Chapter IX: Part 9

Auctores, qui aquæ dulcis polypos examinarunt, quatuor eorum species enumerant: sed in aqua marina major differentium specierum numerus est; plus quam viginti diversos vidi polypos, quos ut plurimum in laudatis figuris etiam delineavit accuratissimus _Ellis_, et profecto adhuc plures sunt. Sed hic monendum, quod cum aquæ dulcis polypi nudo oculo facile queant conspici, plerique marini non nisi lente aut microscopio possint examinari: et aqua marina, in qua polypi vivunt, bis, vel ad minimum semel, nucthemeri spatio, debet renovari, aut polypi moriantur.

Ad exemplum Dⁱ. _Schaffer_ in duas species primo polypos distinguam; in polypos, qui cellulas sibi construant, et in polypos, qui corporis extremitate corallinis aliisque corporibus extus sese affigant, vel in cavitates naturales alcyoniorum, coralliorum, &c. (de quibus in posterum) irrepant, ut cancelli in vacua buccina. Polypi, qui in cellulis habitant, cæteris plerumque sunt minores: horum cellulæ corallinæ[173] truncum vel ramos circumdant, a quibus prudenti manu sine corallinæ læsione satis facile possunt abradi: et si hæ cellulæ non nimia sint copia, et corallina contra solis splendorem inspiciatur, præsertim si color vivide ruber, aureus aut subniger est, facile per ipsas cellulas translucet.

Polyporum, qui sine cellulis in corporum quorundam cavitatibus habitant, aut extrinsecus illis affixi sunt, plurimæ sunt species. Apertis[174] corallinæ tubulariæ ramis (nam in tali planta semper adsunt rami vel tubi naturaliter[175] clausi, id est, integri, in quibus nunquam polypus insidet) majorum polyporum species sæpius supra sedet; quos a colore rubente polypos vocabo _coccineos_, et præ cæteris observavi. In detritis et apertis, ut modo dixi, corallinæ tubulariæ ramulis, inserta sua cauda vel corporis parte posteriore, polypus habitat, et ex hoc ramo facile et sæpe levi quassatione delabitur, præsertim si ille jam per aliquot dies servatus debilis, æger, aut mortuus sit[176].

Si vegetum talem polypum, corallinæ insidentem, vehementius amplificante microscopio intueris, facile differentiam vides inter scabram et quasi granulatam polypi cutem, et lævissimam corallinæ corticem.

Hic polypus coccineus duplici brachiorum genere est munitus, quod in aliis minoribus non vidi; et hæc coloris sunt subalbidi. [177]Inferiora et longiora octodecim vel viginti sunt, nam numerus sæpe variat, et expansa patinam formant, in cujus medio[178] ipsum polypi corpus coccineum est. Hoc corpus in duas partes dividi potest. Inferiori placentam referenti perpendiculariter alia pyriformis est infixa, quæ duodecim[179] vel quatuordecim habet brachia, prioribus tenuiora et breviora.

Hanc partem pyriformem polypus valde [180]extendere potest, præsertim si prædam captans expansa claudit[181] brachia; et rursus ita contrahere, ut quasi [182]globulus inferiori et depressæ parti adhæreat. In extremo hujus partis [183]os polypi esse videtur: sed ob partium exilitatem non omnia satis distincta possunt videri, ut in majoribus aquæ dulcis polypis; sed ex similitudine partium hæc tuto licet concludere.

Si longiora brachia fortiori microscopio attente contemplaris, cutem eorum valde asperam vides, ut est piscium (quos _Haijen_ vocant) vel ut superficies corii granulati (_chagrein-leer_) forsitan ut minora animalcula, quæ polyporum esca sunt, eo melius, ne elabantur, retinere possint. Sed inter hujus speciei polypos vidi umum cæteris[184] majorem, ex cujus corpore, illo loco ubi pars superior inferiori et depressæ inhæret, sex vel octo enascebantur[185] ramuli, in quorum extremitatibus erant duo vel tres parvi globuli, punctum coccineum in medio habentes. Huic polypo bis in die novam dedi aquam, quam maxime de ejus vita sollicitus, ea spe, ut hi globuli in juniores excrescerent polypos, sed quamvis per mensem sic vivum servaverim, nihil mutatum vidi, nisi quod globuli paululum evaserint majores.

Quæ deinceps de polyporum generatione observavi, non ita mihi satisfaciunt, ut illa pro certis et comprobatis habeam: si vero hac æstate meliora adiscam, Regiæ Societati indicabo.

_De aliis Insectis Marinis._

Si noctu aqua maris, quæ littora nostra alluit, lapide injecto vel baculo movetur, innumeras videre est scintillas igneas, quæ nihil aliud sunt, quam minima animalcula lucentia, non nisi fortiore microscopio visibilia.

Ut hæc animalcula idoneâ colligas copiâ, sufficientem aquæ quantitatem, in qua has scintillas observasti, per chartam emporeticam filtrare facias, donec semiuncia aut minus aquæ supra chartam restat: hujus guttula, vitro concavo, penicilli vel pennæ ope, imposita, fortiore microscopio examinetur, et celerimo motu illa natare videbis. Tres diversas horum observavi species, quas ad vivum delineatas exhibet tabulæ X. fig. I.

Sed mare plura alit insecta, quibus hæc lucendi facultas inest, et quorum in corallinis repertorum quædam delineata sunt tab X. fig. 1, 2, 4, 5. sed quoniam plures [186]auctores de his scripserunt, non commemorabo.

