_Thermometers_, _Barometers_, _Hygroscopes_.
These Observations being thought very considerable as well as curious, 'tis
hoped, that those who have conveniency, will give encouragement and
assistance for the making of them; and withall oblige the publick by
imparting, what they shall have observed of this kind: The _Publisher_
intending, that when ever such observations shall be communicated to him,
he will give notice of it to the _publick_, and take care of the
improvement thereof to the best use and advantage. A _Pattern_ of the
_Table_, proposed to be made for observing the _Tides_, is intended to be
published the next opportunity, God permitting.
* * * * *
_An Account of Several Books lately published_
I. _Johannis Hevelii DESCRIPTIO COMETAE, Anno AErae Christianae MDCLXV. exorti;
una cum MANTISSA Prodromi Cometici, Observationes omnes prioris COMETAE
MDCLIV, ex iisque genuinum motum accurate deductum, cum Notis &
Animadversionibus, exhibens._
This Book (as the Title it self intimates) undertakes two things. _First_,
To give an Account of the _Second_ of the two late Comets, which appeared,
when the _other_ was scarce extinct; Concerning which, the Author doth,
from the Observations made by himself with a _Sextant_ of 6 foot, and
divided into _minutes_ and _seconds_, assign _both_ its true place (as well
in respect of the _Ecliptick_ as the _AEquator_) _and_ its proper motion;
Adding a fair Delineation of its Course, together with the genuine
Representations of its _Head_ and _Train_, in each day of its apparition;
and subjoyning a General Description and Discourse of some of the more
notable _Phenomena_ thereof. It was first seen at _Dantzick_ by the
Watchmen, the 5th of _April_ st. n. 1665. and then observed by the _Author_
from _April_ 6, about 11/2 of the Clock in the morning, till _April_ 20 at 3.
in the morning. During which time, it went with a reasonable velocity;
making 46 deg. in its Orb, _according to the Order of the Signs_, moving
from the _Breast_ of _Pegasus_, towards the _Head_ of _Andromeda_, and the
_Left Horn_ of _Aries_; having, as 'tis presumed, taken its rise from above
_Sagittary_, and run through the _Breast_ of _Antinous_, under _Aquila_ and
the _Dolphin_, to the said _Pegasus_; and so on, as is already expressed.
The _Head_ of it is in the Book described of a Colour like that of
_Jupiter_, all along much brighter than that of the former Comet, though of
a somewhat less magnitude; having in its middle onely _one_ round, but very
bright and big _Kernel_ or Speck, resplendent like Gold, and encompassed
with another more dilute and seemingly uniform matter: its _Tail_ being at
first, about 17. deg. and afterwards 20. and sometimes 25 deg. long, and
divaricated towards the End.
_Next_, it is observed, that though this Star did afterwards slacken its
pace, yet it retained the vividness of its Colour, both of the _Head_ and
_Train_; the _Head_ especially, keeping at the time as well of the last
observations, as of the {302} first, the brightness of its single _kernel_,
though the environing more dilute matter were then almost all lost; it
being, according to the Author, more and more attenuated, and grown narrow,
the nearer the Star approached to the Sun.
_Thirdly_, 'tis noted, That this _Comet_ did very much digress from the
_Hypothesis_, delivered by _M. Auzout_, in regard that, whereas according
to that _Hypothesis_, this Star should not arrive to the _Ecliptick_ till
after the space of 3 months, it arrived there the 28 of _April_. And then,
that its first Conjunction with the Sun hapned between the 19 and 20 of
_April_, and the second, the last of _April_, not (as _M. Auzout_, would
have it) the 15 of _May_. So that he concludes, that this Comet never came
down to the _Pleiads_ and the _Eye of Taurus_, as the Hypothesis of _M.
Auzout_ requires, but that from _April_ 20. it did immediately take its
course towards the Ecliptick, deflecting every day more and more from the
_Section_ of a _Great Circle_, to the _Lucida_ of _Aries_, arriving at the
_Ecliptick_ the last of _April_, about the 8th or 10th deg. of _Taurus_;
not in _July_ about the 8th of _Gemini_, and the _Eye of Taurus_.
_Fourthly_, He intimates, that if this Comet had appeared some weeks
sooner, it would have confronted the former Comet, being yet in its vigour
and of a conspicuous bigness, in the same place, where that was, viz. the
_Head of Aries_.
_Fifthly_, He observes, that this Star in progress of time became
_Retrograde_, whence it came to pass, that in the Months of _June_ and
_July_ it did not appear again before the Rising of the Sun, though the Sun
left it far behind: whereas, if it had proceeded toward the _Eye of
Taurus_, it would have appeared again in the morning.
