He was an indefatigable worker in the museum of the Bombay Natural History Society, which he helped to found, and many of his papers and notes are preserved for us in the pages of its excellent _Journal_, of which he was an original joint-editor. He was for long secretary of the Insect Section, and then president. Before his retirement he was elected one of the Vice-Presidents of the Society. Mr. Aitken was a deeply religious man, and was for some twenty years an elder in the congregation of the United Free Church of Scotland in Bombay. He was for some years Superintendent of the Sunday School in connection with this congregation, and a member of the Committee of the Bombay Scottish Orphanage and the Scottish High Schools. His former minister says of him, "He was deeply interested in theology, and remained wonderfully orthodox in spite of" (or, as the present writer would prefer to say, _because of_) "his scientific knowledge. He always thought that the evidence for the doctrine of evolution had been pressed for more than it was worth, and he had many criticisms to make upon the Higher Critics of the Bible. Many a discussion we had, in which, against me, he took the conservative side." He lets one see very clearly into the workings of his mind in this direction in what is perhaps the finest, although the least well known of his books, _The Five Windows of the Soul_ (John Murray), in which he discourses in his own inimitable way of the five senses, and how they bring man and beast into contact with their surroundings. It is a book on perceiving, and shows how according as this faculty is exercised it makes each man such as he is. The following extract from the book shows Mr. Aitken's style, and may perhaps induce some to go to the book itself for more from the same source. He is speaking of the moral sense. "And it is almost a truism to say that, if a man has any taste, it will show itself in his dress and in his dwelling. No doubt, through indolence and slovenly habits, a man may allow his surroundings to fall far below what he is capable of approving; but every one who does so pays the penalty in the gradual deterioration of his perceptions. "How many times more true is all this in the case of the moral sense? When the heart is still young and tender, how spontaneously and sweetly and urgently does every vision of goodness and nobleness in the conduct of another awaken the impulse to go and do likewise! And if that impulse is not obeyed, how certainly does the first approving perception of the beauty of goodness become duller, until at last we may even come to hate it where we find it, for its discordance with the 'motions of sins in our members'!