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A great many fuch inftances might be added, if I thought it worth while, or, that any one would fearch after me to fee whether things are fo or not. But I fhall content myself with obferving, in the general, that Mr Johnson has unitated the Socinians in indulging a trifling criticism with the holy feriptures and the writings of the fathers, which plays upon words, and hunts after all poffible fignifications in order to find out a meaning that may be agreeable to his darling hypothefis, which he was obilinately refolved to defend, or, in the words of Origen, which he wrefted and mifapplied to his bread-facrifice, to hold falt as long as he lived. But he did not know the fcriptures, nor understand his own church-catechism.

SIR,

September 10th, 1744. If the following obfervations, &c. will not take up too much room in your Magazine, you will by inferting them therein oblige (among others) your conftant reader,

And bumble fervant,

EXONIENSIS.

Obfervations on Mr Smith's Hypothefis concerning the Tails of Comets.

T

HIS author in p. 42 of his late Treatise of Comets, printed for 7. Robinson, endeavours to account for the fingular position of their tails, regarding unexceptionably one quarter, by fuppofing that phænomenon to be occafioned by the lucid vapours (with which the atmospheres of comets abound) becoming visible to us only in the comic and penumbral fhadow of the comet: That this is not the fole caufe (at least) of fuch an appearance, will, I prefume, evidently appear from what follows. For,

1. If it were fo, the tail would always appcar, cæteris paribus, longest when the comet is at the greateft diftance from the fun, and fhortest when rear him, which is contrary to experience.

2. The tail would appear exactly of the fame fize at the fame distance from the fun, whether in the comet's defcent or afcent: but it has been obferv'd that comets in their afcent from the fun have much larger and longer tails than when at the fame diflances from him in their decent.

If it be faid that this is occafioned by the luminous vapors becoming more vifible after the perihelion, on account of the greater quantity of them emitted from the comet when it has required fuch an intense heat as it muft then have; I anfwer, tho' this may cause the tail to appear bigger, by increafing the fplendor of the penumbra, it cannot make it appear of a greater length; for how high foever thefe vapours may afcend from the nucleus of the comet, they will, according to our author's hypothefis, be only visible in the conic and penumbral fhadow, all their other parts being loft and extinguifhed in the fuperior luftre of the fun.

3. If this hypothefis were true, the tails of comets would never deviate in the lealt from their oppofition to the fun, but the vertex of the cone would always be as directly oppofite to him as thofe parts thereof

which

Mr Smith's hypothefis of tails of comets examin'd. 231

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which are nearest the nucleus: but on the contrary it has been observed in feveral comers, and particularly in the laft, that the upper part of the tail inclined towards the parts which the comet had left by its motion. Mr S. to remove this difficulty, would have it that the tail appeared fenfibly bent only when the comet approach'd the horizon, which, he says, was occafioned entirely by the refraction of the air, by which the comet's body appeared to be elevated above the horizon, when it was actually fet, and the different parts of its tail, according to their elevation, undergoing different degrees of refraction bent it into the form of a curve, fuch as it feem'd to be.'To this it may be answer'd, that the tail of the late comet appeared (almoft if not quite) as much bent when the comet was 10 or 15 degrees above the horizon, as when it was juft fetting: but fuppofing it true that it appear'd fo only when near the horizon, yet even in this cafe I can't conceive that it could acquire any apparent curvature by the laws of refraction, but that it would only make a fomewhat more oblique angle with the horizon, and appear a very little fhorter than when farther above it, and this variation of its apparent from its real pofition is fo trifling, that 'tis fcarce worth our notice. For fuppofing the comet to be actually on the horizon, its tail extending 20°. in length, and making fuch an angle with the horizon, as that the altitude of the upper part of the tail fhould be but 14°. and confequently the middle part thereof about 7°. or 7°. 30'; then the comet itself, according to Tycho's table, would appear but 30' above the horizon, the middle of the tail 8'15" above its real altitude, and the upper part thereof but 8' 30", and nearly proportionable in the intermediate parts thereof: If this be duly confidered, it will from hence plainly appcar that if there fhould be any curvature by means of the refraction, it would be altogether imperceptible, not fenfibly varying from a ftraight line. I have here fuppos'd the tail to make an oblique angle with the horizon, because, if it made a right angle therewith, is beyond all difpute that the refraction could not then occafion any apparent curvature.

