_Certain _Problems_ touching some Points of Navigation: Of a new Contrivance of _Wheel-Barometer_, much easier to be prepar'd, than others. An account of _Four Suns_ which lately appear'd in _France_; and of two, unusually posited, _Rainbows_, seen in the same Kingdom. A Relation of an Accident, by Thunder and Lightning, in _Oxford_. An Experiment, to examine, what _Figure_ or Celerity of Motion begetteth or increaseth _Light_ and _Flame_. Some Considerations touching a Letter in the _Journal des Scavans_ of _May__ 24. 1666. * * * * * _Certain _Problems_ touching some Points of _Navigation_._ These _Problems_ are presented by the Learned and Industrious _Nicolaus Mercator_, for the advancing of that Excellent and Beneficial Science, _Navigation_, as follows: The line of _Artificial Tangents_, or the _Logarithmical Tangent-line_, beginning at 45 deg. and taking every half _degree_ for a whole one, is found to agree pretty near with the _Meridian-line_ of the _Sea-Charte_; they both growing, as it were, after the same Proportion. But the Table of _Meridional_ degrees being calculated only to every _Sexagesimal_ minute of a degree, shews some small difference from the said _Logarithmical Tangent-line_. Hence it may be doubted, whether that difference do not arise from that little errour, which is committed by calculating the Table of _Meridional_ degrees _only_ to every minute. {216} Mr. _Oughtred_ in the VI. _Chap._ of his _Navigation_, annexed to the Book, entituled, _The Circles of Proportion, and the Horizontal Instrument_ &c. mentions an Artifice, by himself discover'd, by which it may be effected, that the small Parts of the _Meridian_ be not _one_ minute (which on the face of the _Earth_ answers to above an _English_ Mile) but the hundred-thousanth, or, if need be, the millioneth part of a minute, scarce exceeding one fifteenth part of an Inch: Which thing, _he saith_, he is able to perform in _Tables_ unto the _Radius_ 10000000; yet nothing at all differing either in their form or manner of working from those that are now commonly in use. But which way this is to be done, this _Author_ hath not made known to the Publick. And, though such _Tables_ unto the _Radius_ 10000000, had been brought to light, yet would they not be sufficient to prove the identity or sameness of the said two Lines, as to continue the comparison between them as far, as the one of them, _videl._ the _Logarithmicall Tangent-line_, is already calculated, that is; to Ten places, besides the _Charactoristick_.