Page:Philosophical Transactions - Volume 001.djvu/405

(389) Partial Eclipses, the Beginning and End, and in Total ones of short continuance in the Shadow, the Beginning and End of Total darkness, are unfit for nice Observations, by reason of the slow change of Apparences, which the Oblique Motion of the Shadow then causeth. For these reasons I shall propound a Method peculiarly design'd for the Accomplishment of the Geographical end in Observing Lunar Eclipses, free (as far as is possible) from all the mentioned Inconveniences.

For, First, It shall not be practicable without a Telescope. Secondly, The Observer shall alwayes have opportunity before his principal Observation, to note the Distinction between the True Shadow and the Penumbra. And, Thirdly, It shall be applicable to those Seasons of the Eclipse, when there is the suddenest Alteration in the Apparences.

To satisfie all which intents,

Let there be of the Eminentest Spots, dispersed over all Quarters of the Moons Surface, a select number generally agreed on, to be constantly made use of to this purpose, in all parts of the World, As, or Example, those, which M. Hevelius calleth,

Let in each Eclipse, not all, but (for instance) three of these Spots, which then lie nearest to the Ecliptick, be exactly observed, when they are first touch'd by the True Shadow, and again, when they are just compleatly entred into it, and (if you please) also in the Decrease of the Eclipse, when they are first fully clear from the True Shadow: For the accurate determinations of which moments of time (that being in this business of main importance) let there be taken Altitudes of remarkable Fixed Stars; on this side