Effects of Uniformity and Contrast on Light. 
131 
said in favour of large rooms and small window space. Moreover, light 
has a stimulating effect on the system in general, and as regards germs of 
disease, light is one of the most powerful therapeutic agents we possess. 
Germs of disease live in the dark, and to live at all, darkness is essential 
to them, whereas light destroys them. Hence w^e should build our houses 
with large windows, without black coverings, and let the sun enter the 
house irrespective of the fading of carpets. Factories should be so con- 
structed that the light can simply pour into the workrooms, with the 
avoidance of glare. For equal surface, skylights allow more light to enter 
than vertical w^indows. So-called shed roofs should, therefore, be glazed 
on the least sloping surface, whereas the reverse is invariably the case. 
For skin tuberculosis, the sun is one of the most powerful agents for cure. 
If the evil sits deeper, the application of X-rays, applied moderately, 
might produce beneficial results. At the same time, we must remember 
that X-rays are of very high frequency, and, if used excessively, might 
cause dissociation of the treated part. 
This may be explained as follows : — 
Take a substance of small atomic weight, such as Oxigon. It will 
respond or resonate with high frequencies, somewhere near the extreme 
end of the ultra-violet. If, on the other hand, we employ a heavier sub- 
stance, the frequency must decrease before a response takes place. This 
applies, for instance, to heavy carbon compounds, which respond to the 
low frequencies of the long waves between the red and the yellow. Hence 
ultra-violet rays, i.e., rays of high frequencies, must be harmful to plant 
life. The frequency is so great that the heavy groups of carbon cannot 
respond, but individual atoms may, and dissociation results. X-rays 
are even of higher frequency, and excess application must result in a 
dissociation of the treated parts. 
Sun-burning is also due to excess exposure, but the skin protects the 
parts underneath and the stimulating effect largely counterbalances the 
discomfiture. Sun-baths are, therefore, highly to be recommended if 
applied in moderation. The same thing applies to electric baths, which 
will be found invigorating if excess is avoided. 
After having dealt wdth the physiological effects of radiation, I shall 
consider how health and comfort may be obtained with artificial light. 
Uniformity is again of great importance for preserving the eyesight. 
Clusters of lamps in the middle of a room should be avoided if possible. 
The arrangement of lamps distributed over the ceiling is preferable. It 
is, however, also more expensive on account of additional wiring. The 
uniformity becomes perfect by the application of indirect light. By means 
of shades the whole light of a number of distributed lights is thrown 
against the white ceiling from which it is reflected. About half the light 
is absorbed in this way, which constitutes a waste and the reason why 