Si corallinæ recenter ex mare extractæ major planta, orbi porcellano concavo, et cujus fundus est profundi coloris cærulei, cum sufficiente quantitate aquæ marinæ pellucidissimæ et filtratæ, at ante jam monui, imponatur, et ejus ramuli prudenter penna expandentur, et lente oculari inspiciantur, silvam saepius videre est, in qua plurima pascuntor animalia, præter diversi generis polypes ramis infixos et brachia extendentes: alia plura sunt, præsertim in infima parte, si corallinæ supra ostrea creverint, quæ huc et illuc cursitant, et forsitan sæpius hianti ostreo alimento inserviunt. Sic vigesimo tertio Octobris 1756 ostreum accepi, cui magna [187]corallinæ planta erat innata, in qua, præter tres diversas polyporum species, sex differentia reperiebam insecta. [188]Primum vermis erat, cujus caput sex majoribus et duobus minoribus cornubus erat instructum. [189]Alteram valde parvum araneam longipedem (Gallis _le Faucheur_) referebat, admodum lente se movens. Tertium vermis erat, similis figuræ 3, sed in designando deperdebatur. [190]Quartum, quintum et sextum non nisi fortiore microscopio distincte erant visibilia. Horum quod littera c nocatur, mirandæ erat structuræ.

Diversa sic ostrea et corallinas explorans, plura talia admiranda insecta vidi, quorum delineationem sistunt tabulae X. figuræ 2, 3, 4, 5, 7. Decimo sexto ejusdem mensis Octobris, plures mihi sed valde parvæ apportabantur corallinæ, quæ a dolio coniformi erant abrasæ: in his licet sæpe et attente exploratis nullos detegere poteram polypos, sed duo alia mirabilissima insecta.

_I. Rhosiud ad vivum pinxit._ _J. Mynde sc._]

Horum, quæ secunda figura tabulæ decimæ littera A exhibet, erant millia, celerrimo motu vel repentia vel natantia: sex suis pedibus postremis ramulum arripiebant, ut erucarum, quas geometras appellant, mos est, et mirum in modum prone et supine se flectentes, de ramo in ramum saliebant quasi agilissimi. Inter hæc erant pauca cæteris majora, quæ [191]naturali et [192]aucta magnitudine delineare curavi. [193]Alterum animal non minos mirum erat; sed horum omnium cognitio multo melius delineationis inspectu, quam ex valde prolixa descriptione peti potest.

Sed si omnia insecta marina, quæ in diversis corallinis reperi, delineare vellem, infinitum opus susciperem; nam eorum numerus et diversitas captum nostrum superant.

Hæc ergo, ut spero, sufficient ad demonstrandum corallinas non polyporum opus aut fabricam esse, sed his et plurimis aliis insectis marinis domicilio et perfugio aut alimento inservire.

Dabam ZirizϾ in Zelandia,
17 Martii 1757.

TABULARUM EXPLICATIO.

TABULA SEPTIMA.

_Fig._ I. Exhibet corallinæ plantam, quæ corallina muscosa, sive muscus marinus tenui capillo spermophorus vocatur.

_Fig._ II. Corallina ramulis dichotomis teneris capillaribus rubentibus. _Fig._ III. Junior planta corallinæ tubulariæ laryngi similis.

_Fig._ IV. Duæ species _a_, _b_, fig. I. et. II. et _c_ eschara papyracea utrinque cellulifera, uni basi adnatæ, quod sæpius in doliis marinis coniformibius contigit.

_Fig._ V. Corallinæ rubræ ramulus, quem per aliquot hebdomadas in aqua marina sæpius renovata servavi, quo tempore parvi ramuli _a_, _a_, multum creverunt, et alii _b_, _b_, pullulaverunt.

_Fig._ VI. Pars conchæ ostrei, in qua, præter filamenta quædam viridia, duo polypi _a_ _a_ conspiciendi.

_Fig._ VII. Cancer arachnoideus, cui duæ polyporum species insidebant. Singulus in _a_, et multi cellulas habitantes in _b_.

_Fig._ VIII. Animal, quod _aarsgat_ vocatur, et januis emissasiorum veterioribus et navibus accrescit: huic parva corallinæ planta erat innata, in qua nullos detegere poteram polypos; plurimos vero _b._ _b._ ipsi animali insidentes.

_N.B._ Caudas horum et præcedentis figuræ polyporum nimis longas delineavit pictor, ut eo melius in conspectum venirent.

TABULA OCTAVA.

_Fig._ I. Ramus corallinæ rubentis magnitudine naturali.

_Fig._ II. Idem microscopio visus, et tres polyporum species in eo conspiciendæ.

_a. b._ Duæ diversæ species caudâ vel corporis parte posteriore corallinæ affixæ.

_c._ Tertia species in cellulis habitans. _d._ Polypus mortuus.

_e._ Polyporum cellulæ.

_Fig._ III. Planta corallinæ tubulariæ laryngi similis magnitudine naturali.

_Fig._ IV. Hujus plantæ ramus maximus, microscopio visus, in quo quinque diversos polypos inveni.

_a._ Prima et maxima species polypi, quem coccineum voco, et tab. IX. fig. II. fortiore adhuc microscopio visum exhibet.

_b._ Eadem sed minor species.

_c._ Tertia, quæ eadem ut hujus tabulæ fig. II. litt. _b_.

_d._ Quarta, quæ eadem ut hujus tabulæ fig. II. litt. _c_.

_e._ Quinta et minima polyporum species, maxime aucta magnitudine adhuc delineata fig. 1. tab. IX.

_f._ Cellulæ, quas quarta species habitat.

_Fig._ V. Corallina erecta pennata denticulis alternis caule appressis: in hac nulli erant polypi nisi in cellulis circumcirca truncam affixis _a a_.

_b._ Cochleæ magnitudine auctæ in B.

_c._ Eschara millepora minima crustacea cellulis tubiformibus, animalculis domicilio inserviens, et magnitudinæ auctæ in C.

_Fig._ VI. Corallina abietis forma, quam mense Decembri accepi: ejus rami vesiculis vel ovulis _a_, _a_, per paria ordine quadam positis, erant obsessi.

A. Talis vesicula vel ovum microscopio visum.

_b._ Cochleæ, & _c._ Eschara minima, ut in præcedente figura magnitudine aucta in B et C.

