_Supposing an homogeneous sphere_ OABCD (Fig. 1.) _revolving uniformly
about its centre, to be acted on at the extremity_ A _of the radius_
OA, _in a direction_ AL _perpendicular to the plane of the equator_
ABCD, _and parallel to the axis of rotation_ Pp, _by a given force,
tending to generate a new motion of rotation at right angles to the
former; It is proposed to determine the change, that will arise in the
direction of the rotation in consequence of the said force._
[Illustration: FIG. 1.]
Let _F_ denote the given force, whereby the motion about the axis P_p_
is disturbed, supposing _f_ to represent the centrifugal force of a
small particle of matter in the circumference of the equator, arising
from the sphere’s rotation; and let the whole number of such particles,
or the content of the sphere, be denoted by _c_: let also the momentum
of rotation of the whole sphere, or of all the particles, be supposed,
in proportion to the momentum of an equal number of particles,
revolving at the distance OA of the remotest point A, as _n_ is to
_unity_.
It is well known, that the centripetal force, whereby any body is
made to revolve in the circumference of a circle, is such, as is
sufficient to generate all the motion in the body, in a time equal
to _that_, wherein the body describes an arch of the circumference,
equal in length to the radius. Therefore, if we here take the arch AR
= OA, and assume _m_ to express the time, in which that arch would
be uniformly described by the point A, the _motion_ of a particle of
matter at A (whose central force is represented by _f_) will be equal
to _that_, which might be uniformly generated by the force _f_, in
the time _m_; and the motion of as many particles (revolving, all, at
the same distance) as are expressed by _cn_ (which, by hypothesis,
is equal to the momentum of the whole body), will, consequently, be
equal to the momentum, that might be generated by the force _f_ ×
_cn_, in the same time _m_. Whence it appears, that the momentum of
the whole body about its axe P_p_ is in proportion to the momentum
generated in a given particle of time _m’_, by the given force _F_ in
the direction AL, as _ncf_ × _m_ is to _F_ × _m’_, or, as _unity_ to
(_F_/_ncf_) × (_m’_/_m_) (because the quantities of motion produced by
unequal forces, in unequal times, are in the ratio of the forces and
of the times, conjunctly). Let, therefore, AL be taken in proportion
to AM, as (_F_/_ncf_) × (_m’_/_m_) is to _unity_ (supposing AM to be
a tangent to the circle ABCD in A), and let the parallelogram AMNL be
compleated; drawing also the diagonal AN; then, by the composition of
forces, the angle NAM (whose tangent, to the radius OA, is expressed
by OA × (_F_/_ncf_) × (_m’_/_m_)) will be the change of the direction
of the rotation, at the end of the aforesaid time (_m’_). But, this
angle being exceeding small, the tangent may be taken to represent
the measure of the angle itself; and, if Z be assumed to represent
the arch described by A, in the same time (_m’_) about the center O,
we shall also have (_m’_/_m_) = (Z/AR) = (Z/AO), and consequently OA
× (_F_/_ncf_) x (_m_/_m’_) = Z × (_F_/_ncf_). From whence it appears,
that the angle expressing the change of the direction of the rotation,
during any small particle of time, will be in proportion to the angle
described about the axe of rotation in the same time, as _F_/_ncf_ is
to _unity_. _Q.E.I._
Altho’, in the preceding proposition, the body is supposed to be a
perfect sphere, the solution, nevertheless, holds equally true in every
other species of figures, as is manifest from the investigation. It
is true, indeed, that the value of _n_ will not be the same in these
cases, even supposing those of _c_, _f_ and _F_ to remain unchanged;
except in the spheroid only, where, as well as in the sphere, _n_ will
be = ⅖; the momentum of any spheroid about its axis being 2-5ths of the
momentum of an equal quantity of matter placed in the circumference of
the equator, as is very easy to demonstrate.