_Sixthly_, He maintains, that this Comet was not the same with the former;
which he thinks may be demonstrated, onely by a due Delineation of both
their Course upon the _Globe_; where he saith it to be evident, that the
former could never come to the _Head_ of _Pegasus_, as moving already in
_February_ in a streight Course about the _Head_ of _Aries_; Besides, that
the _former_ went in the very beginning in a _Retrograde_ motion; but
_this_ perpetually in a direct one: _that_, about the end, very slow, its
Head lessning and growing dark; _this_ swift enough, with its head
conspicuous and bright. To which he adds, that the whole Course of the
former was made under a quite different _Angle_ of the _Orbite_ and
_Ecliptick_, and a different Motion of the _Nodes_ from the latter: As also
that their _Faces_ differed very much from one another; the _first_
exhibiting all along a matter, which as to its density and rarity, altered
from day to day exceedingly, whereas the _second_ retained (to the Authors
admiration, who affirms, never to have observed the like) all the time he
saw it, one and the same round, dense and bright Speck or Kernel.
All which he concludes 1, With an Intimation of his sense concerning two
other Comets, pretended to have been lately seen, _One_ at _Rome_, about
the {303} _Girdle of Andromeda_, in the Months of _February_ and _March_,
1664. the other in _Germany_ in _Capricorne_, about _Saturne_ in the head
of _Sagittary_, during the Months of _September_ and _October_, 1665. 2ly,
With an Advertisement of what he has done in that important Work for the
Advancement of _Astronomy_, the due _Restitution of the Fixt Stars, vid._
That he has almost finish't it; himself alone, without trusting to any
other mans labour, that was not directed by him.
The _Second_ Part of this Book (the _Mantissa_ to the _Prodromus
Cometicus_) endeavours to justifie the Authors Observations touching the
former Comet, excepted against by M. _Auzout_, in several particulars; as
1. That it had not pass'd to the _First_, but _Second_ Star in _Aries_, and
had mov'd in quite another Line, than He had described. 2. That its _proper
motion_ about the end of _January_ and the beginning of _February_, 1665.
had not been rightly assigned. 3. That the _Bignesse_ of its _Diameter_ had
not been truly delivered; Nor 4. The _Faces_ of its _Head_ in due manner
represented.
To all which the Author endeavors to answer: 1. By delivering all his
Observations of that Comet, thereby to shew, what care and diligence he had
used, _particularly_ to make out, how great its _Diurnal motion_ had been;
in what proportion, and how far, it decreased, and where and in what degree
it increased again: Which being, as he conceives, duly and exactly deduced,
and demonstrated, he esteems it afterwards to be easie for every one,
versed in these matters, certainly to collect and to judge, what way the
Comet, after it became invisible to the naked Eye, and could be no longer
observed with _Sextants_ and _Quadrants_, had taken, and what Line it had
described. 2, By subjecting all those Observations, with great diligence
and labour, to a rigid _Calculus_, thereby to obtain, for every day, the
_Longitudes_, _Latitudes_, _Right Ascensions, Declinations_, _Proper
motion_, _Angle_ of the _Ecliptick_ and the _AEquator_, and the _Nodes_ of
that Comet; for the construction of an _Ephemerides_ of its whole Motion.
From all which he pretends to prove, that he has not erred in his
Observation of _February_ 18, nor been prepossest by any _Hypothesis_, nor
deluded by any _Fixt Star_, as M. _Auzout_ thinketh; but that near the
_First Star_ of _Aries_ there _then_ appear'd a _Phaenomenon_, most like to
that Comet, that was seen some dayes before, if compared with the
Observations make thereof _Febr._ 12, 13, 14. Though he will not hitherto
positively determine, whether that _Phaenomenon_, which appear'd to him
_February_ 18. was {304} indeed that very Comet, which he saw with his
naked Eye, and observed with his Geometrical Instruments, the said 12, 13,
and 14. dayes of _February_; or whether it was another, and whether he had
lost that Comet, which moved towards the _Second Star_ in _Aries_: but
leaves it to the Learned World, and particularly to the _Royal Society_,
after they shall have well examined and considered all his Observations,
and the _Calculus_ raised therefrom, to judge of this, and the other
particulars in controversie.
II. _Isaacus Vossius de NILI et ALIORUM FLUMINUM ORIGINE_. It was _Numb._
14. of these _Transactions_, that gave an account of the _Cause_ of the
_Inundation of the Nile_, as it was rendred by Monsieur _de la Chambre_:
_This_ is to give you another, not only of the _Inundation_, but also of
the _Origine_ of that, and of _other Rivers_, as it is delivered by
Monsieur _Isaac Vossius_, who undertakes in this Book to shew;
1. That those _Subterraneous Channels_, through which several
_Philosophers_ teach, that the Sea discharges it self into the Rivers, are
not only imaginary, but useless, in regard 'tis impossible for the water to
rise from the Subterraneous places up to the Mountains, where commonly the
Sources of Rivers are.
