July 9, 1891] 



NATURE 



227 



usually expected is the end of May or the beginning of 

 June. The really critical months in North- Western India 

 are August and September. If the rainfall is then 

 abundant and continuous up to the end of the third 

 week in September, with a final shower or two at the end 

 of the month, all may yet be well ; but if the rainfall of 

 these months is light and partial, and if it ceases pre- 

 maturely, the crops form no ear, and they perish and dry 

 up in the warm dry west winds that speedily follow. And 

 it is these crops that furnish the food staples of the 

 agricultural classes of India. • H. F. B. 



PHYSICAL SCIENCE FOR ARTISTS} 

 II. 

 "\X7^E next come to the absorption of light. I do not 

 * * know whether you have had any opportunity yet in 

 your laboratory course of observing the spectral pheno- 

 mena produced when white light, or say solar light, is 

 absorbed by different substances. The white light is 

 broken up by the dispersion of the prisms into a rain- 

 bow band ; while it is possible, by one means or another, 

 one substance or another, to filch out of this coloured 

 band some of the constituent colours, now at one end, 

 now at another, sometimes in different parts at once ; and 

 when this has been done, the light which finally reaches 

 the eye may be of any colour, as is evidenced by the 

 different colours you see in a stained glass window. This 

 is what happens also by the absorption of our atmo- 

 sphere, due in all probability in great part to the contained 

 aqueous vapour. The sun is white in the middle of the 

 day and red at sunset. The blue part of the light, which, 

 when all the colours reach us, looks white, has been taken 

 away, and practically nothing but red is left ; only certain 

 parts of the spectrum are left. It is easy, after two or 

 three hours' experiments with the absorption of light by 

 different media, to grasp the laws which govern sunset 

 colours precisely, as it is easy in the anatomical school 

 to study the facts relating to the human form, particular 

 muscles and the like. A diligent student will thus 

 have the world of colour at his feet. This can, 

 however, only be done by one interested in physical 

 science, and I think it should be done by anyone who 

 wishes to deal with landscapes or seascapes, anything, in 

 fact, which has to do with the natural world. The results 

 obtained in this way of course come to us pictorially, 

 chiefly in the colour of sky and water and in the colours 

 of clouds, and they are mixed up in pictures by the 

 knowledge, or want of knowledge, of the artist who 

 paints these various reflecting surfaces. The reflecting 

 surface, whether water or cloud, or what not, must not 

 only be true in colour, but perfectly formed, in order to 

 give an absolutely perfect and pleasant picture. 



Here I think it is that the need of physical science is 

 greatest, and I do not know, in fact, that there ought not 

 to be some kind of an examination in a College like this 

 which shall insure that anyone who is going to take up 

 the study of art is not colour-blind. This is done in the 

 case of sailors and engine-drivers, and I think it should 

 be done m the case of artists. There are pictures which 

 have apparently been painted by colour-blind people ; and 

 of course it should be a subject of great regret that so 

 much skill has been wasted in consequence of such a 

 malformation as this. 



It may be, of course, that in some cases, where the thing 

 may be charitably supposed to arise from a physical 

 defect, it is the result of mere ignorance, or want of observ- 

 ing power ; but if that be so, then my point is proved, 

 because it is clear that a good scientific training will cause 

 these objectionable, impossible, colours to be gradu- 

 ally eliminated from our exhibitions. On the other hand, 

 when we look at a gallery of pictures, one is so frequently 



' Continued from p. 178. 



NO. I 132, VOL. 44] 



rewarded by the exquisite truth of some of them, that 

 one could very well look over the defects of others, if 

 all thoughts of the possible progress of art achievement 

 were banished from one's mind. 



Some of you may perhaps have read Mr. Ruskin's 

 chapter on clouds. The scientific basis of the various 

 cloud forms, however, you will not find there. Now when 

 we consider that in land- and sea-scapes the sky, and 

 especially the clouds, are among the most important re- 

 flectors of light, whether white or coloured, the form of 

 the cloud is absolutely of very high importance. If the 

 light is reflected by an absolutely impossible cloud, your 

 delight at the colour, which may be true, is absolutely 

 checked by the treatment of the anatomy of the cloud. 

 Here, again, we touch a distinct branch of physical 

 science. An acquaintance with the various forms of con- 

 densation assumed by aqueous vapour under the various 

 conditions of the atmosphere would certainly keep one 

 right where one would be very apt to go wrong. I referred, 

 also, to the reflection of sunlight, whether white or 

 coloured by absorption, by water. Here, I think, is a 

 region where physical science is also helpful. There can 

 be no question that the grandest display of colour in the 

 natural world is a sunrise or sunset, either at sea, or where 

 there is a water surface to bring in a second series of re- 

 flection phenomena. As a rule, perhaps, if the water be 

 somewhat land-locked, or at all events not broken up by 

 strong wind, the effect is finer, and this perhaps is one of 

 the reasons, but only one, why the sunsets seen off the 

 west coast of Scotland are so remarkable. 



This, however, does not always hold. I have seen a 

 sunrise in the Mediterranean when passing the Straits of 

 Gibraltar twenty years ago, which was so magnificent, 

 that not only is it still present in my mind's eye, but all 

 the sailors who were swabbing the deck at the time ceased 

 work and simply gazed at it entranced. It promised to 

 be a cloudy sunrise, but suddenly the cloud pall melted 

 into mackerel sky, and the sun at rising payed out different 

 colours on the high and low patches ; the sea was 

 choppy, and every facet of every wave, and every facet of 

 a facet, being turned to different parts of the sky ; these 

 picked up and reflected to the eye different colours, so 

 that every wave looked like a casket of gems. 



The red or yellow colours on the clouds depend simply 

 upon the thickness of the atmosphere which the sunlight 

 has traversed to reach them ; the colour depends ab- 

 solutely upon the light received from the sun, and it 

 has nothing to do with the apparent angular distance 

 from the sun in your picture ; but while all this change 

 is going on in the clouds the sky itself will be zoned above 

 the horizon from the red to the blue overhead, and in 

 addition to that, you will get the greater luminosity nearer 

 the sun's place. But further than that the sky will not go, 

 because it cannot. At the same height above the horizon 

 you must have absolutely the same sky colour. Now that 

 is a very obvious conclusion. You will always note the 

 greatest possible distinction between the colour of the 

 pure sky and of the clouds. A favourite sky colour in 

 sunsets is green. I have seen no green clouds except in 

 pictures. 



I have noted a few of those pictures this year, which, in 

 my opinion, and I only give it for what it is worth, are 

 remarkable for their truth, or for the absence of it, in dif- 

 ferent degrees. The numbers are those of the Royal 

 Academy Catalogue, unless otherwise stated : — 



Clouds. — Good colour, 351, 



Good form, 288, 600. 



Good colour and form, 238. 

 Water. — Good colour, 630, 1029. 



Good surface, 682, 759, 1013. New Gallery, 102, 

 120. 



With great deference I must, until convinced to the 

 contrary, hold that much of the colour in the following 