_d._ _d._ Dua corpuscula fusca, quæ microscopio visa nidum vermium referunt in D.

_Fig._ VII. Corallina pennata et siliquata, ab ostreo abstracta: in hac præter tres polyporum species

_a_ A, _b_ B. (quæ cædem ac in fig. II.) _c_ C, sex alia insecta reperire contigit, quæ delineata sunt in tab. X. fig. 1, 6, 8.

_I. Rhodius ad vivum pinxit._ _J. Mynde sc._]

TABULA NONA.

_Fig._ I. Minimorum polyporum marinorum genus, cum polypis ramosis (_polypes à bouquet_) aquæ dulcis conveniens.

A. talis polypus conservæ marinæ viridi insidens vix oculo nudo conspicuus.

B. idem lente oculari, et in C fortiore visus microscopio.

_Fig._ II. Polypus coccineus, quem tabulæ secundæ

_Fig._ III. & IV. naturali et aucta magnitudine exhibent, hic fortissimo microscopio visus.

A. hic polypus expansis brachiis, prædam expectans.

B. idem brachia contrahendo, prædam arripiens.

_a._ Brachia majora inferiora numero 16, 18, vel 20.

_b._ Brachia superiora breviora numero 12, 14, vel 16.

_c._ Corporis pars superior pyriformis, inferiori infixa.

_d._ Corporis pars inferior compressa.

_e._ Locus, ubi polypus corallinæ inhæret.

C. idem polypus a parte anteriore visus, cum corporis partem superiorem pyriformem in globulum contraxerat, quod in majoribus polypis (vide infra fig. IV, V, VI.) magis visibile.

_Fig._ III. Similis polypus coccineus, cæteris major, ex cujus corpore (ubi partes _c_ et _d_ conjunguntur) octo ramuli enascebantur, qui in summitatibus duos vel tres gerebant globulos, punctum rubrum in medio habentes, et quos in polypos juniores excreturos fore speraveram frustra.

_a._ Hujus polypi brachia longiora inferiora.

_b._ Brachia breviora superiora.

_c._ In medio corporis pyriformis os polypi esse videtur.

_Fig._ IV. Majus, ut videtur, genus polyporum, quos _klapkonten_ vocant, ostreorum conchis insidentium, quorum hic, rudius attractum, brachia penitus in corpus suum abscondit.

_Fig._ V. Idem polypus corpore extenso brachia expandens.

_Fig._ VI. Idem capta præda se contrahens.

_I. Rhodius ad vivum pinxit._ _J. Mynde sc._]

_I. Rhodius ad vivum pinxit._ _J. Mynde sc._]

TABULA DECIMA.

_Fig._ I. Tres species animalculorum lucentium in guttula aquæ marinæ fortiore microscopio visorum.

_Fig._ II. Mirum animalculum in corallinis a doliis marinis coniformibus abrasis repertum.

A. tales minores erant centeni.

B. decem vel duodecim erant hac magnitudine naturali.

C. idem animal microscopio visum.

_a._ Antennæ.

_b._ Primum par pedum vel brachiorum.

_c._ Secundum par.

_d._ Tertium et maximum par.

_e_, _e_, _e_, _e_. Quatuor corpuscula oviformia, quæ animal ut movebat natando.

_f_, _f_, _f_, _f_, _f_, _f_. Sex pedes posteriores, quibus simul corallinæ ramum arripiens, quaquaversum se flectore poterat.

_g._ Cauda in cujus extrema parte anus.

_h._ Oculi.

_Fig._ III. Aliud animal in iisdem corallinis repertum.

A. illud animal pronum.

B. supinum.

C. fortiore microscopio visum.

_Fig._ 1, 2, 3, 4, 5, 6, 7, 8. exhibent quasdam noctilucas, et alia animalcula in diversis corallinis reperta, ea magnitudine, qua tertia et quarta lens microscopii à Dº. Cuff in Anglia fabrefacti illa ostendit.

Animalculum _c_, fig. 8. mirabilissimæ erant structuræ, et plurima habebat membra.

XXXIII. _Remarks on Dr._ Job Baster’s Observationes de Corallinis, &c. _printed above, p. 258. In a Letter to the Right Honourable_ George _Earl of_ Macclesfield, _President of the R. S. from Mr._ John Ellis, _F.R.S._

[Read June 9, 1757.]

My Lord,

I HAVE read Dr. Job Baster’s letter to the Royal Society; wherein he endeavours to prove, that corallines are not of an animal, but a vegetable nature; and has brought many arguments to support his system; which, to gentlemen not well acquainted with the subject, may appear plausible.

I could have wished the Doctor had read and examined thoroughly what has been lately written on the subject: I then should not have had occasion to trouble your Lordship with the following remarks, which I find necessary to support what I have already advanced on that head.

His first argument is, That because he does not find as many polypes in the corallines adhering to ships, flood-gates, and buoys, as in deep water on oysters, muscles, and rocks, therefore he concludes, that corallines are not formed by polypes.

In answer to this, let us examine the pliable structure of these bodies, and how wisely nature has defended such tender substances with a tough thin membranaceous covering, and we shall find, that the sea is calm enough often near the surface to give them time to grow, even in the strongest currents: but, without doubt, they are more liable to be destroyed in such agitated situations, than in the calm depths of the sea.

His second argument is, That finding polypes are not equally dispersed over the whole plant, how can they form it? and gives us an example, _Tab._ VIII. _fig._ 5. of a coralline, that is incrusted with many other corallines or polypes on the stem, but has none on the branches.

Here we plainly see the mistake: the Doctor looks for the tender part of the polype on the surface of the coralline, considering it as a plant; and indeed, if this was the case, he ought so to do; but he never once takes notice of the internal hollow structure of the stem, branches, and denticles of those bodies, to inform us whether he found an animal in those parts or no. This material point he seems not to have thought on; which is really the true point in controversy at present among gentlemen, who have not examined these bodies recent in sea-water.