2. He explicates, why, if a Pipe be put into a Bason full of Water, the
water is seen more raised in the Pipe, than in the Bason, and rises higher
according as the Pipe is narrower; On the contrary, if the same Pipe be put
into a Bason full of Quicksilver, the Quicksilver stayes lower in the Pipe,
than in the Bason. The reason, which he renders hereof, is, That as the
Water sticks easily to all it touches, it is sustain'd by the sides of the
narrow Pipe wherein it is included: And indeed, if the Pipe be quite drawn
out of the Water, the Water doth not all fall out, but so much of it
remains, as the sides of the Pipe could sustaine: Whence it is, that the
Water which is kept up by the Walls of the Tube, weighing no longer upon
that which is in the Bason, is thrust upwards, and keeps it self raised
above its Levell; but the Quicksilver not adhering so easily, as Water, to
Bodies it touches, is not sustained by the sides of the Tube, and so mounts
not above its Levell, but rather descends below it, because the Pipe, which
is streight, hinders the endeavor that is in the _Mercury_ to rise to its
Level. He adds, that this Observation makes nothing for the Explication of
the _Origine of Rivers_; because, though it be true, that the Water {305}
by this means rises above its Levell, yet it does never run out at the top
of the Pipe. Having said this, he answers to the other Arguments, commonly
alledged to maintain this Opinion.
3. He pretends, that all Rivers proceed from a _Colluvies_ or _Rendevous_
of Rain-waters, and that, as the Water, that falls upon _Hills_, gathers
more easily together, than that which falls in _Plaines_, therefore it is,
that Rivers ordinarily take their Source from _Hills_. Thence also comes it
(saies he) that there are more _Rivers_, than _Torrents_, in the _Temperate
Zones_; and, on the contrary, more _Torrents_, than _Rivers_, in the
_Torrid Zone_: For, as in hot Climats the Mountains are far higher, the
Water, that descends from them with impetuosity, runs away in a little
while, and formes such Collections of Water, as soon dry up, but in cold
Climats, the Waters do not run away but slowly, and are renew'd and
recruited by Rain, before they are quite dryed up; because the Hills are
there lower, and so the Bed of Rivers hath lesse declivity.
Having thus discoursed of _Rivers_ in _General_, he treats of the _Nile_ in
_particular_; and there
1. Observes, That the Order of the Seasons of the Year is quite inverted
under the _Torrid Zone_. For, whereas it should be then Summer, when the
Sun is near; and Winter, when the Sun is farther off: Under the _Torrid
Zone_ 'tis never lesse hot, than when the Sun is nearest; nor more hot,
than when the Sun is farthest off: So that to the people that live between
the _AEquinoctial_ and the _Tropicks_, Summer begins about _Christmass_, and
their Winter, about St. _Johns_ day. The reason whereof is, (_saith he_)
that when the Sun is directly over their Heads, it raises abundance of
vapors, and draws them so high, that they are presently converted into
Water by the coldnesse of the Air; whence it comes to passe, that then it
rains continually, which does refresh the Air; but when the Sun is farther
off, there falls no more rain, and so the Heat becomes insupportable.
2. He proves by many recent Relations, that the _Sources_ of the _Nile_ are
on this side of the _AEquinoctial_ in _AEthiopia_, of which he gives a very
accurate _Mappe_, correcting many faults which _Geographers_ are wont to
commit in the Description of the Kingdom of the _Abyssins_, which they
believe to be much greater than indeed it is. {306}
3. This supposed, he easily gives an account, why the _Nile_ yearly
overflows about the end of _June_: For, as at that time there falls much
rain in _AEthiopia_, it must needs be, that the _Nile_, whose source is in
that Country, should then overflow, when those rains begin, and subside,
when they cease.
There are besides, in this Book, two other _Tracts_. In the _first_, M.
_Vossins_ endeavours to maintain the Doctrine, he had deliver'd in his Book
_De Lumine_, and to shew, that the _Soul_ of Animals is nothing but _Fire_,
that there are no invisible Atoms; nor so much as any Pores, even in the
Skin of man. Here he treats also of _Refractions_, and alledges the
Examples of several persons, who have then seen the Sun by the means of
Refraction, when really He was under the _Horizon_.
In the _second_, He discourses of some points of the _Mechanicks_; and
relates among other things, that the _Arrows_ and _battering Rams (Aries)_
of the Antients did as much execution, as our _Muskets_ and _Canons_; and
then, that the Vehemence of the percussion depends as much upon the Length
of the percutient Body, as upon the velocity of the Motion. He adds, that
the Length of a Canon ought not to exceed 13 foot, and that a greater
length is not onely useless, but hinders also the effect of the Gun, not
because the Bullet is thrown out of the Gun, before all the powder is fired
(as some believe;) but because the Bullet is then beaten back into the Gun
by the Air, re-entring into it with impetuosity, when the flame is extinct.