But this is only one of the reasons why, for health’s sake alone, it is of the first importance to give children long days in the open country. They want light, solar light, as well as air. Country people are ruddier than town folk; miners are sallow, so are the dwellers in cellars and in sunless valleys. The reason is, that, to secure the ruddy glow of perfect health, certain changes must take place in the blood – the nature of which it would take too long to explain here – and that these changes in the blood, marked by the free production of red corpuscles, appear to take place most favourably under the influence of abundant solar light. What is more, men of science are beginning to suspect that not only the coloured light rays of the solar spectrum, but the dark heat rays, and the chemical rays, minister to vitality in ways not yet fully understood.