But to shew now the use and application of the general proportion here
derived, in determining the regress of the equinoctial points of the
terrestrial spheroid, let AE_a_F (_Fig. 2._) be the equator, and P_p_
the axis of the spheroid: also let HECF represent the plane of the
ecliptic, S the place of the sun, and HAPNH the plane of the sun’s
declination, making right-angles with the plane of the equator AE_a_F:
then, if AK be supposed parallel, and OKM perpendicular, to OS, and
there be assumed _T_ and _t_ to express the respective times of the
annual and diurnal revolutions of the earth, it will appear (from the
_Principia_, B. III. prop. xxv.) that the force, with which a particle
of matter at A tends to recede from the line OM in consequence of the
sun’s attraction, will be expressed by (_3tt_/_TT_) × (AK/OA) × _f_;
_f_ denoting the centrifugal force of the same particle, arising from
the diurnal rotation. Hence, by the resolution of forces, (_3tt_/_TT_)
× (AK/OA) × (OK/OA) × _f_ will be the effect of that particle, in a
direction perpendicular to OA, to turn the earth about its center O.
[Illustration: FIG. 2.]
But it is demonstrated by Sir Isaac Newton, and by other authors, that
the force of all the particles, or of all the matter in the whole
spheroid AP _ap_, to turn _it_ about its center, is equal to ⅕th of
the force of a quantity of matter, placed at A, equal to the excess
of the matter in the whole spheroid above _that_ in the inscribed
sphere, whose axis is P_p_. Now this excess (assuming the ratio of
π to 1, to express _that_ of the area of a circle to the square of
the radius) will be truly represented by (4π/3) × OP × (OA² - OP²);
and, consequently, the force of all the matter in the whole earth, by
(_3tt_/_TT_) × (AK/OA) × (OK/OA) × (4π/15) × OP × (OA²- OP²). Let,
therefore, this quantity be now substituted for _F_, in the general
formula _F_/_ncf_, writing, at the same time, (4π/3) × OA² × OP,
and ⅖, in the place of their equals _c_ and _n_; by which means we
have (here) (_F_/_ncf_) = (_3tt_/_2TT_) × ((OA² - OP²)/OA²) × ((AK ×
OK)/OA²). Put the given quantity (_3tt_/_2TT_) × ((OA² - OP²)/OA²) =
_k_; and let the angle EA_e_ represent the horary alteration of the
position of the terrestrial equator, arising from the force _F_ (here
determined), and let the arch E_e_ be the regress of the equinoctial
point E, corresponding thereto: then, in the triangle EA_e_ (considered
as spherical) it will be sin. _e_ ∶ sin. AE (∷ sin. EA_e_: sin. E_e_) ∷
EA_e_ ∶ E_e_ (= (sin. AE x EA_e_)/sin. E) = _k_ × (sin. AE/sin. E) ×
((AK × OK)/OA²) = _k_ × ((sin. AE × cos. AH × sin. AH)/sin. E). But in
the triangle EHA, right-angled at A (where HA is supposed to represent
the sun’s declination, AE his right ascension, and HE his distance from
the equinoctial point E[207]) we have (_per spherics_)
sin. AE ∶ 1 (rad.) ∷ co-t. E ∶ co-t. AH,
(sin. AH)² ∶ (sin. EH)² ∷ (sin. E)² ∶ 1² (rad.²)
From whence we get, sin. AE × co-t. AH × (sin. AH)² = (sin. EH)² ×
co-t. E × (sin. E)². But co-t. AH × sin. AH = co-s. AH × 1 (rad.), and
co-t. E × sin. E = co-s. E × 1 (rad.): therefore sin. AE × co-s. AH ×
sin. AH = (sin. EH)² × co-s. E × sin. E; and, consequently, _k_ × (sin.
AE × co-s. AH × sin. AH)/sin. E = _k_ × co-s. E × (sin. EH)² (= E_e_).
Let, now, the sun’s longitude EH be denoted by Z (considered as a
flowing quantity); then, (sin. Z)² being = ½-½ co-s. 2 Z, we shall have
_k_ × co-s. E × (sin. EH)² = ½_k_ × co-s. E × 1-co-s. 2 Z. But the
angle described about the axe of rotation P_p_, in the time that the
sun’s longitude is augmented by the particle Ż, will be = (_T/t_) × Ż.
