35 2 O/* Light ana Colours.

Sorts of Rays are equally reflected fromBodies, those Bodies appear white, or of

the

of which F I — 56, it is plain any other Thickness ofAir may be immediately measured thereon by means ofa Pair of Compasses, or by a parallel Ruler. Thus G i/frz 0,0000254 ; A 2 = 0,0000040 ;HK = 0,0000065 iA 6 = 0,0000119 ; HN = 0,0000194. And thus an/other Thickness for any proposed Colour or Series isevident almost by Inspection to the Ten Millionth Partof an Inch.

48. Since by Art. 19. it appears that the Thicknessesof Air and Water, exhibiting the fame Colour, are as4 to 3 ; if the Thicknesses in Air are known for theseveral Rings, you’ll have the Thickness of the Bubbleof course where the several Colours appear; and thusthe Table in Art. 27. was made. Also hence the Thick'nesses of thin Plates of Glass producing the Rings ofColours will be known, being to those of Air as 20 i031, viz. in the Proportion of the Sines of Incidentto Refraction out of Glass into Air for Yellow Light}and the Difference of the Proportion of the Sines f° rthe other Rays is not considerable.

49. These are the Measures nearly, which Sir lfa&thas express’d in the following Table, where the Num'hers are so many Millionth Parts of an Inch for th eThicknesses of the Plates of Air, Water, and Glass*which exhibit the various Colours of the several Or-ders.

Colours of theFirst Order.

Air .

Water.

Glas s ‘

"Very Black,

y

*

i

Black,

1

l x

if

Blue,

2 !

1 4

1*

{ White,

5 i

3 ?

3 f

Yellow,

7 %

5 i

4 f

Orange,

8

6

5 *

.Red,

9

61

st