Man builds houses out of bricks and timbers. Is not the house something different in kind from the trees and the clay from which the materials have been taken? Is not the boiler of a steam-engine different in purpose and accordingly also different in kind from a tea-kettle? Is not every invention something different in kind? And is not the same true of the products of thought? Is not a triangle something different in kind from a line? And the origin of the former is not more miraculous than that of the latter. A triangle is more complex than a line, but its existence in the mind is not more of a mystery than the existence of the line. Difference in kind need not include difference of origin. Harmony is different in kind from melody. Notes in succession produce melody, while simultaneous notes produce harmony. In either case it is simply a matter of combination. Professor Romanes when speaking of the passivity of sense-impressions seems to think of the unconsciousness of the process. We are not conscious of the transformation of impressions into sensations while we can become aware of our efforts to change the sense-material into concepts. Yet the nature of mind is throughout activity. And no one has perhaps insisted more strongly on the activity of mind than Prof. Max Müller. But Prof. Max Müller distinguishes between the activity of the mind and the ego which as he supposes performs that activity. He says (“Science of Thought,” p. 63): “We think of a mind dwelling in a body, and we soon find ourselves in the midst of psychological mythology. Let it be clearly understood, therefore, that by Mind I mean nothing but that working which is going on within, embracing sensation, perception, conception, and naming, as well as the various modes of combining and separating the results of these processes for the purpose of new discovery. “But if Mind is to be the name of the work, what is to be the name of the worker? It is not yet the Self, for the Self, in the highest sense, is a spectator only, not a worker; but it is what we may call the Ego, as personating the Self; it is what other philosophers mean by the Monon, of which, as we shall see, there are many. Let us call therefore the worker who does the work of the mind in its various aspects, the Monon or the Ego.” And in another passage (l. c., p. 552) he speaks of the simplicity of the monon: