should fall into this Sickness.

* * * * *

Advertisement.

_Whereas 'tis taken notice of, that several persons perswade themselves,
that these_ Philosophical Transactions _are publish't by the_ Royal
Society, _notwithstanding many circumstances, to be met with in the already
publish't ones, {214} that import the contrary; The Writer thereof hath
thought fit, expresly here to declare, that that perswasion, if there be
any such indeed, is a meer mistake; and that he, upon his_ Private _account
(as a Well-wisher to the advancement of usefull knowledge, and a Furtherer
thereof by such Communications, as he is capable to furnish by that
Philosophical Correspondency, which he entertains, and hopes to enlarge)
hath begun and continues both the composure and publication thereof: Though
he denies not, but that, having the honour and advantage of being a_ Fellow
_of the said_ Society, _he inserts at times some of the Particulars that
are presented to them; to wit, such as he knows he may mention without
offending them, or transgressing their Orders; tending only to administer
occasion to others also, to consider and carry them further, or to Observe
or Experiment the like, according as the nature of such things may
require._

* * * * *

Printed with Licence for _John Martyn_, and _James Allestry_, Printers to
the Royal Society. 1666.

{215}

* * * * *

_Numb._ 13.

PHILOSOPHICAL
_TRANSACTIONS._

* * * * *

_Munday_, _June_ 4. 1666.

* * * * *

The Contents.

_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 Sc