The history of the Royal-Society of London for the improving of natural knowledge by Tho. Sprat.
Sprat, Thomas, 1635-1713., Cowley, Abraham, 1618-1667. To the Royal Society.
Page  183

Mr. ROOK'S DISCOURSE Concerning the Observations of the Eclipses of the Satellites of Iupiter.

LOngitudinis sive Differentiae Meridianorum scientia est vel Nautica, vel Geographica.

Illa Navis aquae innatantis; Haec Vrbium, Insula∣rum, Promontoriorum, &c. Globo terrestri adhaerentium situm investigat.

In Navi, motu vario subinde translatâ; Observatio identidem est repetenda; at loci terreni, fixam perpetuò sedem obtinentis, positionem semel determinasse sufficit.

Maria, fluctibus ut plurimum agitata, subtilem Instru∣mentorum, praesertim Telescopii longioris tractationem minime permittunt.

Longitudinis Scientia Nautica vix unquam de Caelo expectanda: Geographica vero ab Eclipsibus Corporum coelestium praecipuè petenda.

Eclipses sunt vel

  • Veteribus notae, scil. Solis & Lunae
  • Satellitum Iovis, ante Tubi Optici usum incognitae.
(Missam fecimus Cl. Hugenii Lunulam Saturniam, Ob∣servatu difficiliorem.)

Illarum per multa retro saecula Observationes; nè duo quidem loca quantum Meridianorum intercapidinem habeant, satis certò definitum esse Experimur: harum verò per pauculos annos adhibendâ diligenti animad∣versione; Page  184 praecipuae totius terrarum Orbis partes, quomo∣do ad se invicem sitae sint, accuratiùs determinatum ir i non desperamus.

Causae, ob quas minùs in hoc negotio praestitêre Eclipses Luminarium,

Sunt
1. Communis, utrisque ipsarum Raritas
Propria
2. Solari, Parallaxis Lunae.
Propria
3. Lunari, Penumbra Terrae.

His ergo praeferimus Satellitum Iovialium defectus frequentissimos, sine ulla Parallaxi, in quibus etiam pen∣umbra Iovis prodesse magis, quam officere videtur.

Methodus Longitudinis, ex Eclipsibus vel aliis Phae∣nomenis Coelestibus, indagandae àuplex est: Vna, cum tempore ad Meridianum Tabularum proprium supputato, tempus alibi observatum; Altera, tempora variis in lo∣cis observata, inter se comparat.

Cum Arti Nauticae Prior illa unicè interserviat quae motus coelestes accuratiùs multò, quam nobis sperandum videtur, cognitos supponit; ob Astronomiae imperfectio∣nem, & observationum Marinarum hallucinationem per∣petuo ferè necessarium: supra pronunciavimus Longi∣tudinis Scientiam Nauticam vix unquam de Coelo ex∣pectandam.

Methodus altera, Geographiae perficiendae idonea, cum non aliam ob causam praevium Calculum adhibeat, nisi ut eo moniti plures, eidem Phaenomeno, in dissitis locis, observando simul invigilent; Periodorum atque Epo∣charum 〈 in non-Latin alphabet 〉 minimè desiderat.

Satellites Iovis numero sunt quatuor, varia apud Authores nomina sortiti; nos ex diversis, quae a Iove obtinent intervallis, 1. Intimum, 2. Penintimum, 3. Penextimum, 4. Extimum appellabimus.

Page  185Horum non nisi uniusmodi 〈 in non-Latin alphabet 〉 Observandum pro∣ponimus; immersionem nempè in Vmbram Iovis sive ipsum Eclipseces initium.

Solam hanc 〈 in non-Latin alphabet 〉 seligimus, utpote in indivisibili ferò constitutam: Licet enim luminis languor atque diminu∣tio moram aliquantulam trahere possit, omnimodo tamen Extinctio & Evanescentia (de qua unicé soliciti sumus) momento quasi contingere deprehendetur.

Ante ☍ ☉ ♃ Satellites ad Occidentem Disci Iovia∣lis respectu, in deliquia incidunt; post Acronychia, ad Orientem.

