The Mormon and the Mohammedan advocate polygamy. The Koran says a man must have four wives in order to always be able to find one in a good humor. There is one answer to polygamy which forever settles the question. The highest orders of animals and men are gifted by nature with an instinct prompting the union, in pairs, for life of the male and female. This instinct is located in the occipital region of the brain, and is called, in Phrenological language, Conjugality. It is large in the lion and the eagle, and in all mating birds and animals. Those animals which associate promiscuously are devoid of this sense. There is no grander example of conjugal fidelity than the eagle, the monarch of birds, building, with his consort, their rugged home on the breast of some beetling crag, and there rearing their offspring and remaining true to each other for a lifetime, and at last, when disabled by age, nourished and fed by the young birds, no doubt impelled to the filial task by respect for their magnificent virtues. If the sense of conjugality is omitted from the organization of a man or woman, they cannot be held responsible if they fail to conform to its impulses. But let every man or woman, in the possession of a complete brain, conform to the instincts of nature and emulate the virtue of the eagle. Those who practice polygamy, or who associate promiscuously, or are guilty of conjugal infidelity, are, in plain scientific language, _deficient in sense_--the sense of conjugality. It being, therefore, the law of nature that man and woman should unite in matrimony, what rule of selection may we establish which, in all cases, shall be productive of agreeable association, financial success and such physiological conditions as will result in the improvement of offspring? It has been stated that Order is Heaven's first law. With equal force it might be added that Harmony is the first law of nature. The law of Harmony pervades all nature, and men and women have long since learned to recognize it in many departments of study, inferior in dignity and importance to the topic of this lecture. As you have long studied harmony in its application to music, and colors, I introduce the study of harmony to you to-night, but it is harmony in its relation to Humanity in the law of matrimonial selection. There is harmony and discord in music; there is harmony and discord in the science of colors; and in the grand symphony of Humanity, the law is just as applicable; its obedience results in the beauty and accord of domestic felicity, its disobedience furnishes the deformity and discord of society.