Therefore (by the general proposition) we have, as 1: ½_k_ × co-s. E ×
1-co-s. 2 Z ∷ (_T/t_) × Ż : ½_k_ × (_T/t_) × co-s. E × Ż - Ż co-s. 2 Z,
the true regress of the equinoctial point E, during that time: whose
fluent, ½_k_ × (_T_/_t_) × co-s. E × (Z- ½ sin. 2 Z), will consequently
be the total regress of the point E, in the time that the sun, by
his apparent motion, describes the arch HE or Z; which, on the sun’s
arrival at the solstice, becomes barely = ½_k_ × (_T_/_t_) × co-s. E ×
an arch of 90°: the quadruple whereof, or ½_k_ × (_T_/_t_) × co-s. E ×
360° (= (3_t_/4_T_) × ((OA²-OP²)/OA²) × co-s. E × 360°) is therefore
the whole annual precession of the equinox caused by the sun. This, in
numbers (taking OP/OA = 229/230) comes out (3/(4 × 366¼)) × (2/230½) ×
0.917176 × 360° = 21´´ 6´´´.
The very ingenious M. Silvabelle, in his essay on this subject,
inserted in the 48th volume of the Philosophical Transactions, makes
the quantity of the annual precession of the equinox, caused by the
sun, to be the half, only, of what is here determined. But this
gentleman appears to have fallen into a twofold mistake. First, in
finding the _momenta of rotation_ of the terrestrial spheroid, and of
a very slender ring, at the equator thereof; which _momenta_ he refers
to an axis perpendicular to the plane of the sun’s declination, instead
of the proper axe of rotation, standing at right angles to the plane of
the equator. The difference, indeed, arising from thence, with respect
to the spheroid (by reason of its near approach to a sphere) will be
inconsiderable; but, in the ring, the case will be quite otherwise; the
equinoctial points thereof being made to recede just twice as fast as
they ought to do. This may seem the more strange, if regard be had to
the conclusions, relating to the nodes of a satellite, derived from
this very assumption. But, that these conclusions are true, is owing
to a second, or subsequent mistake, at Art. 27; where the measure of
the sun’s force is taken the half, only, of the true value; by means
whereof the motion of the equinoctial points of the ring is reduced to
its proper quantity, and the motion of the equinoctial points of the
terrestrial spheroid, to the half of what it ought to be.
That expert geometrician M. Cha. Walmsley, in his Essay on the
Precession of the Equinox, printed in the last volume of the
Philosophical Transactions, has judiciously avoided all mistakes of
this last kind, respecting the sun’s force, by pursuing the method,
pointed out by Sir Isaac Newton; but, in determining the effect of that
force, has fallen into others, not less considerable than those above
adverted to.
In his third Lemma, the momentum of the whole Earth, about its
diameter, is computed on a supposition, that the momentum or force of
each particle is proportional to its distance from the axis of motion,
or barely as the quantity of motion in such particle, considered
abstractedly. No regard is, therefore, had to the lengths of the
unequal levers, whereby the particles are supposed to receive and
communicate their motion: which, without doubt, ought to have been
included in the consideration.
In his first proposition, he determines, in a very ingenious and
concise manner, the true annual motion of the nodes of a ring (or of
a single satellite) at the earth’s equator, revolving with the earth
itself, about its center, in the time of one siderial day. This motion
he finds to be = (3co-s. 23° 29´/4 rad.) × (⅟366¼) × 360°. Then, in
order to infer from thence, the motion of the equinoctial points of the
earth itself, he, first, diminishes that quantity, in the ratio of 2
to 5: Because (as is demonstrated by Sir Isaac Newton in his 2d Lemma)
the whole force of all the particles situated without the surface of a
sphere, inscribed in the spheroid, to turn the body about its center,
will be only 2-5ths of the force of an equal number of particles
uniformly disposed round the whole circumference of the equator, in
the fashion of a ring. The quantity ((3co-s. 23° 29´/4 rad.) × ⅖ ×
(⅟366¼) × 360°) thus arising, will, therefore, express the true motion
of the equinoctial points of a ring, equal in quantity of matter to the
excess of the whole earth above the inscribed sphere, when the force
whereby the ring tends to turn about its diameter is supposed equal
to the force whereby the earth itself tends to turn about the same
diameter, in consequence of the sun’s attraction. Thus far our author
agrees with Sir Isaac Newton; but, in deriving from hence the motion
of the equinoctial points of the earth itself, he differs from him;
and, in the corollary to his third Lemma, assigns the reasons, why he
thinks Sir Isaac Newton, in this particular, has _wandered a little
from the truth_. Instead of diminishing the quantity above exhibited
(as Sir Isaac has done) in the ratio of all the motion in the ring to
the motion in the whole earth, he diminishes it in the ratio of the
motion of all the matter above the surface of the inscribed sphere to
the motion of the whole earth: which matter, tho’ equal to that of the
ring, has nevertheless a different momentum, arising from the different
situation of the particles in respect to the axis of motion.