I am aware that this bent of the tail inay be plaufibly (tho' not fatiffactorily) accounted for on our author's hypothefis, by fuppofing the upper parts thereof generally at a greater diftance from the earth, than thole parts which are contiguous to the nucleus; for it being now pait difpute that the motion of light is fucceffive and not inftantanecus, the rays coming from the luminous vapours in the upper part of the tail require longer time to reach the eye of the obferver than those which come from the parts of the tail neareft the comet, and confequently the comet and parts of the tail contiguous thereto, must appear fomewhat farther on in their courfe than the upper parts of the tail, which will therefore seem to incline, or bend backwards. I confefs, were the above objection concerning the curvature of the tail, the only one that could be made to his hypothefis, I fhould not think it much weakened thereby, but that (confidering the progreffive motion of light) the great distance of the upper part of the tail might probably be the caufe of fuch an appearance but if the tails of comets be really fo vaftly extended as that the distances of their upper parts mcafured from the earth, exceed the distances of the comets themfelves and the lower parts of their tails, fo very much, as to make them appear to remarkably bent; I fay, it this be really the cafe, (which will admit of fome doubt, and be liable to the fame

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kind of objections as the arguments deduced from the refraction of light) it will as well account for (or at least help to confirm) Sir Ifaac Newton's hypothefis, who thinks the appearance of the tails owing to fteams and vapours exhal'd from the body, and grofs atmosphere of comets, and afcending perpendicularly; but afligns a different caufe for this curvature, viz. the fame that causes the fmoke of a burning coal in motion to ascend obliquely, inclining from the motion of the coal. Now why may not this apparent bent of the tails of comets be partly caus'd by the very great ditance of the upper part of their tails from the earth (occafioning the light reflected from thence to be longer in coming down than from the lower parts near the nucleus) tho' chiefly by the motion of the comet, which hinders the perpendicular afcent of the fteams and vapours which compofe the tail? And if both concur to caufe this appearance, the only thing that I apprehend can be faid in favour of Mr Smith's hypothefis, will be as ftrong, if not a ftronger argument in favour of Sir Ifaac Newton's, which having other proofs to confirm it, of which Mr Smith's is deftitute, the former may more fafely be adhered to, at leaft till another lefs liable to exceptions fhall be discovered.

❖❖

Some farther confiderations relating to the Cyclopædia, occafioned by a Plar. and Specimen beretofore proposed; communicated to the editor of the Mifcellaneous Correfpondence.

SIR,

W

THEN I first met with your Magazine for Sept. 1744, and therein viewed the contents of the 3d number of your Miscellaneous Correfpondence, perceiving there was fomething in it refpecting Mr Chambers's Cyclopedia, and the defigned Supplement, I immediately determined to have all the three numbers of the above pamphlet, and gave an order for them accordingly.

The following particulars were laid together, immediately upon confidering what appeared in the aforefaid 3d number of your pamphlet, under the title of Miscellaneous Correfpondence; but thrown by, as I was wilJing to see what remarks might be made by others. With the utmost diligence on my part, I have but juft now obtained a fight of the 4th number, feveral orders being fucceffively given by my bookfeller in the country, before he could have it down. And now, Sir, finding less in your laft Mifcellany relating to the Cyclopedia than I expected, it has put me upon troubling you with my thoughts hereupon, with which you may ufe your pleature.

Time, with your own obfervations and experience will moft fully confirm or confute what I am going to fay;-but I am apt to believe while you have any thing material to propofe and publifh concerning the above great work, either respecting the improvement of what is already done, or any additions thereunto, you will have a fufficient call for your pamphlet, and oblige your readers at the fame time. I fincerely thank you and your ingenious correspondents for what has been made public in the

two

two folio fheets; and it is hoped, both they and others will furnifh you with more, alike deferving of public regard.

I join with the ingenious author of the Plan and Specimen, in a firm belief that the Cyclopædia is the best collection by far of any of the kind; -I join with him also in respects to the worthy proprietors of that weighty work; nor am I lefs fenfible of, or lefs concerned at, the ill attempts which have been made to plunder and pirate this, their lawful property but for the comfort of these proprietors I may fay, they are as yet very fecure, fince the imitations of the Cyclopædia are no lefs abfurd, than the imitators are dishonest.

But though we gratefully remember the deceafed Mr Chambers, and give to his work (already published) its due praise, we must yet acknowledge, with all its excellencies it hath its deficiencies, and will admit of many amendments. Indeed we can never rationally expect a work of this kind fhould be compleat and perfect; but ftill, the nearer perfection is arrived at, the better; and it is pity any reafonable pains or expence fhould be fpared that might conduce hereunto.It is acknowledged a weighty undertaking; but it is yet hoped the proprietors will not fhrink at it, fince they may be affured their work will meet with the readieft reception. May I here with modefty add,-fhould it please his facred majefty king George the fecond to patronize and promote the completiore and publication of this extenfively useful and excellent work, it would be far from being accounted among the least of thofe royal favours, which the king has conferred upon his fubjects:-And if I might be allowed from what I know of myself, to speak for others, this generous aft would happily tend yet farther to endear his majesty to a confiderable part of his fubjects, and fuch a part too as are capable (in fome respects) of ferving his majesty and the prefent royal family, beyond many others.

