h requisite, and that with very little or no trouble in fitting the
_Engine_, and without much skill in the _Grinder_. He thinks it very exact,
because to the very last stroke the Glass does regulate and rectifie the
_Tool_ to its exact Figure; and the longer or more the _Tool_ and _Glass_
are wrought together, the more exact will both of them be of the desired
Figure. He affirms further, that the motions of the Glass and Tool do so
cross each other, that there is not one point of eithers surface, but hath
thousands of cross motions thwarting it, so that there can be no kind of
_Rings_ or _Gutters_ made, either in the _Tool_ or _Glass_.

5. A _New Instrument_, by which the _Refraction_ of all kinds of Liquors
may be exactly measured, thereby to give the Curious an opportunity of
making Trials of that kind, to establish the _Laws_ of _Refraction_, to
wit, whether the _Sines of the Angles of Refraction are respectively
proportionable to the Sines of the Angles of Incidence:_ This Instrument
being very proper to examine very accurately, and with little trouble, and
in small quantities, the _Refraction_ of any Liquor, not only for _one_
inclination, but for _all_; whereby he is enabled to make accurate
_Tables_. By the same also he affirms to have found it true, that what
_proportion_ the _Sine_ of the Angle of the one _inclination_ has to the
_Sine_ of its Angle of _Refraction_, correspondent to it, the same
proportion have all the other _Sines_ of Inclination to their respective
_Sines_ of _Refractions_.

Lastly, this Author despairs not that there may be found many Mechanical
Inventions, to improve our Senses of _Hearing, Smelling, Tasting,
Touching_, as well as we have improved that of _Seeing_ by _Optick
Glasses_.

* * * * *

London, Printed with Licence for _John Martyn_, and _James Allestry_,
Printers to the _Royal Society_.

{33}

* * * * *

_Numb._ 3.

PHILOSOPHICAL
_TRANSACTIONS._

* * * * *

_Munday_, _May_ 8. 1665.

* * * * *

The Contents.

_Some Observations and Experiments upon _May-dew_. The Motion of the
_Second Comet_ predicted, by the same person, who predicted that of the
former. A Relation of the Advice, given by a _French_ Gentleman,
touching the Conjunction of the _Ocean_ and the _Mediterranean_. Of the
way of killing _Ratle-snakes_,