But since the aforesaid quantity, from whence the motion of the earth’s
equinox is derived, as well by this gentleman, as by Sir Isaac Newton,
expresses truly the annual regress of the equinoctial points of the
ring (and not of the hollow figure formed by the said matter, which
is greater, in the ratio of 5 to 4) it seems, at least, as reasonable
to suppose, that the said quantity, to obtain from thence the true
regress of the equinoctial points of the earth, ought to be diminished
in the former of the two ratios above specified, as that it should be
diminished in the latter. But, indeed, both these ways are defective,
even supposing the momenta to have been truly computed; the ratio,
that ought to be used here, being that of the momenta of the ring and
earth about the proper axe of rotation of the two figures, standing
at right-angles to the plane of the ring and of the equator. Now this
ratio, by a very easy computation, is found to be as 230²-229² to ⅖ of
230²; whence the quantity sought comes out = (3co-s. 23° 29´/4 rad.)
× (⅟366¼) × (230²-229²)/230² × 360° = 21´´ 6´´´: which is the same that
we before found it to be, and the double of what this author makes it.
What has been said hitherto, relates to that part of the motion
only, arising from the force of the sun. It will be but justice to
observe here, that the effect of the moon, and the inequalities
depending on the position of her nodes, are truly assigned by both
the gentlemen above-named; the ratio of the diameters of the earth,
and the density of the moon being so assumed, as to give the maxima of
those inequalities, such as the observations require: in consequence
whereof, and from the law of the increase and decrease (which is
rightly determined by theory, tho’ the absolute quantity is not) a true
solution, in every other circumstance, is obtained.
The freedom, with which I have expressed myself, and the liberty I have
here taken, to animadvert on the works of men, who, in many places,
have given incontestible proofs of skill and genius, may, I fear, stand
in need of some apology. ’Tis possible I may be thought too peremptory.
Indeed, I might have delivered my sentiments with more caution and
address: but, had not I imagined myself quite clear in what has been
advanced, from a multitude of concurrent reasons, I should have thought
it too great a presumption to have said any thing at all here, on this
subject. The great regard I have for this Society, of which I have the
honour to be a member, will, I hope, be considered as the motive for my
having attempted to rectify some oversights, that have occurred in the
works of this learned body.
LIV. _Remarks upon the Heat of the Air in_ July 1757. _in an Extract
of a Letter from_ John Huxham, _M.D. F.R.S. to_ William Watson, _M.D.
F.R.S. dated at_ Plymouth _19th of that Month. With additional Remarks
by Dr._ Watson.
[Read Dec. 22, 1757.]
“FROM the beginning of June last we have had a very dry season,
generally very warm, and sometimes excessively hot. From the 7th to the
14th of this month the heat was violent; greater, indeed, than has been
known here in the memory of man. I have talked with several persons,
who have lived a considerable time in Jamaica, Gibraltar, and Minorca;
and they severally assert, that they never felt such intense heat in
any of those places. Upon the 11th, 12th, and 13th of this month,
Fahrenheit’s thermometer, in the shade, about three o’clock in the
afternoon, was at 87; nay, upon the 12th it was even above 88.
Abundance of people have suffered very severely from these excessive
heats: putrid, bilious, petechial, nervous fevers, are exceedingly
common every-where. Dysenteries, hæmorrhages, most profuse sweats,
affect not only those in fevers, but a vast many others. The days and
nights were so intolerably hot, that little or no sleep was to be
gotten day or night. The wind we had, like the Campsin, actually blew
hot, tho’ strong.