His third argument is, That almost always one and the same coralline plant cherishes polypes of different kinds; and refers us to Tab. VIII. fig. 2. and 4.

In fig. 2. he gives us an elegant painting of a geniculated red conserva for a coralline, surrounded, as is very common, by many species of small corallines and escharas. And in fig. 4. he gives us a drawing of one of the tubular corallines, with the head of the animal at the top of it; the stem of this is incrusted with four different corallines and escharas, like the conserva fig 2.; and then he asks, which of these five polypes made the tubular coralline?

To give him some proof of the animal nature of this coralline, let him consult Ray’s Synopsis, ed. 3. p. 34. n. 4. and there he will find one of his species, called _adianti aurei minimi facie planta marina_, taken notice of so long ago as the year 1713. by Dr. Lloyd, as a zoophyte, from its stem or tube’s being full of a thick reddish liquor, rather resembling blood than the juice of a plant; which, upon pressing the stem, communicated with the little head at top.

His fourth argument is, That as upon one and the same coralline plant you shall find different kind of polypes; so, in different species of coralline, the same polypes; and, to confirm this, he quotes my Essay on Corallines; where I have remarked, that the polypes in the denticles of the setaceous or bristly coralline, Nº. 16. appear to be like those, that are on the lobster’s horn coralline, Nº. 19. And to illustrate this, he observes, that bees and wasps always build their cells invariably the same; and that therefore these two corallines should be the same.

But herein he takes this matter wrong: he has considered, in all his observations, the heads of those parts of the polype, in which are the mouths, arms, or tentacula, which appear coming out of the cups, denticles, and at the ends of the tubes of the corallines, as so many whole and intire animals, without every observing, that the body of the animal is contained in the tubular part of the root, stem, and branches; and that these differ from one another widely both in size and shape, as he may plainly see in the two corallines he has instanced: for the more exact drawings of which, I shall refer him, _viz._ for the setaceous or bristly coralline, to my Plate, Nº. 38. the natural size of which is at fig. 4. and the magnified one at fig. D: this he will observe to have a small stem, and its branches disposed in a pinnated form: and for the lobster’s-horn coralline, I shall refer him to Tab. xxii. of Vol. xlviii. of the Philosophical Transactions; where, at Nº. 3. the natural size is expressed, and at C the upper part of this coralline is drawn in proportion to the bristly coralline from the same magnifying glass; which shews the stem to be much larger, and surrounded by its branches growing in whorles at equal distances, not unlike the equisetum, or horse-tail plant; and yet the heads of this animal nearly resemble the other, only a little larger. Further, his comparison to bees and wasps, and their cells, is not conclusive: for these ramified, hollow, and denticulated bodies, called corallines, which we so frequently find dead on our shores, are properly skins of certain marine polypes, and not nests, as those constructed by these little winged animals are. And yet we find as great a regularity in the same species of these corallines, as when we compare two oak trees to one another, or two of Mr. Trembley’s branched fresh-water polypes to one another.

He then proceeds to his fifth argument, That if corallines were formed by polypes, neither the polypes, nor even their cells, would ever fix on living animals, or any other bodies.

Here we may observe, that the consequence he draws doth not follow; for corallines may be formed or produced by certain species of polypes, and yet polypes of another species may be found adhering to other bodies, and even to animal bodies.

By his sixth argument he endeavours to prove, That the vesicles, which are found in regular rows on the sea-fir coralline in winter, Tab. VIII. fig. 6. do not belong to it; and are no more than the eggs of some sea insect deposited on it, of which there may be a great variety.

But to convince him of his mistake, let him take off one of the vesicles, and apply a large magnifier to the place, and he will discover a hole, by which this vesicle or ovary has had a communication thro’ the skin with the parent polype. For a further illustration of the manner in which these vesiculated polypes breed, let him consult the 38th Plate of my Essay, where he will find several accurate figures (drawn by Mr. Ehret from the life) of these vesicles, with the spawn of the polypes coming out of them; some of which spawn we evidently discovered to be young polypes with their arms formed; and, as they fell from the vesicle, extending themselves in the watch-glass of sea-water.

In examining the drawings for his plates, I have observed, that Tab. VII. fig. 2. is evidently a red conserva, which he calls a coralline. We have no corallines, but many conservas, of this form and bright red colour on our coasts; and these shores, I believe, are allowed to have similar marine productions with those of Holland.

Tab. VII. fig. 5. he calls a branch of red coralline, which he says he kept several weeks in sea-water, and that often changed; during which time it sprouted and grew very much. This experiment, I am persuaded, is very true; because it is plainly a vegetable, as appears from his own exact drawing of it; and seems to be the _fucus teres rubens minus in longnum protensus_ of Ray’s Synopsis, ed. 3. p. 91. N. 53. This is one of his principal arguments to prove the vegetation of corallines.

Tab. VIII. fig. 1. he calls a branch of red coralline; and at fig. 2. he has it magnified, where it appears to be a geniculated red conserva, drawn and painted with great exactness.

These arguments, my Lord, and these figures of real vegetables, which the Doctor has given us for corallines, shew, how much he is willing to support the old opinion of the botanists: but I am satisfied he will soon alter his opinion, when he observes the remarkable difference of the texture of vegetable and coralline bodies, when viewed in sea-water thro’ a good aquatic microscope. And to convince him more fully, that corallines are an animal substance, let him burn them, and he will perceive the same pungent volatile alkaline smell, which he finds in burning horn, hair, or oysters; whereas burnt fucus’s and conservas yield a smell not much unlike that of common land vegetables. Even the stony corallines, when their cretaceous covering has been dissolved in vinegar, the membranous part, that remains of them, put into the fire, yields the same animal smell with other corallines.

