To find the Longitude.
THis is a troublesome thing and cannot be very exactly performed, the best way is by Lunar Eclipses, for we must suppose the dist∣ance of Longitude; for Example, Between one Town and another to be the distance of their pro∣per Meridians. The better therefore to understand what distance of Longitude Rome and Paris have one from another, there ought to be observed both at Rome, and Paris, by able Astronomers, some certain part of any Lunar Eclipse; as perhaps the beginning, but rather the middle. Then the business is to know at what Hour this hapned at Rome, and at what Hour at Paris; for since the Ingress of the Moon within the shadow of the Earth appears at the same time throughout all the whole Hemisphaere, and yet the Hours differ with the Meridians, then it being found the be∣ginning of the Eclipse was at 9 of the Clock, and at Paris at 10. It must thence be concluded that Paris is distant from Rome the Longitude of 15 Meridians, as passing through 15 several De∣grees of the Aequator, there going (as before taken notice of) 15 Degrees of the Aequator to one Hour.
But to Conclude, It must be understood, that the Longitude, and Latitude which is now treated of, is that which is properly called Mun∣dane, or Geographical; for in Astronomy, as hath been already observed, the Latitude properly spoken of, is the Latitude of a Star, which is its distance from the Ecliptick, or the Arch between the Ecliptick, and the true place of the said Star: So likewise Longitude is the distance thereof from the beginning of Aries, or the Vernal Aequi∣noctial Point towards the Signs of Taurus, Cancer, and those that follow; or as some express it, an Arch of the Zodiack, drawn from the beginning of Aries through those Signs.