DOI Page / Citation link:
https://doi.org/10.11588/diglit.68888#0349
MlCROGRAPHlA.
more then A 5 so that from F to A, there is a continual inctease of heat
and consequently os rarity 5 from whence it will necelsarily follow, that
the Rays of light will be insseded or refrasted in it, in the same man-
ner as they would be in a Concave-glase 5 for the Rays GKI, G KI will
be inssecked by G K H 0 GKH^ which will easily follow from what I be-
fore explained concerning the inssexion of the Atmojphere.
On the other side, a desending vapour,or any part of the air included
by an afccnding vapour,will exhibit the same efteds with a Convex lens 5
for,if we suppose,in the former Figure,the quite contrary constitution to
that last ddcrib’d 5 that is, the ambient Air F F being hotter then any
partofthat matter within any circle, therefore the coldest partmust
necessarily be A, as being farthest remov’d from .the heat, all the
intermediate spaces will be gradually discriminated by the continuall
mixture of heat and cold, so that it will be hotter at E E, then D D, in
DDthen CC, in CC then BB, and in B B then A. From which, a like
refraction and condensation will follow 5 and consequently a lesseror
greater refradion, so that every included part will refraCt more then the
including, by which means the Rays, GK I, GK I, coming srom a Starr,
or seme remote ObjeCt, are so infieded, that they will again concurr and
meet, in the point M. By the interposition therefore of this desending
vapour the visible body of the Star, os other Objed, is very much aug-
mented, as by the former it was diminished.
From the quick confecutions of thefe two,one after another, between
the Objed and your eye,caustd by their motion upwards or downwards,
proceeding from their levity or gravity, or to the right or left,proceed-
ing from the wind, a Starr may appear, now bigger, now less, then really
it would otherwise without them 5 and this is that property of a Starr,
which is commonly call’d twinkling, or scintillation.
The reason why a Star will now appear of one colour^now of another,
which for the most part happens when ’tis neer the Horizon, may very
easily be deduc’d from its appearing now in the middle of the vapour,
other whiles neer the edge, for is you look against the body of a Starr
v/ith a Telefiope that has a pretty deep Convex Eye-glass, and lb order it,
that the Star may appear sometimes in one place,and sometimes in another
of it$you may perceive this or that particular colour to be predominant
in the apparent Figure of the Starr, according as it is more or Ids remote
from the middle of the Lens. This I had here further explain’d, but that
it does more properly belong to another place.
I (hall therefore onely add feme few Queries, which the consideration
of these particulars hinted, and so finish this Sedion.
And the first I (hall propound is. Whether there may not be made an
artificial transparent body of an exast Globular Figure that (hall so
inflest or refrast all the Rays, that,coming from one point, fall upon any
Hewijphere of it 5 that every one of them may meet on the opposite side,
and cross one another exadly in a point 5 and that it may do the like also
with all the Rays that, coming from a lateral point, fall upon any other
Hentijphere'-) for ifso, there were to be hoped a perfection of tJioptricks^
• j j and
more then A 5 so that from F to A, there is a continual inctease of heat
and consequently os rarity 5 from whence it will necelsarily follow, that
the Rays of light will be insseded or refrasted in it, in the same man-
ner as they would be in a Concave-glase 5 for the Rays GKI, G KI will
be inssecked by G K H 0 GKH^ which will easily follow from what I be-
fore explained concerning the inssexion of the Atmojphere.
On the other side, a desending vapour,or any part of the air included
by an afccnding vapour,will exhibit the same efteds with a Convex lens 5
for,if we suppose,in the former Figure,the quite contrary constitution to
that last ddcrib’d 5 that is, the ambient Air F F being hotter then any
partofthat matter within any circle, therefore the coldest partmust
necessarily be A, as being farthest remov’d from .the heat, all the
intermediate spaces will be gradually discriminated by the continuall
mixture of heat and cold, so that it will be hotter at E E, then D D, in
DDthen CC, in CC then BB, and in B B then A. From which, a like
refraction and condensation will follow 5 and consequently a lesseror
greater refradion, so that every included part will refraCt more then the
including, by which means the Rays, GK I, GK I, coming srom a Starr,
or seme remote ObjeCt, are so infieded, that they will again concurr and
meet, in the point M. By the interposition therefore of this desending
vapour the visible body of the Star, os other Objed, is very much aug-
mented, as by the former it was diminished.
From the quick confecutions of thefe two,one after another, between
the Objed and your eye,caustd by their motion upwards or downwards,
proceeding from their levity or gravity, or to the right or left,proceed-
ing from the wind, a Starr may appear, now bigger, now less, then really
it would otherwise without them 5 and this is that property of a Starr,
which is commonly call’d twinkling, or scintillation.
The reason why a Star will now appear of one colour^now of another,
which for the most part happens when ’tis neer the Horizon, may very
easily be deduc’d from its appearing now in the middle of the vapour,
other whiles neer the edge, for is you look against the body of a Starr
v/ith a Telefiope that has a pretty deep Convex Eye-glass, and lb order it,
that the Star may appear sometimes in one place,and sometimes in another
of it$you may perceive this or that particular colour to be predominant
in the apparent Figure of the Starr, according as it is more or Ids remote
from the middle of the Lens. This I had here further explain’d, but that
it does more properly belong to another place.
I (hall therefore onely add feme few Queries, which the consideration
of these particulars hinted, and so finish this Sedion.
And the first I (hall propound is. Whether there may not be made an
artificial transparent body of an exast Globular Figure that (hall so
inflest or refrast all the Rays, that,coming from one point, fall upon any
Hewijphere of it 5 that every one of them may meet on the opposite side,
and cross one another exadly in a point 5 and that it may do the like also
with all the Rays that, coming from a lateral point, fall upon any other
Hentijphere'-) for ifso, there were to be hoped a perfection of tJioptricks^
• j j and