Further, since I find the Doctor has promised the Royal Society to continue his researches at the seaside, the following hints may be of use to him. And, first, he will find, that those he seems to think naked polypes, which he found adhering to corallines and other bodies, are really small corallines and escharas, with their proper skins and cells; all which I have particularly described already. I would then recommend him to examine such corallines as are taken out of the deepest water, which are found adhering to shells and fucus’s. He will find Mr. Cuff’s aquatic microscope, or one of that form, the most commodious for observing these animals alive.

The most transparent ones he will find the best to discover their gelatinous inside, which runs thro’ the stem and ramifications, and ends in the heads, where the claws are. Some of the best kinds to observe are as follows: The sea-oak coralline, the lily-flowering coralline, the great tooth coralline, the sea-thread coralline, and the branched tubular coralline. Pieces of these should be cut off while they are in the sea water, and placed in watch-glasses full of the same: in these they should remain a while, till they recover themselves; and when they are placed on the stage of the microscope, the motion of the internal part communicating with the heads will be easily discovered.

If the Doctor will immerse some of these corallines, when they are extended, in two thirds of spirit of wine and one third of clear sea-water, it will preserve them many years, as I have experienced. He may then put the different sorts into distinct phials, and view them at pleasure with a lens of about one inch and half focus.

In fine, my Lord, opportunities so seldom offer at the sea-side to make these experiments with accuracy; and likewise to this, the strong lines of vegetation that these bodies carry in their appearance, and your Lordship will not be surprised, that there are so many gentlemen, even of the Royal Society, that totally disbelieve them to be animals.

Many there are in the Society, that are wavering between both opinions. If then, my Lord, you think, that any specimens which I have, or any demonstrations tending to clear up this point, that lie in my power, will be acceptable to your Lordship and the Society, your Lordship may freely command them, whenever you think proper, from

Your +LORDSHIP’S+
Much obliged and most obedient Servant,
John Ellis.

London, June 9. 1757.

XXXIV. _An Account of an extraordinary Operation performed in the Dock-Yard at_ Portsmouth: _Drawn up by Mr._ John Robertson, _F.R.S._

[Read May 26, 1757.]

THE Royal William, a first rate man of war, built about 40 years ago, having, upon examination, been judged in so good a state, as to be worthy of repairing for sea service, was ordered into dock, and brought thither on the 29th of June 1756. On these occasions it is usual to lay across the middle line of the bottom of the dock, at distances of about five feet from one another, thick pieces of oak timber of about four feet long; their upper surfaces lying in the same plane, or so posited, that a line stretched from the two extreme blocks will touch all the intermediate ones; and on the middle of these blocks the keel of the ship is to rest. On the said day the tide did not rise so high as was expected; and there was not quite depth enough of water to float the ship in, and set her on the blocks, notwithstanding the assistance of an empty lighter, which, being fixed to the stern, lifted the ship at the end six inches: and as the officers knew they should not have so much water again before the next spring-tides, they were determined to heave her in; which is a very common operation in most dock-yards. Now it so happened, thro’ the great weight of the head and stern, that the ship cambered very much; that is, her keel, from being straight, was become much curved, the two extremities hanging lower than the middle part by many inches; and consequently the foremost part of the keel, instead of sliding over the blocks, forced all the foremost ones away, for above 60 feet; whereby that part of the keel rested on the bottom or floor of the dock, and the aftermost part rested on such of the blocks, as had escaped the violence, which had displaced the others. In this situation the keel was very far from being strait; and so it was resolved to lift by main force the head of the ship, until the keel should be strait; and in that position to support it by the blocks, which had been forced away from their places.

For this purpose there were set up, under the wales and other parts of the ship, to the length of near 80 feet of the stem, as many shoars, as were judged necessary; and also nine pair of bed-screws, three pair under each bow, and three pair under the knee of the head. At each shoar a workman was appointed, to drive wedges between the heels of the shoars and the parts of the dock whereon they rested; whereby the shoars were raised end-wise, and consequently the body of the ship lifted at the same time. While this was doing, the 18 screws were also at work: and between these efforts the fore part of the ship was raised upwards of 19 inches, so much being necessary to bring the fore part of the keel in a right line with the hinder part.

In this service were employed about 270 men; whereof about 144 worked at the screws, and the others worked at the shoars with their mawls and wedges; and the whole operation was performed in about seven hours.

My curiosity leading me to inquire what was the weight of the ship, in the condition she was at the time of bringing her into the dock; for this purpose I procured draughts of the elevation and section, and of the plans at the line of floating, and at the parallel sections of every foot distance down to the keel. Then, by finding the mean area between every two sections, I was thereby enabled to come at the magnitude of a solid, that would nearly fill the trough the ship made in the water; and, by increasing this magnitude by that of the keel, and so much of the stern-post and stem, as were under water, the cubic feet of the fluid displaced by the ship were obtained, being 54869; and consequently her weight was 3532091 pounds, or 1576 tons, 16 _C_. 2 qrs. 3 ℔. These numbers were not altogether so easily come at, as they would have been, had the ship swam on an even keel, her draught of water before being 13 feet 2 inches, and abast 16 feet 6 inches. However, the computation may be esteemed as correct as the nature of the subject would admit; because I found pretty near the same solidity by another method.

I got a block or model made, by a scale of a quarter of an inch to a foot, of so much of the Royal William’s body, as was immerged, when she was brought into dock; and this block I immersed in a trough of sea-water, and found its weight in the following manner.

The length of the trough was 46 inches, breadth 14 inches, and depth 8 inches: at each corner was a graduated scale of inches, and pencil-lines drawn round the inside of the trough at every inch. Sea-water was poured into the trough to the height of 5 inches; and the trough was exactly levelled, by means of the pencil-line, at 5 inches: then the block being forced under the water’s surface, the fluid, when still, was risen to 6⅓ inches; consequently the magnitude of the block was equal to a parallelopipedon of 46 inches long, 14 inches broad, and 1⅓ inches deep, or to 858⅔ cubic inches.

Now 858⅔ cubic inches are equal to 0.4969 cubic feet.