Upon the 15th, about seven at night, at Falmouth, Penryn, Truro, and
thereabouts, a pretty smart shock of an earthquake was felt, attended
with a hollow rumbling noise, throwing down pewter, china-ware, and
such-like. The tinners felt it eighty fathom under ground. No great
damage however was done. The day before we had, about eleven o’clock
before noon, a most violent hurricane, which lasted five or six
minutes, attended with a heavy shower.”
Thus far Dr. Huxham.
The heat of the air at London, during the period above-mentioned, was
much greater than has been usually observed in these high latitudes;
tho’ it was never quite so severe here as at Plymouth. The following
table exhibits the degrees of the heat, taken here upon the respective
days, about four o’clock in the afternoon, by a Fahrenheit’s
thermometer. The instrument was placed in the shade; and the accuracy
of the observer, who favoured me with his minutes, is not to be
questioned.
1757. July 5 75
6 78
7 75½
8 78
10 80¼
11 83¼
12 80¼
13 80
14 85
15 81
16 73
From hence it appears, that the air at London was, upon several
days, hotter than it had been observed at Madeira for ten years
together: for, by Dr. Thomas Heberden’s observations, mentioned in the
Philosophical Transactions, the heat of the air at Madeira, during that
period, was never but once at 80.
William Watson.
LV. _Remarks upon the Letter of Mr._ John Ellis, _F.R.S. to_ Philip
Carteret Webb, _Esq; F.R.S. printed in the_ Philosophical Transactions,
_Vol._ xlix. _Part_ ii. _p._ 806. _By Mr._ Philip Miller, _F.R.S._
[Read Dec. 15, 1757.]
THE paper of mine, which was read before the Royal Society on the
8th of May 1755, and afterward printed in the xlixth volume of the
Philosophical Transactions[208], was written at the request of Mr.
Watson; who informed me, that a letter from the Abbé Mazeas to the
reverend Dr. Hales had been communicated to the Royal Society, in
which it was mentioned, that the Abbé Sauvages had made a discovery of
the juice of the Carolina Toxicodendron staining linen of a permanent
black. But Mr. Watson said, that the letter, he thought, required a
careful perusal before it was printed; and he wished I would confirm
it. I told him, if the letter was put into my hands, I would look it
over, and deliver my opinion of it.
Accordingly Dr. Birch delivered the letter to me; and, upon reading it,
I found, that tho’ this might be a discovery to those two gentlemen;
yet, as it had been mentioned in several printed books long before, I
thought it might not be for the reputation of the Royal Society to have
it printed as such in their Transactions.
This was my motive for writing that paper: in which I have not
endeavoured to depreciate the discovery of the Abbé Sauvages, but
have only mentioned what had occurred to me in those books of botany,
where that shrub is taken notice of. And as the knowlege of it, and
the method of collecting the varnish, might be of service to the
inhabitants of the British colonies in America, I took the liberty of
adding the account given of it by Dr. Kœmpfer.
Mr. Ellis, in his letter to Mr. Webb, asserts, that the American
_Toxicodendron_ is not the same with Kœmpfer’s _Arbor vernicifera
legitima_. This assertion of his makes it necessary to lay before
the Society the authorities, upon which I have grounded my belief,
that they are the same. But it may not be amiss first to take notice,
that the shrub mentioned by the Abbé Sauvages is the same with that,
which the gardeners about London call the Poison-ash. The title of it,
mentioned by the Abbé Sauvages, was given by myself to that shrub, in
a catalogue of trees and shrubs, which was printed in the year 1730;
before which it had no generical title applied to it. And about the
same time I sent several of the plants to Paris and Holland with that
title, which I had raised a few years before from seeds, which were
sent by Mr. Catesby from Carolina.
And altho’ this shrub had not been reduced to any genus before, yet it
had been some years growing in the gardens of the Bishop of London at
Fulham, at Mr. Reynardson’s at Hillenden, Mr. Darby’s at Hoxton, and in
the Chelsea garden, which were raised from seeds sent by Mr. Banister
from Virginia; two of which were growing at Chelsea in the year 1722,
when the care of that Garden was intrusted to me.
