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MONTHLY

No. XLVIII.]

MAGAZINE.

C

AUGUST 1, 1799. [No. 1. of VOL. VIII.

On the 20th day of July was published, the SUPPLEMENTARY NUMBER to the Seventh Volume of the MONTHLY MAGAZINE, containing-A comprehenfive Retrospect of the Progress of BRITISH LITERATURE during the last fix Months-and fimilar, Retrospects of GERMAN, FRENCH, and SPANISH LITERATURE; with INDEXES, TITLE, &C.

ORIGINAL COMMUNICATIONS.

For the Monthly Magazine. EXPERIMENTS ON COLOURS.

Fa ray of light pafs through a glafs I prima, it forms a fpectrum, which, Sir Ifaac Newton conceives, may be compofed of the following feven colours; viz. ft, violet; 2d, indigo; 3d, blue; 4th, green; 5th, yellow; 6th, orange; 7th, red. If this fpectrum be divided into 360 equal parts, each of thefe colours (according to Sir Ifaac Newton) will occupy that proportion of parts which is affigned to it in the circular spectrum. See Fig. 1. And if thefe colours be mixed, by making the circle revolve fwiftly round its centre, they compofe white.

It is generally known that indigo and red, when mixed in proper proportions, produce violet; that blue, and yellow, produce green; and that yellow, and red, produce orange.

Does it not then feem probable, fince indigo, blue, yellow, and red, are capable of producing the other three colours, viz. violet, green, and orange, that indigo, blue, yellow and red, may be the only original, or elementary colours, at least that, if mixed in due proportions, they should pro duce the effect of the seven, or compofe white.

193

A tircle then painted 74 11 indigo, 111 177 blue, 89 193 yellow, 83 18+ red, fhould produce white.

193

[In future I fhall not ftate the process for difcovering the proper proportions of the different colours, but merely flate the refults, for the fake of brevity, and, for the fame reafon, I fhall occafionally ufe the initial letters of the colours only. ]··

But it is contended, that although a violet may be produced, by blending red, and indigo; a green, by blending blue, and yellow; and an orange, by blending yellow, and red yet the violet, green, and orange for produced, are factitious and combined, and not like the violet, orange, and green, prifmatic colours, because if thele colours, fo compofed, be paffed through a fecond prifm, they will be feparated into the two elementary colours compofing

them;.

.which, it is faid, cannot be done with the prifmatic violet, green, and oranges Now Experiment Ar, and the confideration, that the factitious violet, green, and orange, are each compofed of the colours immediately contiguous to them the one to the right hand, and the other to the left hand, in the prifmatic fpectrum; as well as the objection nontioned before, (which, if it be conclufive, proves all the feven colours of the prifm to be equally elements), thefe circumstances concur..in .fuggetting a fuppofition; that produced by the tayo immediately contiguous. any factitious prifmatic colour, may be pro

EXPERIMENT 1. See Table, Fig.2, A. 1.

red, in white.

To afcertain upon this fuppofition the proportion of indigo, blue, yellow, and See the spectrum for the following portions, viz. Indigo 40 Blue

60

Yellow 48 Red 45

The Degrees

The Colours

in the Spec

trum.

Indigo.

Coloursinthe
Circle which

is to curtain

the four

Jours.

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89 193

Red

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103 Yellow

360

MONTHLY MAG. No. XLVI.

85

Violet.

See Table B 1.

EXPERIMENT HI
100 Violet
740

to or 205-4

60.

154

Should compofe 360

3 W

42 Blue

Indigo.
See Table B 2.

EXPERIA

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Red. See Table B 7. From thefe Experiments, B1, to B:7, it appears that a factitious colour, refem. bling any colour in the prifm, may be produced by the combination of the two that are immediately contiguous, in the proportion in which they are in the fpec

trum.

It follows then, that any three following tolours in the spectrum when combined, produce only the middle colour, becaufe the two extremes produce only the interme

diate colour.

EXPERIMENT IX. 45 or 98 Red

30

90 Violet

80 174165
87 45 Indigo
165

40

Should compofe 360

Violet.

See Table C 1.

EXPERIMENT X.

80 or 160

Violet

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Indigo

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Blue

Should compofe 360

XIV.
Yellow

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From the Experiments B1 to B 7,. which prove that any intermediate factitious prifmatic colour, may be composed of the two immediately contiguous, it follows: that if any four following colours in the spectrum be taken, a tint or hade intermediate to the fecond and third colours will be produced. For the 1ft, and the 3d, produce the zd, which is interinediate ; and the 2d, and 4th, produce the 3d, which is intermediate to them; confequently the tint, fhade, or colour, produced by all the four, will be the fame, as would have been produced by combining only the 2d, and 3d, or the two intermediate colours.

From the Experiments C1 to C7, it may be inferred, that white or the fame effect which is produced by the combination of the feven colours, will be produced by beginning with any colour in the spectrum, and combining a quantity of the 2d colour equal to theft, ad, and third; with a Indigo. quantity of the 5th colour equal to the 4th, See Table C 2. 5th, and 6th, and by adding to thefe the 7th

colour

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colour in the proportion in which it exists in the spectrum, because any three following colours produce on combination only the middle colour. On this fuppofition white is produced by

EXPERIMENT XVI.

Violet 80 + Indigo 40+ Blue 60,

Green 60+ Yellow 48 + Orange 27.
Red 45 in the Spectrum..

See C 2,
See C 5.
CS

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It follows from what has preceded, that the following combination of colours will produce white; viz. begin at any colour in the spectrum, and take of the ad a proportion or quantity: to the 1ft, 2d, and 3d; of the 5th a proportion to the 4th and 6tb3 and of the 6th 5th and 7th.

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From the circumstance, that if four following colours be taken, a fhade intermediate to the 2d and 3d, will be produced; it is evident, that white shoul be produced by that shade, or tint, equal in quantity to the 1ft, 2d, 3d, and 4th colours, combined with the 6th colour, equal in quantity to the 5th, 6th, and 7th. By this method white may be produced by the combination of two colours, or rather by one prifmatic colour, and a shade intermediate to two others, which fhade may be diftinguished by a name compounded of the two colours, to which it is intermediate.

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