 
brighter, a greater lantern muft be got and a bigger wick 
put in, and other things ordered accordingly Sixvidy^ifit: 
mould be too troublefome to, to fix fuch a long maft of a 1 00 
and more foot, the Author fheweth how the compofition of 
mafts joyniog one to another may be continued as far as ne- 
ceffity fhall require- Yet for all that, he thinks, there will 
be no neeci to make thefe malts of fuch a vaft height : for no 
body will bring the Telefeopes to foch a perfection as to 
make appear any animal or creature in the Moon or Planets. 
Becaule, firft, there is fuch a difficulty in making the glaf- 
fes, for the bigger they are, the more art is required in per- 
forming theiiv 2- There is . fcarce any piece of giafs to be ■ 
found fit for fuch a large bufinefs, being peitered with many 
faults. 3. The amplification of the things feen by Tele- 
feopes being regulated by the biguefsof the aperture that 
