This essay of 102 pages characterises most excellently some of the proceedings and methods of Professor Wundt’s psychological laboratory. The author, a disciple of Wundt, is a native American who studied in Berlin, Zürich, and Leipzig, and took his degree of Doctor on the ground of this dissertation. The object of the treatise is not so much to solve as to formulate the problem of the associative course of concepts, and the author hopes that in a future treatise he will be able to propound his theory based upon the facts here related. The experiments were made with the assistance of seven friends, among them German students, a doctor of philosophy, a doctor of medicine, and a teacher. They were of different nationality, three Germans, one Belgian, one Japanese, one Englishman from the Cape, and two Americans, the author included. The apparatus used was so arranged that the person operated upon sat in the dark, before him was a plate of ground glass intercepting from a camera an image which was exposed for four seconds. Pictures of all kinds, colors, and plainly printed words were used. For other sense-impressions the observer was also seated in the dark. Several instruments for producing sounds were ready on a table. Tastes were effected by liquids which the person operated upon had to drink, and the sense of touch was investigated through handing him cards to which some small objects had been attached. The author was partly operator, partly observer, i. e. the person operated upon. The ideas evoked through the sense-impressions produced in this way, are enumerated in tabular form in the order in which they arose. Among the experiments made in this way we find one kind which is of special interest. Sir William Hamilton made the remark in his Lectures on Metaphysics that unconscious ideas may serve as connecting links between two ideas otherwise unassociated. He represented his view in the following way: Let _A_, _B_, _C_, be three ideas, _A_ does not suggest _C_, but both are associated with _B_. It happens that _A_ is directly followed by _C_ in consciousness. In such a case _A_ may recall _B_ and _B_ may recall _C_, but _B_ being a _minimum visibile_ or _minimum audibile_ does not enter consciousness. Thus the idea of the mount Ben Lomond called into Hamilton’s mind the system of Prussian education. Subsequent reflection taught him that he had met on Ben Lomond a German. The recollection of the place was associated with the ideas—a German, Germany, Prussia. These ideas were too weak to enter consciousness yet they reawakened another idea which did enter consciousness, the system of Prussian education.