James Thomson is known primarily by his masterpiece, The City of Dreadful Night, Because of the overwhelming pessimism of this work, Thomson may seem to have been a weak character who was unable to stand up to the disappointments and pressures of life. This, I believe, is an inadequate conception of the man. For a better understanding of Thomson both as man and poet, I believe a study of his earlier, relatively unknown poem entitled The Doom of a City is necessary. This early poem shows Thomson as a healthy young man with the normal desires to believe in a principle of good and in an all-wise God who is in control and will triumph in the end. It shows him as a humanitarian and reformer who feels people can be helped to an improvement of their lives. It shows Thomson at a time before his rationalistic mind caused him to reject the ideas of an omniscient and loving God, of immortality, and even of the possibility of reform and progress. It indicates that these rejections were not achieved without a struggle. By the time Thomson wrote The City of Dreadful Night, the rejection had taken place, and Thomson could no longer believe in the vision of the living God which he had seen in The Doom. Science for him had stripped away all such pleasant illusions. Thomson’s pessimism seems to be not so much the result of his frustrations and inability to stand up to the problems of life as the result of his complete acceptance of the scientific thought of his age coupled with his intellectual honesty in facing up to life and refusing to accept anything without rational proof. In my study of Thomson, I discuss first the scientific and religious thought of the nineteenth century as it relates specifically to Thomson; second, Thomson’s early attempt in The Doom of a City to develop a meaningful creed which his mind could accept; third, the ideas in The Doom of a City which are repeated throughout Thomson’s career; fourth, the changes in Thomson’s creed as revealed in The City of Dreadful Might; and finally, the tendency toward a contradiction between the agnosticism of his essays and the atheism of his later poems, particularly She City of Dreadful Might.