And a cubic foot of sea-water weighs 64.373² pounds avoirdupoize.

Then 64.373² × 0.4969 = 31.987 pounds.

So that by a quarter inch scale, a model similar to the Royal William weighs near 32 ℔.

But a quarter inch scale is ⅟48 of a foot scale.

And the model is to the ship as 1³ is to 48³, or as 1 is to 110592.

Then 3537506 ℔. (= 110592 × 31.987), or 1579 tons, 4 _C._ 3 qrs. 14 ℔. is the weight sought.

The difference by the two methods amounts to 5415 ℔. or to 2 tons, 8 _C._ 1 qr. 11 ℔.

Some of the persons present at this experiment read the height of the water at 6⅜ inches: the difference between 6⅜ and 6⅓ inches is ⅟24 of an inch; a difference easily to be made by different persons in an experiment of this kind. But observing, that the computation made on 6⅜ inches amounted to near 50 tons more than on 6⅓ inches, I caused the trough to be diminished in its depth to 6½ inches, had one of the ends cut off, and a board fixed on the open side, being desirous of making the experiment with the trough standing on one end: and indeed, in this situation, an error of ⅒ of an inch in the height of the water makes a difference of about 16½ tons in the weight of the ship. Into this upright trough water was poured to the height of 36 inches; and the block being immerged, the water was raised 9⅓ inches: so that the block was equal in magnitude to a parallelopipedon of 14 inches long, 6½ inches wide, and 9⅓ inches deep, or to 849⅓ cubic inches: from whence I find the weight of the ship to be 1562 tons, 1 _C._ 2 qrs. 16 ℔. And altho’ I take this number to be nearest the truth, yet it may be observed, that it is no easy matter to come at accuracy in this subject by any of the methods in common use.

My next inquiry was, to find how much of this weight was lifted, and how to proportion it among the screws and mawl-men: but in this, less accuracy must be expected than in the preceding inquiry; for the exact number of men employed is not known; neither can it be told, how many worked at the screws, and how many with the mawls; and only a guess can be made at the part lifted. However, something may be gathered, which may, perhaps, be worth the knowing.

Let the weight raised be taken at half the weight of the ship; for 64 feet, the length of the keel raised, is not far from half the whole length: add to this the sally of the head, the weight of the forecastle, the friction of the timber, and the resistance of the parts bent by the cambering: beside, the mawls worked at several shoars set up abast the said 64 feet.

Now the weight by the last experiment was 3499064 pounds: one half, or 1749532 ℔. I take to be the weight raised between the screws and mawls.

The distance between two contiguous threads of each screw was 1⅓ inches; the length of the two opposite levers was 12 feet 8 inches, or 152 inches, and described a circumference of 477½ inches: each screw was worked by 8 men: their force, reckoned at 30 ℔. each, makes the power working on each screw equal to 240 ℔.

Hence, from the known property, each screw could raise 65485 ℔.

And the 18 screws raised 1178730 ℔.

Then there remained 570802 ℔. to be raised among about 126 mawls:

Which gives 4530 ℔, or a little more than two tons, to be raised by each man with his mawl and wedges; which is considerably less than what I have seen raised by way of experiment.

XXXV. _Observations on an Evening, or rather Nocturnal, Solar_ Iris. _By Mr._ George Edwards, _Librarian of the College of Physicians_.

_To the Reverend Dr._ Birch.

[Read June 16, 1757.]

SIR,

ON Sunday evening the 5th of June 1757, being walking in the fields near Islington, about half a mile north of the upper reservoir or bason of the New River, I observed the sun to sink beneath the visible horizon to the north-west, it being very clear in that quarter, except some thin clouds a little above the horizon, which were painted of fine red and golden colours, as is usual when the sun sets in a calm clear evening. But about 20 minutes after sun-set, as near as I could judge, it then being darkish, I was greatly surprised to see an Iris in the dusky air, at a height greater than is seen at any time in the rainbow. It was in the contrary quarter of the heavens to the setting sun, and fell on the smoke, mists, and evening vapours arising from the city of London and its neighbourhood. The arch seemed to be a full half circle, tho’ its lower parts fell some degrees short of the horizon. It was very distinctly seen for about 15 minutes. Its colours the same as in the rainbow, but fainter. The lower ends of the bow arose gradually higher from the earth, as the sun declined beneath the horizon, until the whole arch disappeared. The center of the arch was above the horizon at its first appearance. What most perplexed me, was, to find the cause of this painted arch. I could not believe, that it proceeded from the sun-beams falling on rain; for there had been none that afternoon; nor was there any sort of signs of rain or rainy clouds to be seen; the wind being northerly, and the air cool, and somewhat hazy in the quarter where the bow appeared; which was not near so bright as the rainbow appears to be in the day-time; and I believe, that it would not have been visible at all in the presence of the sun. I imagine it was formed on the gross particles of the evening vapours, mixed with those of the smoke arising from the town; for had the sun-beams shot from beneath the horizon on falling rain at a considerable height above the earth, I believe the darkness would have rendered the appearance of such a bow far brighter than it appears to the sight in the presence of the sun: but this night or evening arch being reflected, as I suppose, from particles so minute as those of floating vapours, gave but little light and colour to the sight, and what would not have been visible, had the sun been above the horizon. For the same reason, the moon and stars are visible in the absence of the sun, and, on the contrary, are unseen when the sun is present: and if we light a candle, and set it in the sun-beams, the flame is lost to our sight, tho’ the same candle will give us a considerable share of light in the night. As I have never before seen or heard of such an arch, I thought this account of it (imperfect as it is) might not be disagreeable to the Royal Society.

It could not be a lunar arch, the moon being then many degrees below the horizon, and the arch in a place, where it could not be affected by the moon’s rays. The consciousness of my inability to give a proper account of such an uncommon appearance could not deter me from the attempt.

I think I have said all that is necessary on this subject; yet am ready to answer any question for the farther illustrating of it. I am,

Reverend Sir,
Your most humble Servant,
Geo. Edwards.

