124

Of Optics.

ferment in the stomacb, otherwise, an apple would be immediate deatbto him who eats it.

The mixing of forne fubstances with others, will releafe the air fromthem, all of a sudden, which may be attended with very great danger..Of this we have a remarkable instance in an experiment made by Dr.Slare ; who having put half a dram of oil of carraway-feeds into oneglass, and a dram of compound spirit of nitre in another, covered themboth on the air-punip with a receiver fix inches wide, and eight inchesdeep, and then exhausted the air, and continued pumping until all thatcould poffibly be gpt both out of the receiver, and out of the twofluids, was extricated.: then, by a particular contrivanee from the topof the receiver, he mixed the fluids together; upon which, they pro-duced such a prodigious quantity of air, as instantly blew up the re-ceiver, although it was prefled down by the atmofphere with upwardsof 400 pound weight.

L E C T. VIIL

Of optica

L IGHT consists of an inconceivably great n umher of particles flow-ing from a luminous body in all manner of directions; and thefeparticles are fo small, as to furpass all. human comprehension.

That the number of particles of light is inconceivably great, appearsfrom the light of a candle - r which, if there be no obstacle in the wayto obstruct the pastage of its rays, will fili all the fpace within twomiles of the candle every way with luminous particles, before it haslost the least sensible part of its substance.

A ray of light is a continued stream of these particles, flowing fromany visible body in a straight line : and that the particles themselves areincomprehensibly fmall, is manifest from the following experiment.Make a fmall pin-hole in a piece of black paper, and hold the paperupright on a table facing a row of candles standing by one another ;then place a fheet of pasteboard at a little distance behind the paper,and forne of the rays which flow from ali the candles through the holeThe amazing in the paper, will form as many fpecks of light on the pasteboard, asthff^a-ticks khere are candles on the table before the piate : each fpeck being asof iight! C 65 distinct and ciear, as if there was only one fpeck from one single can-dle : which fhews, that the particles of light are exceedingly fmall,otherwife they could not pafs through the. hole from fo many different2 candles