of Edinburgh, Session 1866 - 67 . 5 
heat of the tropics, he cannot call into exercise his highest powers. 
The calorific rays are all-powerful there, and lassitude of body and 
immaturity of mind are their necessary results ; while in the dark- 
ness of the polar regions, the distinctive characters of our species 
almost disappear in the absence of those genial influences which 
are so powerful in the organic world. 
It is well known to all who seek for health in a southern climate, 
that an ample share of light is considered necessary for its re- 
covery. In the hotels of France and Italy, the apartments with 
a south exposure are earnestly sought for, and, under the advice 
of his physican, the patient strives to fix himself in these bright 
localities. The salutary effect, however, thus ascribed to light is 
supposed to arise from the greater warmth of the solar rays ; but 
this can hardly be the case in mild climates, or indeed in any climate 
where a fixed artificial temperature can be easily maintained. 
Something, too, is due to the cheering effect of light upon an 
invalid ; but this influence is not excluded from apartments so 
situated that from a western or even northern window we may enjoy 
the finest scenery illuminated by the full blaze of a meridian sun. 
While our distinguished countryman, Sir James Wylie, late 
physician to the Emperor of Russia, resided in St Petersburg, he 
studied the effects of light as a curative agent. In the hospitals of 
that city there were apartments without light, and upon comparing 
the number of patients who left these apartments cured, he found 
that they were only one-fourth the number of those who went out 
cured from properly lighted rooms. In this case the curative 
agency could not reasonably be ascribed either to the superior 
warmth or ventilation of the well-lighted rooms, because in all 
such hospitals the introduction of fresh air is a special object of 
attention, and the heating of wards without windows is not diffi- 
cult to accomplish. 
But though the records of our great hospitals may not assist us 
in our present inquiry, yet facts sufficiently authentic may be 
gathered from various quarters. In the years of cholera, when this 
frightful disease nearly decimated iiie population of some of the 
principal cities in the world, it was invariably found that the 
deaths were more numerous in narrow streets and northern ex- 
posures, where the salutary beams of light and actinism had sel- 