College of Physicians, London, June 6th, 1757.

XXXVI. _The Effects of the_ Opuntia, _or Prickly Pear, and of the_ Indigo _Plant, in colouring the Juices of living Animals. Communicated by_ H. Baker, _F.R.S._

[Read June 23, 1757.]

June 23d, 1757.

MR. Baker received a letter yesterday from Dr. Alexander Garden, of Charles Town in South Carolina, part of which he hopes he shall be excused for laying before the Royal Society.

The Doctor writes thus:----“As you desired, I tried the effects of the prickly pear in colouring the urine. A few days after your letter, I went down to one of the islands, and gathered some of the fruit, and gave four of the pears to a child of three years of age, and six pears to one of five. The next morning I examined the urine of both, and it appeared of a very lively red colour, as if tent-wine had been mixed with clear water. The urine of the eldest was deeper coloured, and of a darker look: the youngest (who always naturally made clear urine) was of a more lively and beautiful red. Next day I gave six pears to a Negroe wench, who gave suck, and strictly forbad her suckling her child for six or eight hours; and then taking some of her milk in a tea-cup, and setting it by for some hours, the cream had a reddish lustre, tho’ it was very faint.

I was led to this last experiment by an observation, which I made on the milk of cows, who had fed in an indigo-field; the indigo had not only tinged their urine blue, but the cream of the milk was of a most beautiful blue colour, and had a radiated appearance from the centre (Is it not hence probable, that the dye is the oily part of the plant?). The milk underneath was clear and white as usual.”

Dr. Garden wrote, a year ago, that the prickly pear grows in great abundance about Carolina; and also that the cochineal insects are found upon it; but hitherto no attempts have been made to cure them as the Spaniards do. In hope, that some rich dye may be produced from the plant itself, Mr. Baker proposed some experiments to Dr. Garden, which he intends to prosecute this summer.

XXXVII. _Account of an extraordinary Shower of black Dust, that fell in the Island of_ Zetland _20th_ October 1755[194]. _In a Letter from Sir_ Andrew Mitchell, _of_ Westshore, _Bart. to_ John Pringle, _M.D. F.R.S._

[Read June 23, 1757.]

Pall-Mall, June 9th, 1757.
SIR,

IN compliance with your desire, I made particular inquiry, whether at or about the time the earthquake happened at Lisbon the 1st of November 1755. any uncommon phænomena were observed to appear in the islands of Orkney or Zetland, as such had happened about that time in other parts of Scotland. From Orkney I was informed, that nothing particular had happened; only, that about the time mentioned the tides were observed to be much higher than ordinary. I received from Zetland a letter, dated 28th May 1756. from Mr. William Brown, Master of the grammar-school at Scalloway in that country, a sensible and observing man; wherein he writes verbatim as follows. “Blessed be God, notwithstanding the great devastations, that have been made in other parts of the world by earthquakes, we have been intirely free from any disaster of that nature: nor has any thing extraordinary happened in this country since you left it; only on Monday the 20th October last, betwixt the hours of three and four in the afternoon, the sky being very hazy, as it uses to be before a storm of thunder and lightning, there fell a black dust over all the country, tho’ in greater quantities in some places than in others. It was very much like lampblack; but smelled strongly of sulphur. People in the fields had their faces, hands, and linen, blackened by it. It was followed by rain.----Some people assign the cause of it to some extraordinary eruption of Hecla. But I shall trouble you no more about it, as no doubt some of your friends have written to you of it some time ago.”----

In June 1756. I returned to Zetland; and, upon further inquiry, found what Mr. Brown had written me was attested by Mr. Mitchell, parson of the parish of Tengwall, and by several Gentlemen of credit and reputation, who had seen and observed the same phænomenon in different parts of the country at the time above-mentioned.

Mr. Brown having omitted to mention, how the wind did blow at the time the black dust was observed, I made particular inquiry about that circumstance, and found it was from the S. W. which does not seem to favour the opinion, that the dust proceeded from an eruption of mount Hecla, which lies about N. W. from Zetland; unless it may be supposed, that a north wind happening just before had carried this dust to the southward, and the south-west wind immediately following had brought it back to the northward. But, in this case, would not this black dust have been observed in Zetland at its first travelling to the southward? Upon inquiry, I did not hear it was.

Thus far I have obeyed your commands, which I will always do with pleasure; and if you think it worth while to lay this letter before the Royal Society, I leave you at full liberty to do so, or not, as you think proper: but what it contains may be relied on as truth. I am, with great regard,

Dear Sir,
Your most obedient humble Servant,
And. Mitchell.

_P.S._ I may add, that the distance from mount Hecla to Zetland is between 500 and 600 miles.

XXXVIII. _A Description of some Thermometers for particular Uses. By the Right Honourable the Lord_ Charles Cavendish, _V.P.R.S._

[Read June 30, 1757.]

THE thermometer (TAB. XI. _fig._ 1.) is designed for shewing the greatest degree of heat, which happens in any place during the absence of the observer. It consists of a cylinder of glass joined to a tube, and differs from common thermometers only in having the top of the stem drawn out into a capillary tube, which enters into a glass ball C, joined on to the stem at the place where it begins to be contracted. The cylinder, and part of the tube, are filled with mercury; the top of which shews the common degrees of heat as usual. The upper part of the tube above the mercury is filled with spirit of wine, and some of the same liquor is left in the ball C, so as to fill it almost up to the top of the capillary tube.

Now when the thermometer rises, the spirit of wine will be driven out of the tube, and will fall into the ball C. When the thermometer sinks again, as the spirit cannot return back from the ball, the top of the tube will remain empty, and the length of the empty part will be proportional to the fall of the thermometer. Therefore, by means of a proper scale, the top of the spirit of wine will shew how many degrees it has been higher than when observed; which being added to the present height, will give the greatest degree of heat it has been at.

