( 4 ° 5 )

i. Find the Parallax of Jupiters Orb to the Time proposed, and note whc-ther it be to be Addedor Substracted.

z. Extend the Thread from the Center of the Instrument over the Parallaxnumbred in the sinall Arch, it cuts oft in the four divided Circles, so manyhours as each Satellite spends in paiiing from the Axis of the Shadow to theAxis of ¥ viewed from our Earth ; thele I call the Simple Parallacticl <. Inter-vall, which if the Parallax was to be added, are also Additional, if to besobstracted, Subductive.

3. To these Parallattick. Tntcrvals add the Times of half the Duration ofthe Eclipfe of each Satellite, which for the First may beastumed i^ 1 io 1 forthe zd, ih 30', ( greater exactness being needleß ) ; but for the 3-/, and4 tb when Eclipfed, (their Immerfions into the Shadow and Emerfion from itbeing commonly given in the Catalogues ) take half. the Difference of theseTimes at the next Eclipfe, to the Time proposed, for the half Duration, andAdd them to the Simple Parallailick,. Intervall, so have you them Augmcnted.-But as often as the 4^ Satellite is not Eclipfed, ( which is two Years in everysix ) its Interval nteds no Augmentation.

4. Find in the Tables the Times of the Eclipses of each Satellite next pre-ceedihg the Time proposed, and when the 4 tb is not Eclipfed, of its paiiing,the Axis of the Shadow, to which ifi the ParallaRick. Intervall Augmentedwere Additional, Add ehern to, if Subductive, Subttract them from, eachthe Time of its proper Satellite' s Eclipfe, so have you vey near the ApparentTimes when each Satellite last past over the Axis of if, viewed from ourEarth.

5. Substract each of the Times thus got from the Time proposed, the Re-mainders are the Intervals of the Motion of each Satellite from ¥’* Axis.

6. Extend the Thread, from the Center over each of these Intervals of Mo-tion numbred feverally in the divided Circles belonging each to its proper Sa-tellite, where it cuts the proper Orbit of that Satellite, whose Interval was :numbred in its peculiar Circle, it fhews amongst 1 the Parallels, how manySemidiameters of If, that Satellite is distant from him, and on which fide ofhim ’tis Posited.

Note further, that the Thread as it lay extended over the Parallax of theOrb numbred in the small Arch, where it cut the ßveral proper Orbits ofeach Satellite, flicwed amongst the Parallels, how many Semidiamerers of ¥*,the Center of the Shadow was distant from the Center of ¥, viewed from -our Earth. And that if the Parallax of the Oib were Additional, the Sha-dow lies on the Right-hand from ¥, if Subductive on the Lest.

To explain these Precepts, I fhall give two brief Examples. Let it bethen proposed to know how far each Satellite appears distant from V* on thez6 cil of Dec. this present Year 1685. at 6h 52/. p. m. when the T bird Sa-tellite falls into the Shadow y also on Jul. 16. 16S6. at ick - co 7 . p. m. when >there is no Eclipfe. -

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