The first intimation I had of the American shrub being the same with
Dr. Kœmpfer’s true varnish-tree, was from the late Dr. William Sherard,
in the year 1726, when that gentleman desired me to bring him a
specimen of the American Toxicodendron from the Chelsea garden; which
I accordingly did: and then the Doctor, and Dr. Dillenius, compared
it with a dried specimen in the collection of the former, which was
gathered in Japan, and which, if I remember right, he told me he
received from Dr. Kœmpfer some years before. It appeared to those two
gentlemen, that they were the same; and their skill in the science of
botany was never doubted.
About a year after this, I carried a specimen of the American
Toxicodendron to an annual meeting of some botanists at Sir Hans
Sloane’s in Bloomsbury; where there were present Mr. Dale of Braintree,
Mr. Joseph Miller, Mr. Rand, and some others; which was then compared
with Dr. Kœmpfer’s specimen, whose collection Sir Hans Sloane had
purchased: and it was the opinion of every one present, that they were
the same. Nor has any one doubted of their being so, who has compared
the American shrub with Kœmpfer’s figure and description of his true
varnish-tree, but Mr. Ellis.
And now give me leave to examine his reasons for differing in opinion
from every late botanist, who has mentioned this shrub.
He says, that the midrib, which supports the lobe leaves, is quite
smooth in the poison-ash, as is also the under side of the leaves;
whereas Dr. Kœmpfer, in his description of the midrib of the true
varnish-tree, calls it _læviter lanuginoso_; and in his description
of the lobes or _pinnæ_ he says, they are _basi inequaliter rotunda_;
whereas those of the poison-ash come to a point at their footstalks
nearly equal to that at the top. These characters, Mr. Ellis thinks,
are sufficient to prove, that they are different plants: and he blames
Dr. Dillenius for having omitted these necessary characters in his
description of it; and supposes this must have misled the accurate
Linnæus, who quotes his synonyma.
But as Dr. Linnæus is possessed of Kœmpfer’s book, he would little have
deserved the appellation of accurate in this particular, had he not
consulted the original, but trusted to a copy. But this I know he has
done, and is as well assured, that the plants in question are the same,
as Mr. Ellis can be of the contrary.
But here I must observe, that the branch, from which Dr. Kœmpfer’s
figure is taken, is produced from the lower part of a stem, which seems
to have been cut down, and not from a flowering branch; and it is not
improbable, that his description may have been taken from the same
branch: and if this be the case, it is easy to account for the minute
differences mentioned by Mr. Ellis; for it would not be difficult to
produce instances of hundreds of different trees and shrubs, whose
lower and upper branches differ much more in the particulars mentioned
by Mr. Ellis, than the figure and description given by Kœmpfer do
from the American Toxicodendron. I will only mention two of the
most obvious: the first is the white poplar, whose shoots from the
lower part of the stem, and the suckers from the root, are garnished
with leaves very different in form and size from those on the upper
branches, and are covered on both sides in the spring with a woolly
down. The next is the willow with smooth leaves, which, if a standard,
and the head lopped off, as is usual, the young shoots are garnished
with leaves much broader, and of different forms from those on the
older branches; and these have frequently a hairy down on their under
surface, which does not appear on those of the older. So that a person
unacquainted with these differences in the same tree would suppose they
were different. And the American Toxicodendron has varied in these
particulars much more, in different seasons, than what Mr. Ellis has
mentioned.
Mr. Ellis next says, that the Toxicodendron mentioned by Mr. Catesby,
in his Natural History of Carolina, is not the same with that, which
is now called by the gardeners poison-ash: but I am very positive of
the contrary; for most of the plants in the nursery-gardens about
London were first raised from the seeds, which were sent by Mr. Catesby
from Carolina; part of which were sent to the late Dr. Sherard, as
is mentioned by him in the Philosophical Transactions, Nº. 367; and
another part came to my hands, from which I raised a great many of the
plants, which were distributed, and some of them are now growing in the
Chelsea garden.
