THE MONTHLY MAGAZINE. No. XLVIII.] 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 comprebenfive Retrospect of the Progress of BRITISH LITERATURE during the laft fix Months-and similar 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 prifm, it forms a spectrum; which, Sir Ifaac Newton conceives, may be compofed of the following feven colours; viz. ft, violet; zd, indigo; 3d, blue; 4th, green; 5th, yellow; 6th, orange; 7th, red. If this fpectrum be divided into 360 equal parts, each of these 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 these 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. A circle then painted 741 indigo, 111 177 blue, 89 103 yellow, 83197 red, fhould produce white. [In future I fball not state the process for ferent colours, but merely ftate the refults, difcovering the proper proportions of the diffor the fake of brevity, and, for the fame reafon, I shall occafionally use the initial letters of the colours only.] But it is contended, that although a violet may be produced, by blending red, and indige; a green, by blending blue, and yellow; and an orange, by blending yellow, and red: yet the violet, green, and orange fo produced, are factitious and combined, and not like the violet, orange, and green, prifmatic colours, because if these 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 orange. Now Experiment A1, 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 mentioned before, (which, if it be conclufive, proves all the feven colours of the prifm to be equally elements), thefe circumstances concur in fuggefting a fuppofition; that produced by the two immediately contiguous. any factitious prifmatic colour, may be pro 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 produce the effect of the feven, or compofe white. EXPERIMENT 1. See Table, Fig. 2, A. 1. red, in white. portions, viz. Indigo.40 60 Yellow 48 Red 45 The Degrees in a Circle. 40 Blue 74 193 360 60 Yellow 193 103 Yellow 83481 Red. 360 MONTHLY MAG. No. XLVIII, Violet. See Table B 1. EXPERIMENT III. 80 or 2051 100 Violet 148 See Table B 7. From these Experiments, B 1, to B 7, it appears that a factitious colour, refembling 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 spec trum. It follows then, that any three following colours in the spectrum when combined, produce only the middle colour, because the two extremes produce only the intermediate colour. EXPERIMENT IX. 45 or 98165 80 40 30 Red Should compofe 360 163 Violet. See Table C 1. EXPERIMENT X. So or 160 Violet See Table C 6: EXPERIMENT XV. 144 27 or 63 Orange 80 152 18972 Violet Should compofe 360 732 Red. See Table C 7. From the Experiments B1 to B7, which prove that any intermediate factitious prifinatic colour, may be compofed of the two immediately contiguous, it fol lows: that if any four following colours in the spectrum be taken, a tint or fhade intermediate to the fecond and third colours will be produced. For the ift, and the 3d, produce the 2d, which is, intermediate; 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 combin ing only the 2d, and 3d, or the two intermediate colours. From the Experiments C1 to C 7, 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; avith a Indigo. quantity of the 5th colour equal to the 4th, See Table C 2. sib, and 6th, and by adding to theje the 7th Indigo colour colour in the proportion in which it exifts in the spectrum, because any three following colours produce on combination only the middle colour. On this fuppofition white is produced by EXPERIMENT XVI. See C 2. See C 5. Red 45 = Red 45 in the Spectrum. 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 r quantity to the fł, zd, and 3d; of the sth a proportion to the 4th and 6tb; and of the 6th 5th and 7th, |