40 



SCIENTIFIC NEV\^S. 



[April 1st, 1887. 



no ingenuity can pass ? " As no " talented correspondent " 

 came forward to answer this question, we will, after this 

 lapse of fifty years, tal;e on ourselves to do so. On a 

 bicycle, one mile has been ridden in a trifle less than two 

 minutes and forty seconds, and five miles have been 

 covered in fourteen minutes and twenty-two seconds. Fifty 

 miles have been covered in two hours forty-seven minutes 

 and thirty-six seconds. Within the space of a single day 

 (24 hours) one rider urged his machine over 295 miles of 

 road. Turning to tricj'cles we find that fifty miles have 

 been ridden on the high road in three hours and nine 

 minutes, and one hundred miles in a little under eight 

 hours and a half. These, we believe, are not the best 

 records in cycle riding, but they will serve to answer 

 " Constant Reader's " inquiry. Let us hope he is not 

 beyond the possibility of profiting by our replies. 



With these few figures we may fittingly conclude ; for 

 perhaps nothing could be produced to illustrate the progress 

 of industrial science more conclusively than the modern 

 cycle. 



NOTES ON COLOUR. 



II. 



THERE is a popular idea that " complementary" colours 

 are to be explained by the red-blue-yellow theory, 

 •which contains an error already pointed out in the first 

 series of these notes. It is said that red is a complementary 

 colour to green, because green is a mixture of the other two 

 colours; and blue is complementary to orange, because 

 orange is a mixture of yellow and red. 



This ingenious idea has doubtless been of as good 

 service to those whose business hes in the use and arrange- 

 ment of colours, as the still prevalent three-colour theory 

 alluded to above ; and each has the merit of leading to 

 tolerably correct results up to a certain point. 



The true definition is that two colours are said to be com- 

 plementary when the result of their mixture is white. To 

 mix paints is, as was described last month, merely to 

 subtract the colours, the resulting tint being produced by the 

 survival of those which the paints have in common. One of 

 the simplest methods, and one to which accurate measure- 

 ments can be readily applied, is that of revolving discs. 

 Two or more colours can be combined in any desired pro- 

 portions by painting cardboard discs, which are slit 

 radially from the centre to the circumference, so that they 

 can be mounted on the same axis, and then set in rapid 

 rotation. A drill, provided with a pair of bevel wheels, 

 which can be obtained for a shilling or two, is very con- 

 venient for this purpose. Discs painted with gamboge and 

 cobalt will give a pure white when mixed in the proper 

 proportion. Many painls, on account of their impurity, will 

 at the most give a neutral grey. 



The study of many colour problems is facilitated by the 

 use of colour diagrams or charts. The diagram given here 

 would, if coloured, exhibit all tints except those containing 

 grey. 



The strong circles enclose the pure simple colours — violet, 

 ultramarine, blue, peacock blue, sea-green, green, yellow 

 green, yellow, orange yellow, orange, vermilion, red, purple. 

 The complementary colours are diametrically opposite, and 

 white is at the centre. An inner circle contains tints which 

 are mixtures with white — lilac, turquoise, pale green and 

 yellow, and pink. The outer circle shows mixtures with 

 black. The blues and greens when mixed with black do 

 not alter their nature much, but appear darker; indigo is 

 identical with a mixture of Prussian blue and black. The 

 greens do not much alter their nature, but may be described 

 as dark green. True sage green contains white as well as 



black, and should not appear in this diagram. Yellow with 

 black gives olive, and orange and red give the various 

 browns. A more complete chart might be arranged by 

 taking the circle of pure colours and their mixtures with 

 white, and a series of similar diagrams, each containing an 

 additional quantity of black, and piling these on the top of 

 each other, forming a column ; or successive leaves to a 

 book. The centre of this column would contain all the pure 

 greys, ending with white at the top and black at the bottom. 

 The pure browns would be directly under the pure orange 

 and red, while coffee colour, which is whitish, would be 

 nearer the centre. 



The diagram has other uses than the indication of the 

 complementary colours. The three colours of Young's 

 theory may be represented on it at the corners of a triangle, 

 as has been done in what is known as Maxwell's diagram. 

 Neglecting the two outer circles, which are given merely 

 for the purpose of showing the browns and other combina- 

 tions with black, the result of any mixture of two or more 

 colours will be found at a point between them, whose dis- 

 tance from the colours depends on the proportion in which 

 they are mixed. For example, equal parts of vermihon and 

 emerald green give a pale yellow, and a mixture of ver- 



milion and ultramarine gives lilac, and violet with sea-green 

 gives pale blue ; while violet, orange, and sea-green to- 

 gether will make a light pink. These mixtures are at once 

 accounted for by the theory of the three sets of nerves or 

 processes of sensation. 



The true mixture of colours, as distinguished from the 

 mixing of paints is a matter of importance in textile manu- 

 factures composed of coloured threads. The result of a 

 number of parallel threads, seen at a distance, is a true 

 mixture of their colours. The effects were studied by 

 Chevreul, when he was appointed director of the Gobelins 

 Dye Works. The colours were not generally brilliant 

 enough to produce white, but a mixture of complementary 

 tints gave greJ^ The beautiful grey tints of a distant land- 

 scape are due to the mixing of innumerable colours, and the 

 pearly effect of a Cashmere shawl is greatly due to the small 

 points of bright colours, which produce a richer appearance 

 than a simple tint of grey, because, except at a considerable 

 distance, the mixture is not quite complete. 



Another use to which the colour chart may be put is to 

 predict the effect of the contrast of colours. If a piece of 



