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Visual illusions : the illusion of compared horizontal and vertical lines ; the Muller-Lyer illusion. Tactile discrimination ; Aristotle's illusion and its modiJcations. Sensibility to pain. O@ctory acuity. Taste names. Hearing. Conclusions. of the Gunning Fund of the Royal Society f o r the years 1901-2.1 l'he purt played by irgerence in the determinution of a threshold. No dejinite racial diferences in the acuity of the senses. Injluence of age o n acuity. &elation between colour-nomenclature and colour-sense. Frequency of colour-blindness in tJLe Todas. Some illusions experienced more stronyly by the savage than by the civilised subject, and others less strongly. Variability in psychological tests und the factors by which the measures of variubility are injluenced. Correlatiort between the simple mental operations tested and general intellectual development. ' 8W Reports, pp. 20-23. * By this it is not meant that the recognition of distant objects in ordinary life is not This is a much more complex process than that involved in influenced by illumination. the experimental determination of visual acuity.

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THE research of which an account is to be given in this article differs in several respects from previouis attempts to determine the influence of caffeine on the capacity for muscular work in man. The method which has been usually employed has been to take a continuous series of ergograms at intervals of two to five minutes and to administer the caffeine either before or at some stage in this continuous series. Such a method gives no adequate means for the determination of any differential action of the drug in the fresh condition and after fatigue has been produced by the performance of a certain amount of work. We have therefore tested the effect of the drug on the work recorded in sets of ergograms separated by intervals of rest so that we have been able to examine not only the influence of the drug at different intervals after its administration, but also its action at the beginning of, and throughout each set of ergograms.In another important respect our work differs from all that previously recorded, in that on the normal or control days we have taken doses of a mixture which we were absolutely unable to distinguish from that containing the caffeine'. In this way we have not only eliminated any possible influence of suggestion, but also the much more important sources of error arising from the sensory stimulation produced by swallowing the drug and from the interest due to the act of taking it.Each experiment was prolonged over a number of days, on some of which a dose of caffeine was taken, and on others a dose of the control. Both the caffeine and control mixtures were in most cases prepared for us by Dr W. E. Dixon for whose kind help in this respect we are very greatly indebted.