Conclusions.–1. Experimental psychology differs from the older introspective psychology only in the accuracy and trustworthiness of its results.
2. All measurements involve both physical and psychological elements; in physical measurements the psychological elements are kept at a minimum and vice versa.
3. Measurements may be of all degrees of accuracy, but in each case the degree of accuracy must be known and stated.
4. The lower grade of accuracy in psychological measurements is due to the inability to maintain more constant conditions. This furnishes no excuse for still further lowering the accuracy by careless methods.
5. The inference seems justifiable that the main work in psychology should be directed to the attainment of constant conditions and the simplification of methods.
