1896. NOTES AND COMMENTS. 219 



above and beyond those which reign in the inorganic world — the 

 definition and measurement of such forces, so as to bring them within 

 the range of experiment — these are tasks which may await the physi- 

 ologists of the future. Professor Sanderson does not, it is true, take 

 too hopeful a view as to the likelihood of such discoveries. Yet 

 following on the lines along which physiology has already progressed 

 so far, when all that is explicable by known physical and chemical 

 law has been explained, the as yet unknown and undefined " vital 

 forces," if such exist, will stand out the more clearly, and present a 

 more definite front for attack from the experimental side. 



Experimental Psychology. 



A YET newer form of science is experimental psychology. The 

 wonderful energy with which the American Universities have taken it 

 up bears fruit in many interesting records of laboratory work, published 

 in the American Journal of PsycJiology, or the Psychological Review, or 

 independently. The Yale Psychological Laboratory, which is under 

 the direction of Dr. E, W. Scripture, has pubUshed the record of its 

 third year of work. If the output seems small, it must be remembered 

 how much time has to be spent in organising a new laboratory and in 

 providing apparatus. Among the new apparatus described is a very 

 simple instrument for testing colour-bHndness and also for detecting 

 colour-weakness. It depends on the use of different intensities of 

 light : a simple arrangement resembling that of an ophthalmoscope 

 allows red, green, and grey to be seen together in different shades, the 

 colours being looked at through three windows fitted with grey 

 glasses of different darkness. There are two principal researches in 

 the volume. The first, by Dr. Seashore, is an interesting study of 

 " illusions and hallucinations in normal life." He traces the influence 

 of the size of objects on our judgment of weight, larger objects of the 

 same weight being over-estimated, and smaller ones under-estimated. 

 Noteworthy is the persistence of the illusion in spite of practice. In 

 a second set of experiments Dr. Seashore found that it was possible 

 by exciting expectation to produce hallucinations of various kinds in 

 the absence of any physical stimulation. Sometimes there was a 

 direct suggestion, sometimes the repetition of the stimulus a sufficien 

 number of times led the patient to imagine it when it was absent. 

 Thus hallucinations were produced of warmth, of a least perceptible 

 difference of two lights, of a change in the intensity of illumination, 

 even of actual objects. This investigation, though not surprising, is 

 of some importance in itself, and as indicating a source of error 

 in psychophysical experiments. Dr. Moore has a study of how 

 fatigue affects the accommodation of an eye that is endeavouring 

 to locate a point half way between two others on the line of sight. 

 The error grows immensely with fatigue, though less with the single 

 eye than with the two eyes. Some experiments are also recorded by 



R 2 



