At the present hour, when millions of human beings are leaving their homes in Europe, or contemplate doing so, for countries which may or may not possess a climate similar to that which gave them birth, it cannot fail to be perceived that many interesting inquiries are thereby laid open to science, on which none but the physiologist can enter with advantage. It the race of man, then, in all its varieties, affords general expression of the existing climates of the world, in reference to the circumstances which contribute to healthy organization; if one climate maintains, while another modifies more or less the characteristics of human beings, as is undoubtedly the case, it cannot be out of season to make this investigation: With what result to his own physical conformation and moral character, and more especially to that of his descendants does man, born in a congenial climate, emigrate at random into different zones? Having examined this subject in its many bearings, both by collating the written observations of travellers made cursorily without any immediate scientific object, and by questioning intelligent persons from our colonies, and other newly formed states, I premise with confidence that it is one which is most important and curious. To take a common example; - What a diversity of effects must obviously arise from one member of a family taking up his permanent abode in a portion of the American, and another in a part of the Australasian continent. Both regions afford climates which are called delightful and healthy; but their separate influence on the organization of the European is already perceptible. Indeed, it has been forcibly argued that man cannot travel out of his own zone without entailing extinction on his race. Be this as it may, an inquiry into the subject of isogenetic or congenial zones is of sufficient moment, under the existing conditions and inevitable redistribution of nations, to give basis to a branch of science; nor will it be passed over without due consideration in this series of papers.