Intimi & (nisi fortè rarissimè) penintimi Eclip∣s••• tantum Occidentalium initia nobis apparere possunt: duorum autem remotiorum multa etiam Orientalium exordia conspicere licet.

Defectus, Medicaeorum observatu faciliores reddant. 1. Major Planetarum claritas. 2. Motus ipsorum tar∣dior. 3. Penumbra Iovis crassior. 4. Longius a Io∣viali Disco intervallum: at Observationum 〈 in non-Latin alphabet 〉 condicit. 1. Motus Satellitum velocior. 2. Penum∣bra Iovis angustior.

Haec omnia nobiscum meditati, subduct â benè singulo∣rum ratione, Satellitum intimum & penextimum ad rem nostram prae coeteris accommodatos; atque adeò cum sa∣tis frequentes sint ipsorum Eclipses, solos adhibendos esse judicamus.

Extimum omninò negligimus utpotè minimum omni∣um & obscurissimum; praesertim verò quod tantâ non-nunquam sit Latitudine praedictus, ut Vmbra Iovis ip∣sum Aphelium neutiquam attingat.

Penintimus autem nullâ gaudet ex suprà recensitis Praerogativâ, quae alterutri saltem eorrum, quos jam praetu∣limus, potiori jure non debeatur.

Maxima, Satellitum in Vmbra incidentium, a limbo Page  186 Disci Iovialis distantia, unâ aut alterâ, post priorem So∣lis & Iovis quadraturam, bebdomada contingit.

Estque ea Penextimi sesquidiametro Iovis ferè aequa∣tis: Intimi verò semidiametro ejusdem non multò ma∣jor sextâ ante memoratam Quadraturam Hebdomada; Penextimus Vmbram ingrediens Diametro Iovis à disco abest: Augendâ indè usque ad maximam distantiâ in∣cremento (non uniformi sed) continue decrescente.

Hinc iisdem reciprocè passibus (decremento sc. sen∣sim increscente) diminuitur istiusmodi intervallum, ad bimestre usque tempus a dictâ Quadraturâ elapsum, quando iterum Diametro Ioviali aequatur.

Posteà autem usque ad ipsa Acronychia, penextimus Vmbram subiturus, aequabili ferê gradu (singulis nem∣pe hebdomadis quadrante Diametri) promotus ad lim∣bum Iovis accedit. Intimi, pro diverso Iovis ad solem situ, distantia eâdem planè ratione variatur: ejus enim, quam ubique obtinet, Penextimus, trienti fere perpetuo est aequalis.

Mense circiter post Iovem soli oppositum, Penextimus (Intimi post ☍ ☉ ♃, immersiones observari non posse suprà innuimus) simul ac corporis Iovialis limbum ori∣entalem transierit, Occidentalem umbra continuo in∣trabit.

Inde augetur paulatim penextimi evanescentis di∣stantia, donec unâ aut alterâ ante posteriorem quadratu∣ram hebdomadâ, maxima evadat; quando a disci Io∣vialis margine semidiametro ejusdem removetur.

Postquam autem hucusque diminutâ sensim velocitate, umbra Iovis ab ipsius Disco recessit: hinc, motu continue accelerato, ad eundem redit.

Per bimestre ante & post Iovis cum sole conjunctio∣nem spatium in locis Longitudine multum differen∣tibus, eadem Eclipsis apparere nequit: adeoque tunc Page  187 temporis observationes instituere non est operae pre∣tium.

Quae cum ita sint, tempus quadrimestre, a sextili priori usque ad ipsa ferè Acronychia numerandum, utrique Sa∣telliti Observando erit unice opportunum: Penextimi autem soli, insuper trimestre, ab altero post oppositionem mense ad sextilem posteriorem.

Intra tempora jam definita, octoginta circiter utrius∣que simul Satellitis fient Eclipses; Penextimi sc. fere triginta, intimi autem quinquaginta.

H••s cum (non ubivis terrarum sed) aliae aliis in lo∣cis sint conspiciendae, in sex Classes digeremus.