And that this shrub grows naturally in Carolina, I can have no doubt,
having received the seeds of it two or three times from the late Dr.
Dale, who gathered them in the woods of that country.
In my paper above-mentioned I likewise observed, that the seeds, which
were sent to the Royal Society by Father D’Incarville, for those of
the true varnish-tree, did not prove to be so; but the plants, which
were raised from them, were taken to be referred to the spurious
varnish-tree of Kœmpfer; which I believed to be the same, and own, that
it is yet my opinion, notwithstanding what Mr. Ellis has said to the
contrary: for the number of lobes or _pinnæ_ on each leaf, with their
manner of arrangement on the midrib, are the same. And here we must
observe, that the figure of this given by Kœmpfer is from a flowering
branch; and every gardener or botanist must know, that the leaves,
which are situated immediately below the flowers of most winged-leaved
plants, have fewer lobes or _pinnæ_, than those on the lower branches:
therefore I must suppose it to be the case in this plant; and from
thence, with some other observations which I made on the seeds, I have
asserted it to be the wild or spurious varnish-tree of Kœmpfer. But Mr.
Ellis is of a contrary opinion, because the base of the lobes of those
plants, which were raised from Father D’Incarville’s seeds, are rounded
and indented like two ears. In Dr. Kœmpfer’s figure and description of
the _fasi-no-ki_, the leaves are intire, and come to a point at their
base.
Here I think Mr. Ellis is a little too hasty in giving his opinion,
as he has not seen this plant in the state, that the branch was, from
which Kœmpfer’s figure was taken. For as there are often such apparent
differences between the leaves on the lower branches of trees, and
those which are at their extremities, as that in the descriptive
titles of the species Dr. Linnæus frequently uses them to distinguish
one from another; so in making the same allowance for the plant in
question, I cannot help thinking that I am in the right, and must abide
by my opinion, till the plants, which have been raised from Father
D’Incarville’s seeds, have flowered, to convince me of the contrary.
However, I cannot help observing, that Mr. Ellis has given a title
to this shrub before he had seen any of the characters, which are
necessary to determine the genus. And I have pretty good reason to
believe it should not be joined to the Rhus; for the three seeds,
which I received from the Royal Society, were shaped like a wedge,
being thicker on one edge than the other, and not unlike those of the
beech-tree, as I noted in my catalogue when I sowed them; and, by their
structure, seemed as if the three seeds had been inclosed in the same
capsule.
If it proves so, this will by no means agree with the characters of
Rhus; especially if the male flowers should grow upon different plants
from the fruit, which is what I suspect. Nor can I agree with Dr.
Linnæus in this particular of joining all the species of Toxicodendron
to the genus of Rhus, many of which have their male flowers growing
upon different plants from the fruit; and therefore would more
properly come into his twenty-second class of _Dioecia_, than his fifth
of _Pentandria_, into which he ranges the Rhus. At the bottom of the
characters of that genus he has added a note, to shew the varnish-tree
is so.
But as there are several other species which agree in this essential
character of distinction; so, according to the Linnæan system, they
should be separated from the Rhus, with another generical title.
Mr. Ellis observes, upon the poetical description, which he lays
Kœmpfer has given of the leaves of the wild varnish-tree turning red in
the autumn, that he had not found it to be the case of the tree growing
in the stove at Busbridge. How it appeared in that situation, I know
not; but the leaves of all those, which are growing in the Chelsea
garden, and stand in the open air, do constantly change to a purple
colour in the autumn, before they fall off from the shrub: but those
of the true varnish-tree are much more remarkable for the deepness of
their colour.
Mr. Ellis says, he had received a letter from Dr. Sibthorp, professor
of botany at Oxford, in which the Doctor informs him, that there is
no specimen of the true varnish-tree in the Sherardian collection at
Oxford; but that there is one of _fasi-no-ki_, or spurious varnish-tree
of Kœmpfer. How the Doctor could write so, I cannot conceive; for I am
very sure there was no specimen of the latter in that collection while
it remained in London, having myself often viewed that part of it:
and sure I am, Dr. Dillenius never added that synonym to the former:
and I do believe the latter was no other way known in Europe, than by
Kœmpfer’s figure and description of it, excepting that specimen of
Kœmpfer’s now in the British Museum.