I fhould greatly rejoice to fee the whole body of the Cyclopedia publifhed agreeable to the propofed Plan, or any improvement of that Plan, fuppofing it be capable of any. As it now ftands, I highly approve of the directions and differences propofed, particularly the numbering the paragraphs at the end,-indenting them (or the reverfe) at the beginning, judicious arrangement of the articles,-the propofed ufe of Italic, with the flender ufe of capitals, &c. In fhort, the Plan feems to me the product of thought, the Specimen is ingenious and judicious,—and the fupplemental articles exceeding good, and are well digefted and drawn up. With this general approbation I could with pleafure take leave of this public-fpirited gentleman and his generous performance ;-but when I confider the thing in view is not of a perfonal or private nature,and that what this writer has publifhed, was done with defign that it should be fcanned and maturely confidered by others;-alfo, that more than a little may depend upon faithfulness and freedom upon this occafion, &r. it is hoped he will not fuppofe any of the following remarks proceed from a fpirit delighting in contradiction, or pleated with oppofition any farther than right, truth, and publick welfare may feem fome way concern ed therein.

There is no queftion but that a part of the beauty and excellency of fuch a work, as a dictionary of arts and fciences is, does confift in the due arrangement of the materials, and placing them under the moft proper heads; (as in the Plan, Par. 6th, with the notes depending :) and befare,

fome

234
fome proper rules adhered to, may be of general ufe to direct the dif-
pofal of the materials throughout the work: but it is a doubt with me,
whether this can ever be done to the full fatisfaction of every reader,
as all are not equal judges, and yet every one will here judge for him-
felf. Perhaps, alfo, this gentleman himself is not quite clear as to this
particular, fince in Par. 7th of his plan, he fays, that accidental points
in perspective, and accidental dignities in aftronomy, ought to have
been confidered under the heads of point and dignity ;---and yet, if I
understand him in Par. 10th, he feems to intimate, that point, as it
relates to astronomy, ought to be explained under aftronomy “; and then,
confequently point in peripective, under perspective, &c. I could with
that this matter might be fuitably attended to; yet I conceive there
is not a great deal depends upon it, fince if the author herein has done
wrong, his references fet me right.

As to the fparing ufe of capitals, and fhorter ways of reference, I like them in the main very well, as taking up lefs room; for I love to fee a good book printed upon a good paper, and the fame well filled; and I am very fure there will need no artful contrivances of any fort, to fwell the work; for, though I would not with that any thing should be admitted into it which might feem heavy and tedious to a judicious reader, nothing but the cream and quinteffence of what has been wrote upon the feveral fubjects by the beft writers ;---yet, of these choice materials there is good ftore, only it will require fome confiderable pains to collect them, unlefs, (as I would hope) it be in good part done already. But palling this, I could almoft petition for the ufe of capitals for a few words more than this gentleman feems willing to allow them to; particularly for the words God, Lord, and Spirit, where this laft does intend the divine fpirit. This I find has been noticed by others: I fhall therefore only obferve,--according to my notion hereof, God, Lord, and Spirit, may be confidered under the clafs of proper names, and upon that footing, confiftent with the gentleman's own fcheme and cuilom, each may lay claim to an initial capital, as well as any other of that clafs.

I like the propofed fpecimen (in the general) extremely well: fuch a marshalling of the materials in their refpective articles would be of fingular fervice to the whole. Almost every difeafe incident to the human beings may be illuftrated under fome or all of the following fubdivifions, diftinguifhed by Italics, viz. Name, Nature, Caufes, Kinds, The gentleman indeed does not fo well apCafes, Prevention, Cure. prove of these logical terms; and it is manifeft from his fpecimen, we do very well without any direct ufe of them; and yet, (for the fake of variety) I think we may not disagreeably make nearer approaches to them. (V. the article ANEURISM b reunto annexed). And as to other articles, (efpecially if any thing large) they may be thrown under certain divifions, fomewhat analogous to thofe before mentioned, according to the nature and matter of the articles themselves.

may

It it certainly beft that each article fhould be confidered together, and not divided among fynonymal words :-ufelefs repetitions are hereby avoided, and the reader has what he wants at one view: But, then, every fynonymal word ought carefully (though barely) to be inferted in its proper place, and each one have a reference annexed to

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