We are now in condition to see that a sub-branch of science has been omitted. It is a department perfectly well recognized. It belongs by virtue of its purpose to the branch of theoretical science; and yet it varies that purpose. It is the subject of Humboldt’s Cosmos, called by Comte philosophie positive, by Herbert Spencer, synthetic philosophy. Its object is to sum up the results of all the theoretical sciences and to study them as forming one system. I am somewhat inclined to call it popular science; but Spencer’s adjective synthetic is better. It may be still more explicit to distinguish it as reviewing science from the first sub-branch of advancing science.