Page:History of the Royal Society.djvu/205

 surface of the Moon: And lastly, because in small 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 Appearances, which the oblique Motion of the Shadow then causeth: For these Reasons I shall propound a Method particularly designed 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 always have Opportunity, before his principal Observation, to note the Distinction between the true Shadow and Penumbra.

Thirdly, It shall be applicable to those Seasons of the Eclipse, when there is the suddenest Alteration in the Appearances. To satisfy all which Intents,

Let there be of the eminentest Spots, dispersed over all Quarters of the Moon's surface, a select Number generally agreed on, to be constantly made use of to this Purpose, in all Parts of the World: As for Example, those which Hevelius calleth

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