1. In Europâ & Africâ
Eclipses ob∣servandas compre∣hendet.
2. In Asiâ.
Eclipses ob∣servandas compre∣hendet.
3. In Americâ.
Eclipses ob∣servandas compre∣hendet.
4. In Europa Africa & Asia.
Eclipses ob∣servandas compre∣hendet.
5. In Europa, Africa & America.
Eclipses ob∣servandas compre∣hendet.
6. In Asia Orient. & America Occident.
Eclipses ob∣servandas compre∣hendet.

Non opus est fortè, ut moneamus in Insulis

  • Oceani Aethiopici observandam esse Classem 4 am.
  • Oceani Atlantici observandam esse Classem 5 am.
  • Oceani Pacifici observandam esse Classem 6 am.

Calculus Eclipsium a nobis exhibendus in ipso fortasse loco ad quem instituitur, plus horâ integrâ nonnunquam à vèro observabit, ob variam se. in Satellitum motu 〈 in non-Latin alphabet 〉 ab Excentricitate (ut verisimile est) & propria∣rum ipsis Orbitarum ad Iovis Orbitam inclinatione ori∣undam.

Alibi autem térrarum multo minus calculo fidendum, propter incertam insuper in plerisque locis Meridiano∣rum Page  188 Differentiam; quae tamen, ut fiat, Reductio tempo∣ris, aliqua utcunque adhibenda est.

Longam itaque futuram sepiuscute Eclipsium harum ex∣pectationem praemonemus, assiduamque interim attentio∣nem, nec (ob 〈 in non-Latin alphabet 〉 admodum 〈 in non-Latin alphabet 〉) unquam fere inter∣ruptam, esse continuandum: primam enim, quam visu assequi possumus, luminis diminutionem, brevissimá (prae∣sertim in intimo) interpositâ morulâ mox insequitur per∣fecta ejus extinctio.

Molestum autem in observando taedium, summa 〈 in non-Latin alphabet 〉 abunde compensabit, idemque plurimum minuit sociorum mutuas operas tradentium, ubi suppetit praesentia.

Ad momenta temporis accuratissime notanda (quod in hujusmodi Observationibus est Palmarium) perutile erit Horologium Oscillatorium, ab ingeniosissimo & candidissi∣mo Hugenio feliciter excogitatum.

Appendix.

LOngitudinis Sientiam Nauticam vix unquam de Coe∣lo expectandam suprà asseruimus: siqua tamen ejusmodi aliquando futura est; non aliud Fundamentum, quam Lunarium motuum praecisam cognitionem, habitu∣ra videtur. Horum autem restitutionem a Parallaxi in∣choandam solertissime monuit Keplerus. Parallaxeus ve∣rò indagandae, & a Lunae latitudine (cui semper ferè complicatur) distinguendae optima (si non sola) Me∣thodus est; quae, in regionibus longe dissitis & sub eodem Meridiano positis, altitudinum. Lunae Meridianarum, per singulas orbitae partes, simul observatarum series inni∣titur: inde enim, Polorum elevatione solum praecognitâ, sertissima innotescit Globi Lunaris à Terrestri distantia. Page  189 Proponimus itaque nos Africae Promontorium Cap. Bonae Spei, vel in Oceano Atlantico Sanctae Helenae Insulam, cum locis in Europá iis respondentibus, Satellitum ope, docuimus, determinandis, in quibus istiusmodi observa∣tiones commodissime instituantur.