_J. Mynde sc._]

To fit this thermometer for a new observation, it is necessary to fill the upper part of the tube with spirits; which may be done, by inclining the instrument till the spirits in the ball C cover the end of the capillary tube. For if the cylinder is then heated, by applying the hand to it, or by the flame of a lamp held at some distance, till the spirits rise to the top of the tube and run over into the ball C, and is then suffered to cool in the same position, the tube will remain full of spirits, and the thermometer will be fitted for a new experiment.

The top of the capillary tube is made to stand pretty near to one side of the ball, and also to the top of it, that a less inclination of the instrument may be sufficient to make the spirit of wine in the ball cover the end of the tube.

The ball C is joined on as high as possible, so as to hide no part of the tube, except that, where the bore is contracted. By this means, the top of the spirit of wine begins to appear before the thermometer has sunk one degree.

It will be convenient to leave some mercury in the ball C, which may be made to cover the end of the capillary tube, by inclining the thermometer more than what is necessary to make the spirit of wine cover it. By this means some mercury may be got back into the tube, in case any of it should happen to be driven into the ball by the thermometer’s being exposed to too great a heat.

The scale of degrees at top, which shews the descent of the thermometer from the highest point it has arrived at, ought not, in strictness, to be the same at all times of the year; for those degrees exceed the common degrees of heat pointed out by the top of the mercury, as much as the column of spirit of wine expands, and therefore are greatest when that column is so; that is to say, when the greatest heat to which the instrument has been exposed is least. A difference of 30 degrees of Fahrenheit’s scale, in the greatest rise of the thermometer, would require the scale to be altered one sixtieth part: and the error arising from making use of the same scale will be about one sixth of a degree, if the thermometer is observed when it has fallen ten degrees.

In the instrument here described, the bore of the tube is about 0.027 inches; and one inch of it contains two grains of mercury, and answers to about ten degrees, the cylinder containing about 2280 grains. If a much shorter tube was made use of, a considerable error might arise from too great a quantity of spirits adhering to the sides of the tube, in that part, which is filled with mercury; especially when the thermometer rises fast. This makes it necessary to employ a cylinder of a considerable bigness, if it is desired to have the scale of degrees pretty large.

If the weight of the mercury is thought inconvenient, it may be avoided by the construction described in fig. 2. where the bottom of the tube is bent so as to point upwards, and is joined to a ball A, which communicates with a cylinder placed above it. In all other respects it is the same as the instrument before described.

It is filled with spirit of wine and mercury; the quantity of the latter being sufficient to fill the whole tube and the ball A.

No part of the spirit, with which the cylinder is filled, can get into the tube, as long as the instrument is kept in an erect position, or even if it is carefully laid down flat on a table. For tho’ in this last case some of the spirits may get into the ball A, it will rise to that part of the ball, which is then uppermost, and will not touch the orifice of the tube _n_; which was the reason for adding this ball, which would be unnecessary, if the instrument was kept constantly erect, or nearly so. If the spirit should come to touch the orifice of the tube _n_, it would work up between the mercury and the glass; which would put the instrument out of order.

The thermometer fig. 3. is designed for shewing the greatest cold, which happens in any place during the time the instrument is left in it. The tube is bent into the shape of a syphon of unequal legs standing parallel to one another, the bend being at the bottom. The top of the shorter leg is bent to a right angle, and immediately opens into a ball A, which, by means of a short bent tube on the opposite side, communicates with a cylinder standing parallel to the legs of the syphon, and pointing downwards. This cylinder contains the greatest part of the fluid; and is added only to make the thermometer more sensible than it would be, if the ball A was made of a sufficient bigness to contain the proper quantity of fluid. This instrument is filled with spirit of wine, with the addition of as much mercury as is sufficient to fill both legs of the syphon, and about a fourth or fifth part of the ball A.

The common degrees of heat are shown by the top of the mercury in the longest leg, or by the top of the spirit, in case any of it is left above the mercury.

When the mercury in the longest leg sinks by cold, that in the shorter leg will rise, and will run over into the ball A; from whence it cannot return back when the thermometer rises again, as the surface of the mercury in the ball is below the orifice of the tube _n_. Therefore the upper part of the shorter leg will be filled with a column of spirits of a length proportional to the increase of heat; the bottom of which, by means of a proper scale, will show how much the thermometer has been lower than it then is; which being subtracted from the present height, will give the lowest point that it has been at.

If no further contrivance was used, the mercury would fall into the ball A in large drops; which would make the instrument less accurate. For the thermometer’s beginning to rise immediately after a drop is fallen, or just as it is going to fall (in which case it will return back into the tube), will make a difference of such part of a degree nearly as that drop answers to. To prevent this inconvenience, the top of the shorter leg, close to the ball, is contracted, by being held in the flame of a lamp; and the passage is further streightened by a solid thread of glass placed within the tube, and extending from the bottom of the shorter leg to the part near the ball A, where it is most contracted. By this means, as soon as any small portion of mercury is got beyond the end of the thread of glass, it breaks off, and falls into the ball in very small drops. This thread of glass is fastened by the heat given to the tube in making the bend next to the ball. In order to fill the shorter leg with mercury, to fit the instrument for a new experiment, it must be inclined till the mercury in the ball covers the orifice of the tube _n_. The cylinder being then heated, the mercury will be forced into the shorter leg, and will run down the thread of glass in drops, which will soon unite. By this means, such a quantity of mercury must be got into the shorter leg, as, upon the cooling of the instrument, will be sufficient to drive all the spirit of wine into the ball with a less degree of cold than what the thermometer is likely to be exposed to.

The ball A must always have some mercury in it, but never enough to fill it up to the orifice of the tube _n_. It must therefore be made of such a size, as to contain all the mercury, which can come into it from the tube without being too full. If it should happen to be made too small, so as to be too full in cold weather, any part of the mercury may easily be driven into the cylinder, and got back again into the ball when wanted in warmer weather.