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Of Light and Colours.

J a Lens or Burning-Glass , they becomenr dent, and burn with an Intensity propor-tional

fanner as rubbing a black Piece of Cloth, which has

j, Utl g in she Sun to dry, will cause it to throw out theguides of Light which it had imbibed from the Sun ;

J^reas a white Piece of Cloth, which reflects most of*5 Sun’s .Rays, emits no such lucid Sparks in the Dark.of ari y other Reasons might be urged to strew that Lighta every Kind is owing to one and the fame Cause inheater or lesser Degree, viz. to the Velocity of the' ay "tf of the lucid Body ..

,j 4 - It has been justly observed by some of our mo-'nlf Philosophers, that aBual or absolute Heat is to sen-f e or relative Heat the same as Motion is to Velocity ;j? r absolute Heat is nothing but the whole Motion of allV Parts of the ignited Body, and sensible or relatkesat respects only the comparative Velocity of the Parts.j^Vs equal Bulks of Mercury and Water set in a Sand-^t, where the Heat of the Fire may be uniformlyjjMnunicated to both, will acquire in equal times equalfyStees of absolute Heat, but the relative Heat of then e 3ter ’ or that which is sensible to the Finger, will be,. n ar 14 times as great as that of the Mercury : because

k. ^ Water having 14 times a less Quantity of Matter,

1 * admit of Velocity so much in Proportion greater.

] 5 . Again, if Mercury and Water have the fame re-f ? e or sensible Heat, that is, if both are heated inR" a Manner as to cause an equal Ascent in thej 'sonometer ; then a Quantity of Mercury will heatfy Times as much Water as the fame Quantity ofc Q i a . te r will do ; or it will make the lame Quantity ofli ^ Water 14 times hotter than the fame Quantity ofp e . Water can, All which is easy to be shewn by Ex-^"tient, and abundantly proves the Truth of the fore-^8 Theory, viz. That Heat and Fire are wholly ow-ls to ’.’ ~ ...

his 0 the Velocity of the parts of the heated or ardent

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F ' The various Phænomena of He< ‘ and Cold , Fire,S»c. aye rationally accounted for on this Thc-

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