Upon the Reading of these last Directions, Mr. Rook the Author of them being dead, I cannot forbear saying something of that excellent Man, which his incomparable Modesty would not have per∣mitted me to write, if he had been living. He was in∣deed a man of a profound judgment, a vast comprehen∣sion, prodigious memory, solid experience. His skill in the Mathematicks was reverenc'd, by all the lovers of those studies: and his perfection in many other sorts of Learning, deserves no less admiration. But above all, his Knowledge had a right influence, on the temper of his mind, which had all the humility, good∣ness, calmness, strength, and sincerity of a sound, and unaffected Philosopher. This is spoken not of one, who liv'd long ago, in praising of whom, it were easie to feign, and to exceed the Truth, where no mans me∣mory could confute me: But of one, who is lately dead, who has many of his acquaintance still living, that are able to confirm this testimony, and to joyn with me, in delivering down his name to posterity, with this just character of his Virtues. He dy'd in the year sixty two, shortly after the establishment of the Royal Society, whose Institution he had zealously pro∣moted. And it was a deplorable accident in his Death, that he deceas'd the very night, which he had for some years expected, wherein to finish his accu∣rate Observations on the Satellites of Iupiter: how∣ever this Treasure will not be lost, for the Society has Page  190 referr'd it to some of the best Astronomers of Europe, to bring his beginnings to conclusion.

*To many of these Queries they have already re∣ceiv'd good returns, and satisfaction: and more such Accounts are daily expected from all coasts. Besides these, there have been several great and profitable Attempts, relating to the good of mankind, or the English Nation, propounded to them, by many publick Bodies, and private persons: which they have again recommended, to be examin'd apart, by divers of their own number, and by other men of ability and integri∣ty, who have accepted of their Recommendations of this kind, the Principal, that I find recorded in their Registers, are these.

They have propounded the composing a Catalogue of all Trades, Works, and Manufactures, wherein men are emploi'd, in order to the collecting each of their Histories: by taking notice of all the Physical Re∣ceipts, or Secrets, the Instruments, Tools, and Engines, the Manual operations or sleights, the cheats, and ill practices, the goodness, baseness, and different value of Materials, and whatever else belongs to the opera∣tions of all Trades.

They have recommended the making a Catalogue, of all the kinds of natural things to be found in Eng∣land. This is already in a very good forwardness. And for its better completing, many Expedients for the preserving, drying, and embalming of all living Creatures have been prosecuted.

They have suggested the making a perfect Survey, Map, and Tables of all the fix'd Stars within the Zo∣diac, both visible to the naked eye, and discoverable by a six foot Telescope, with a large aperture; towards Page  191 the observing the apparent places of the Planets, with a Telescope both by Sea and Land. This has been approv'd, and begun, several of the Fellows having their portions of the Heavens allotted to them.

They have recommended the advancing of the Manufacture of Tapistry: the improving of Silk ma∣king: the propagating of Saffron: the melting of Lead-Oar with Pit-coal: the making Iron with Sea-coal: the using of the Dust of Black Lead instead of Oyl in Clocks: the making Trials on English Earths, to see if they will not yield so fine a substance as Chi∣na, for the perfecting of the Potters Art.

They have propounded, and undertaken the compa∣ring of several Soyls, and Clays, for the better making of Bricks, and Tiles: the way of turning Water into Earth: the observing of the growth of Pibbles in Waters: the making exact Experiments in the large Florentine Loadstone: the consideration of the Bo∣nonian Stone: the examining of the nature of Petri∣fying Springs: the using an Vmbrella Anchor, to stay a Ship in a storm: the way of finding the Longitude of places by the Moon: the observation of the Tides about Lundy, the Southwest of Ireland, the Bermoo∣das, and divers parts of Scotland; and in other Seas and Rivers where the ebbing and flowing is found to be irregular.

They have started, and begun to practise the pro∣pagation of Potatoes; the planting of Verjuyce Grapes in England; the Chymical examination of French, and English Wines; the gradual observation of the growth of Plants, from the first spot of life; the in∣creasing of Timber, and the planting of Fruit Trees; which they have done by spreading the Plants into many parts of the Nation, and by publishing a Page  192 large Account of the best wayes of their cultiva∣vation.

They have propounded, and attempted with great effect, the making Experiments with Tobacco oyl; the Anatomizing of all amphibious Creatures, and examining their Lungs; the observing the manner of the Circulation of the blood in Fishes; the wayes of transporting Fish from one place to another for Breed; the collecting Observations on the Plague; the examining of all the several wayes to breed Bees; the altering the taste of the Flesh of Animals, by al∣tering their food; the probability of making Wine out of Sugar-canes: Which last I will set down as one Example.