June 25, 1891] 



NATURE 



177 



that is to say, in a sun-setting or moon-setting, if you 

 paint an unbroken sky, there must be an increase of 

 intensity towards the light source. I am almost ashamed 

 to make such a statement, because it is so obvious to you 

 as students of science, but to the artist who is not a very 

 strict observer, why should it strike him ? The fact 

 remains that it has not struck a great many artists. If 

 you study the pictures Nos. 650, 989, 1144, in the Royal 

 Academy, and No. 39 in the New Gallery, you will find 

 there indications of a neglect of this law. Now the sky is 

 far more luminous than it ought to be by the light indi- 

 cated by the landscape. Again, the setting sun is not so 

 bright as the clouds which it is supposed to illuminate, 

 and in some cases there is absolutely no grazing reflec- 

 tion indicated, and, if anything, the sky is rather less 

 luminous where the sun is than further away ! 



A good rule, and one which a student of physical 

 science would be certain to act upon with considerable 

 care, would be never to show anything as reflected which 

 was not there. 



An interesting example of this kind was exhibited in 

 the Academy some years ago. It so happened that a 

 French man of science wrote a book on physical pheno- 

 mena, beautifully illustrated. Among the illustrations 

 was a coloured copy of a photograph of a soap bubble. 

 Now the laboratory in the College de France, in which the 

 photograph was taken, was, like yours, ver^well lighted 

 by many windows, and the soap bubble was. blown in the 

 middle of it. A translation of this book appeared in 

 English, and the illustrations were reproduced. 



An artist had a most excellent idea. He thought he 

 would paint a picture of a garden, which he did admir- 

 ably. The foreground looked bare, so he thought he 

 would put children playing in it. It next struck him, 

 apparently, that the children did not seem to be quite 

 sufficiently occupied, so he painted one blowing soap 

 bubbles. But, alas ! less fortunate than you, the artist 

 had no laboratory in which he could blow and study soap 

 bubbles for himself; so what did he do '^. He copied the 

 bubble which was riddled with windows, although there 

 were no windows in the garden. He thought that the 

 nature of bubbles was windowy. 



Then, again, in the matter of reflection, it would not 

 be right that I should fail to remind you that, besides 

 things terrestrial, we have the moon, which rules the 

 night, and rules the night because it reflects the sunlight 

 to us. Now, in a little talk like this I must not take up 

 much time with astronomy, but it is fortunate that books 

 on astronomy can be got for dd. or \s. which will tell us, 

 say, in half an hour, the chief points about the moon 

 which we need consider in the present connection. The 

 moon is lighted by the sun. The sun can only light one 

 half at a time. If we are on the side of the moon which 

 is lighted by the sun, we must see the complete lighted 

 half which we call a full moon. If we see a full moon, 

 we must have our back to the sun. When the position of 

 the moon with reference to the earth is such that we can 

 see half the lighted portion of the moon, we generally find 

 that the part of the moon which is turned to the sun is 

 lighted up. 



But none of these things are so in art. Last year a 

 picture in the Academy was absolutely disfigured by the 

 dark part of the moon being turned to the sun. Surely 

 it was not worth the artist's while to paint a moon if he 

 did not know how to do it. But the moon has been 

 treated, if possible, worse than that. Some years ago a 

 friend who knew I was interested in astronomy had 

 another friend who had painted a picture, and he wished 

 me to look at it to see if the moon was right. I went and 

 saw the picture, and had to say that the moon was 

 wrong. It was perfectly clear that the picture was 

 intended to represent the sun setting on the right, beyond 

 the part of the 1 indscape included in the picture, so that 

 the moon rising on the left, and shown in the picture, 



NO. I 1 10, VOL. 44] 



must be full. My friend said to me he knew this, 

 and that as a matter of fact the artist had painted 

 a full moon to start with, but he had altered it be- 

 cause it " destroyed the balance of his picture." That 

 you see was where art came in. And then he added 

 that the painter was not satisfied with the moon as it 

 stood ! I told my friend to say that I regretted that the 

 full moon destroyed the balance of the picture, and that 

 even a delicate crescent did not make things quite right, 

 and I suggested that the effect of two or even three 

 moons, of different sizes if needs be, should be tried. 

 The artist said that this was nonsense ; I replied that 

 I did not consider it greater nonsense than the moon as 

 he had represented it, and so the matter ended. 



I am sure that the students of this College will know 

 that such things as these are to be avoided, even if there 

 were difficulties caused by the non-existence of a book 

 on astronomy. No artist need paint a moon in a picture 

 if he be too ignorant to paint it properly. 



Everything that you paint in a picture, which you paint 

 because it reflects light, should be painted its proper size 

 in relation to the other objects. It seems, however, that 

 the moment a body which reflects light does not happen 

 to be on the surface of the earth, you may, in art, make 

 it as large as you please. I do not think that the moon's 

 distance from the earth gives us any right to treat it in 

 this way. 



An eminent American astronomer some years ago 

 looked at the pictures in the New York galleries from 

 this point of view. The moon subtends a certain angle. 

 Everything else in a picture can be expressed in this 

 way the moment you put a moon into it. This astronomer 

 took the trouble to get out a statistical table of the heights 

 of the different mountains and hills as drawn by American 

 artists in pictures of places taken from other places (the 

 distances being therefore known) with a moon thrown in. 

 The maximum height was 105 miles, and the lowest 13 ! 



Next, permit me to say a few words on another point, 

 in order to show that the student of art will delight more 

 and more in his work as he or she knows more and more of 

 physical science. I now take refraction. You know that 

 refraction can be divided into deviation and dispersion. 

 The phenomena of deviation teach us that when a beam 

 of light, whatever its colour, passes out of one medium 

 into another its course is changed. An experiment, which 

 is easily performed and which is more a home experiment 

 than a laboratory one, is to put a coin into a basin and 

 look over the edge in such a direction that the coin is 

 just invisible : then fill it with water, the coin appears. 

 Another experiment is to insert a straight body, such as 

 a pencil, into this bowl of water : it appears to be broken ; 

 refraction, then, appears to make water shallower than it 

 really is. If you look at 1094, you will find that this 

 deviation has been made to act the wrong way. 



It is rather a bad thing to attempt to paint a nymph 

 partly in and partly out of dear water, because her body, 

 if the picture be truly painted, would follow suit with the 

 pencil. 



Passing from deviation to dispersion we come to rain- 

 bows. You have learned, and perhaps seen demonstrated 

 by experiment, that we deal with a beam of white light 

 coming from the sun and refracted at the front surface of 

 a rain-drop. It is next reflected and again refracted 

 down to the eye, so that the eye sees a bow, with all the 

 spectrum colours due to the dispersion. If the light be 

 strong enough, we get what is called a supplementary 

 bow, and, in consequence of internal reflections, the two 

 reds are brought together. 



The point is that in this dispersion, brought about by the 

 rain-drops, the effect is produced in a plane passing 

 through the sun, your eye, and the rain-drop ; your eye 

 being in the centre, so that if you see a rainbow at all, 

 you must have your back to the sun. The bow is always 

 circular, and high or low according to the height of the 



