DOI Page / Citation link:
https://doi.org/10.11588/diglit.68888#0029
The Preface.
may not singe or burn the Paper. Instead of which Paper there maybe
made use of a sinal! piece of Looking-glass plate , one of whose sides is made
rough by being rubb’don aslat Tool with very fine (and, this will, if the
heat be leisurely cast on it, indure a much greater degree of heat, and con-
sequently very much augment a convenient light. By all which means the
light of the Sun, or of a Window, may be so cast on an Object, as to make it
twice as light as it would otherwise be without it, and that without any in-
convenience of glaring, which the immediate light os the Sun is very apt to
create in mosr Objects, for by this means the light isso equally diftused,
that all parts are alike inlightned ; but when the immediate sight of the Sun
falls on it, the ressexions from seme few parts are sb vivid, that they drown
the appearance of all the other, and are themselves also, by reason of the in-
equality of light, indistinst, and appear only radiant spots.
But becaule the light of the Sun, and also that of a Window, is in a conti-
nual variation, and so many Objects cannot be view’d long enough by then!
to be throughly examin’d 5 besidesthat, oftentimes the Weather is so dark
and cloudy, that for many dayes together nothing can be view’d: And be-
cause also there are many Objects to be met with in the night, which cannot
so conveniently be kept perhaps till the day, therefore to procure and cast a
sufficient quantity of light on an Objed in the night, I thought of, and often
used this, Expedient.
I procur’d me a small Pedestal, sitch as is describ’d in the fifth Figure os
the first Scheme on the small Pillar A B, of which were two movable
Armes CD, which by means of the Screws E F, I could fix in any part of
the Pillar 5 on the undermost of thefe I plac’d a pretty large Globe os Glass
G, fill’d with exceeding clear Brine, stopt, inverted, and fixt in the manner
visible in the Figure 5 out of the side of which Arm proceeded another
Arm H, with many joynts 5 to the end of which was fastned a deep plain
Convex glafs I, which by means of this Arm could be moved to and fro, and
fixt in any posture. On the upper Arm was placed a small Lamp K, which
could be so mov’d upon the end of the Arm , as to be set in a fit posture to
give light through the Ball: By means of this Instrument duly plac’d , as is
exprest in the Figure, with the sinall ssame of a Lamp may be cast as great
and convenient a light on the Object as it will well indure,and being always
constant, and to be had at any time. I found most proper for drawing the
reprefentations of thofe small Objects I had occasion to observe.
None of all which ways (though much beyond any other hitherto made
ufe of by any I know ) do afford a sufficient help, but after a certain
degree of magnifying,they leave us again in the lurch. Hence it were very
deserable, that feme way were thought of for making the Ob jed-glass of
such a Figure as would conveniently bear a large Aperture.
As sor Telescopes, the. only improvement they feem capable of rs the
increasing of their length ; for the Objedbeingremate^ there hs no thought
°s n greater light then it ha^; and therefore to augment the
Aperture., the Glasi mu ft be ground of a very large fyhere ; for^by that
e mean^
may not singe or burn the Paper. Instead of which Paper there maybe
made use of a sinal! piece of Looking-glass plate , one of whose sides is made
rough by being rubb’don aslat Tool with very fine (and, this will, if the
heat be leisurely cast on it, indure a much greater degree of heat, and con-
sequently very much augment a convenient light. By all which means the
light of the Sun, or of a Window, may be so cast on an Object, as to make it
twice as light as it would otherwise be without it, and that without any in-
convenience of glaring, which the immediate light os the Sun is very apt to
create in mosr Objects, for by this means the light isso equally diftused,
that all parts are alike inlightned ; but when the immediate sight of the Sun
falls on it, the ressexions from seme few parts are sb vivid, that they drown
the appearance of all the other, and are themselves also, by reason of the in-
equality of light, indistinst, and appear only radiant spots.
But becaule the light of the Sun, and also that of a Window, is in a conti-
nual variation, and so many Objects cannot be view’d long enough by then!
to be throughly examin’d 5 besidesthat, oftentimes the Weather is so dark
and cloudy, that for many dayes together nothing can be view’d: And be-
cause also there are many Objects to be met with in the night, which cannot
so conveniently be kept perhaps till the day, therefore to procure and cast a
sufficient quantity of light on an Objed in the night, I thought of, and often
used this, Expedient.
I procur’d me a small Pedestal, sitch as is describ’d in the fifth Figure os
the first Scheme on the small Pillar A B, of which were two movable
Armes CD, which by means of the Screws E F, I could fix in any part of
the Pillar 5 on the undermost of thefe I plac’d a pretty large Globe os Glass
G, fill’d with exceeding clear Brine, stopt, inverted, and fixt in the manner
visible in the Figure 5 out of the side of which Arm proceeded another
Arm H, with many joynts 5 to the end of which was fastned a deep plain
Convex glafs I, which by means of this Arm could be moved to and fro, and
fixt in any posture. On the upper Arm was placed a small Lamp K, which
could be so mov’d upon the end of the Arm , as to be set in a fit posture to
give light through the Ball: By means of this Instrument duly plac’d , as is
exprest in the Figure, with the sinall ssame of a Lamp may be cast as great
and convenient a light on the Object as it will well indure,and being always
constant, and to be had at any time. I found most proper for drawing the
reprefentations of thofe small Objects I had occasion to observe.
None of all which ways (though much beyond any other hitherto made
ufe of by any I know ) do afford a sufficient help, but after a certain
degree of magnifying,they leave us again in the lurch. Hence it were very
deserable, that feme way were thought of for making the Ob jed-glass of
such a Figure as would conveniently bear a large Aperture.
As sor Telescopes, the. only improvement they feem capable of rs the
increasing of their length ; for the Objedbeingremate^ there hs no thought
°s n greater light then it ha^; and therefore to augment the
Aperture., the Glasi mu ft be ground of a very large fyhere ; for^by that
e mean^