April I5t, 1SS7.] 



SCIENTIFIC NEWS. 



41 



scarlet cloth and a piece of violet cloth be placed side by 

 side in a good light, the scarlet will appear more orange 

 and the violet more blue than they really are. If they are 

 separated the effect is destroyed, and they appear in their 

 natural tints. Each, in fact, is changed as though it had 

 been tinged with the complementary colours of the other. 

 The result is more apparent to those who have not a well- 

 trained eye for colour, when one of the tints is grey and the 

 other a brilliant hue ; and the effect is even more striking 

 when a piece of tissue paper or muslin is laid over them. 

 A grey pattern on a green ground appears of a rose tint, 

 and the same is seen even with a black pattern. Chevreul 

 relates how one of the first paper-hanging manufacturers of 

 Paris wished to print grey patterns on grounds of apple 

 green and of rose, and that he refused to believe that his 

 colour preparer had given any grey paint to the printer 

 because the designs printed on these grounds appeared 

 coloured with the respective complementaries. He also 

 narrated that a dispute arose between certain drapers and 

 a calico-printer, to whom red, violet, and blue cloths had 

 been sent, with orders to print a black pattern thereon. 

 When they were delivered it was complained that the 

 patterns on the red cloths were of a green colour, upon 

 the violet a yellowish green, and on the blue they were of 

 a rusty brown colour, instead of black. Chevreul was able 

 to demonstrate, both by showing the patterns through holes 

 in white paper, and by cuttings of black cloth, that the 

 supposed fault was purely subjective, and that there was no 

 ground for complaint. The patterns would have appeared 

 to be more black had they been tinged with the colour of 

 the ground. The same law of contrast affects the artist, 

 and if he is forewarned may save him a considerable 

 amount of work. For example, the warm I'ght from 

 windows consisting chiefly of glass with yellow patterns 

 fills a church with a warm glow, and daylight coming in 

 through upper windows of clear glass has a bluish tint. An 

 artist who truthfully represented this on a picture and took 

 blue paint to represent the apparently blue light, will give 

 his picture an exaggerated effect. A painter generally 

 works up his picture by degrees to avoid such mistakes, 

 and where, as in water-colour painting, the sky is some- 

 times put in first, a strong colour in the landscape will spoil 

 the sky tints which have been put in, and make them 

 appear false and thin. Hence the practice of many land- 

 scape painters of covering their blank canvas with the 

 dominant tone of the scene before proceeding to finish. A 

 green background to a portrait painted in low cold tones 

 gives it a warmer tint, and the spectral redness added to the 

 greyer colour of the picture will sometimes give a singular 

 eifect, but the quality of the green is important. A 

 yellowish green, as will be seen in the diagram, will give a 

 purplish red, and a bluish green will give a more orange 

 effect. At the same time green is a difficult colour to use, 

 especially in large surfaces, unless it is considerably broken 

 up. Rosy flesh tints with grey shadows will often give 

 the shadows a greenish tinge, as already described. No 

 green exists actually, but it is not unconmion, though not 

 always pleasing, to find green paint actually used in figure 

 painting for flesh shadows; they have, of course, the reflex 

 effect of heightening somewhat the warmer colours. 



The law of contrast may be employed to determine the 

 best colour for a background for any special purpose. 

 Silver work, for example, should be displayed in such a way 

 that there should be no suspicion of orange or yellow about 

 it, since this would suggest tarnish. The opposite of yellow 

 and orange is violet and blue, and to give a spectral violet 

 or blue the rule would point out the use of a yellow or 

 orange background ; but it is necessary also to heighten the 

 whiteness of the silver, so the colour should at the same 



-time be dark. A rich brown or deep orange will, therefore, 

 have this effect. Green or red will have no ill effect, for the 

 complementary colours are purple and green. Gold, on the 

 other hand, looks well on a blue or violet ground, and would 

 be " killed " with yellow; that is to say, using the rule of 

 contrast, it would be tinged with the complementarj- to 

 yellow, namely, violet ; and violet and orange make whitish 

 pink, which would spoil the gold. A grey-green ground has 

 an excellent effect on gold. Red and gold, it is true, form a 

 rich combination pleasing to the eye; but the point here is 

 that it is somewhat to the disadvantage of the gold, as gold. 

 No one has yet succeeded in giving a definite rule or set 

 of rules for making pleasing combinations of colours, nor has 

 any satisfactory ihcoiy yet been given for showing why 

 any two colours make a pleasant or an unpleasant effect. 

 Brucke, Rood, Chevreul, Field, and Owen Jones have 

 written on the subject. It is unfortunate that many writers 

 accepted the red-yel!ow-blue theory, although this did not 

 prevent the construction of such colour diagrams as the 

 present one. Rood points out that a line drawn from violet 

 to yellow-green divides the diagram into warm colours and 

 cool colours, and he suggest that colours which are less than 

 about ninety degrees or a right angle apart, generally form 

 an unpleasant combination. Good combinations are said to 

 be always more than ninety degs. distant. Colours differing 

 by small intervals, however, often form good pairs, as yellow 

 and orange, but the reds are very apt to " swear " at each 

 other. 



EARTHQUAKES AND THEIR CAUSES. 



THE successive calamities of Krakatoa, Ischia, Granada, 

 Charleston, and now of the Riviera, have latterly 

 directed public attention, in the most painful manner, to 

 earthquakes, and to the many unsolved problems which 

 they involve. The mere surface phenomena of these, and of 

 similar events, have been dwelt upon most abundantly. 

 But concerning the causes at work, there still prevails no 

 little uncertainty. This want of exact knowledge is the 

 more to be regretted, since it affects not merely the savant 

 in his study, but the general public in its daily life. Until 

 we succeed in working out a plain, definite theory of these 

 fearful visitations, we shall never know when and where to 

 expect their approach, and can consequently neither regulate 

 our movements nor modify our domestic architecture to 

 meet the necessities of the case. 



Unfortunately, those very points which are most needed 

 for the proof or the disproof of any given theory have been, 

 until about forty years ago, overlooked as unimportant. At 

 that time Mr. Robert Mallet took up the scientific study of 

 earthquakes, to which many geologists, physicists, and 

 engineers have since made valuable contributions. Pre- 

 viously, historians, chroniclers, and philosophers had en- 

 larged on the numbers of the maimed or the slair, on the 

 overthrow of single buildings or of entire cities, and on the 

 destitution and — in too many cases — the pestilence which 

 succeeded. But they could tell us little, or nothing definite, 

 concerning the direction and the number of the shocks, or 

 their character as lateral, upwards, oscillatory, or even 

 rotatory or whirlpool-like — the most dangerous of all. 

 Another important feature is the speed at which the dis- 

 turbance is propagated, as measured by the time when a 

 shock is felt at different localiiies. This velocity has on 

 different occasions been estimated at from 2,000 to 12,000 

 feet per second, according to the character of the strata 

 traversed. In certain cases a _^shock may be propagated 

 through the soil more rapidly than sound can traverse the 

 air. Thus, in the great gun-cotton explosion at Stowmarket, 

 in August, 187 1, the windows of buildings situated about 



