Of Light and Colours.

density of Rays in the Focus is always asthe Area of the Burning-Glass diredlly , and

... 1 tl JS

dissipation, and a Force of Tension in the Solids be-y°nd what the natural State of the Body can bea 'j^rd therefore it will inevitably destroy it.

8. Whatever be the acting Principle in Freezing orCongelation, ’tis certain, the Modus Agendl , or Manner*1 Operation, must be to diminish the Velocity of thef ar ts of the congealable Substance to a proper Degree,?y which means the Fluidity will be lpst, and the Parts® e Corne rigid and fixed. Thus if the Intestine Motionthe aqueous Particles be abated by the Admixtureany extraneous Body, the Parts will be no longerbut remain to Appearance fixed in a Congelation,^ n d become a Body of Ice. Whatever this Principle°s freezing be, it i's certainly of a saline Nature, be-muse it is well known Salt will greatly increase the^°ldnefs of Water, Ice, or Snow ; and freezing Mix-Ores are always made therewith, by equal Quantities

of

e ach.

» Y- On the other Hand, fitted Bodies are rendered?oid by Heat, only by increasing the V elocity of the. ar ts ; thus Ice becomes Water, thus Metals are put"sto Fusion, and a greater Degree of If eat gives a still^atef Degree of Velocity to the Parts, and throws?etn off j n the Form of a Steam or Vapour. This^ e am or Vapour, if it consists of such Particles as willj ^it of a proper Increase of Velocity, will conceivev ery readily, apd kindle into a Flame, at the Ap r.5° a ch of a Body whose Parts are thus in Motion;at is, of fire or Flame.

There seems to be no other Difference betweenand Flame than this, that Fire consists in a glow-§ Degree of Velocity in the Parts of a Body while^ subsisting together in the Mass ; but Flame is the

Degree of Velocity in the Particles dissipated a

and

pfng off in Vapour ; or to use Sir Isaac Newton s Ex-f vision, Flame is nothing else but a red-hot Vapour.

ii. The