But, to confirm what I have before said, of Dr. Sherard’s having a
specimen of the true varnish-tree, I beg leave to quote what Dr.
Dillenius has written in the _Hortus Elthamensis_; where, after
having described the American Toxicodendron, he says, _Ceterum
historiam verniciferæ arboris Japoniæ, diligenter et accurate more suo
exsequutus est laudatus Kœmpferius, cujus et descriptio et figura,
quin et planta sicca, quæ in Japonia lecta servatur in phytophylacio
Sherardino, nostræ huic speciei examussim quadrat: id tantum, sexus
nempe differentia, prætervisa fuit auctori: quoniam autem ille liber
non in omnium his in locis, multo minus in America, manibus versatur,
non alienum videtur, si qui, quorum interest, hæc legerint, ut norint,
quæ ille de collectione & preparatione vernicis illius habet, hoc loco
transcribere._ Then he goes on transcribing from Kœmpfer the manner, in
which it is collected.
After this, I find Mr. Ellis is inclinable to think, that the
poison-ash, as it is called by the gardeners, is the same with the
_fasi-no-ki_, or spurious varnish-tree of Kœmpfer. The difference
between these shrubs does not consist in small and minute particulars,
but the most obvious striking marks of distinction appear at first
sight; for the poison-ash has rarely more than three or four pair of
lobes to each leaf, terminated by an odd one: in which particular it
agrees with the true varnish-tree of Kœmpfer; whereas in the figure,
which Kœmpfer has given of the spurious varnish-tree, the leaves have
seven or eight pair of lobes terminated by an odd one: and this
figure, as I before observed, is drawn from a flowering branch. Every
one, who is the least acquainted with these things, knows, that the
leaves immediately below the flowers are considerably less than those
on the lower part of the branches: therefore this is a more essential
note of distinction than those mentioned by Mr. Ellis.
I must also observe, that Mr. Ellis would suggest, that I supposed
these two shrubs were only varieties of each other produced by culture:
whereas it must appear to every one, who reads my paper, that my
intention in mentioning the spurious varnish-tree was to shew it was
different from Kœmpfer’s true varnish-tree, altho’ Kœmpfer supposes
otherwise.
For the satisfaction of the curious, I have added a leaf of each shrub,
which are now growing in the Chelsea garden, that if any person has the
curiosity, they may compare them with Kœmpfer’s.
In my paper I took notice, that one of the best kinds of varnish was
collected from the Anacardium in Japan; and recommended it to the
inhabitants of the British islands in America, to make trial of the
occidental Anacardium, or Cashew-nut tree, which abounds in those
islands. This has occasioned Mr. Ellis to take great pains to shew,
that the eastern and western Anacardium were different trees: a fact,
which was well known to every botanist before; and of which I could not
be ignorant, having been possessed of both sorts near thirty years.
But as I was assured, from many repeated experiments, that the milky
juice, with which every part of the Cashew-tree abounds, would stain
linen with as permanent a black as that of the oriental Anacardium; so
I just hinted, that it was worth the trial. Nor was my hint grounded
on those experiments only, but on the informations I had received
from persons of the best credit, who had resided long in the American
islands, that people are very careful to keep their linen at a distance
from those trees, well knowing, that if a drop of the juice fell upon
it, they could never wash out the stain.
But Mr. Ellis, in order to prove that this tree has no such quality
of staining, says, he has made some experiments on the caustic oil,
with which the shell or cover of the Cashew-nut abounds; and that he
found it was not endued with any staining quality. But surely those
experiments cannot be mentioned to prove, that the milky juice of the
tree has not this property: and Sir Hans Sloane, in his History of
Jamaica, says, that the inhabitants of Jamaica stain their cottons with
the bark of the Cashew-tree.
I shall not intrude farther on the patience of the gentlemen, who may
be present when this paper is read; but humbly crave their pardon for
detaining them so long: nor should I have given them this trouble, had
not I thought my reputation concerned on the occasion.