Shading the glass with canvas or washes during the summer months has the same object in view.
The amount of want of illumination in each portion of the penumbra is roughly indicated by the shading.
Broadly speaking it may be said that a distinction may be drawn between " spirits " and " gods," but it is a distinction of degree rather than of kind, obvious enough at the upper end, yet shading off into manifold varieties of resemblance in the lower forms. Some writers only recognize friendly agencies as gods; but destructive powers like the volcano, or the lords of the underworld, cannot be regarded as the protectors of the life of man, yet they seem in many mythologies to attain the full personalised stature of gods with definite names.
They do not need shading, but should have plenty of air, and be syringed daily in the afternoon.