24G 
Proceedings of the Royal Society 
Monday, Zrd Becemher 1883. 
The Eight Hon. LOED MONCEEIFF, President, 
in the Chair. 
The following Communications were read 
1, An Essay upon the Limitations in Time of Conscious Sen- 
sations. By John B. Haycraft, M.B. Edin., F.E.S.E., &c. ; 
Professor of Physiology in the Mason Science CoEege, 
and Lecturer on Physiology at Queen’s College, Birming- 
ham. 
I propose to describe in this essay some experiments which I 
have conducted upon the limits in time of separate tactile and 
thermal sensibilities. I shall endeavour to account for the variations 
seen in the limitations in conscious sensation of the different senses; 
and also to formulate a general proposition as to the effect on con- 
sciousness of stimuli increasing gradually in rapidity of application. 
If the finger he touched with a pin, one is both conscious of the 
point in time at which the contact is made, and also when it is 
broken ; this is likewise true of the other sensations. In the case 
of hearing, for example, a note struck upon the pianoforte is 
localised in time as of a certain duration. In moving an object 
through the field of vision, it is seen definitely to pass into, and also 
out of that field. 
There is, however, a limit to this which can he determined, for if 
the image just alluded to be brought — by means of a revolving 
wheel — fifteen or twenty times a second in front of the same point 
of the visual field, it will now he seen as a stationary object, and the 
separate stimuli will produce a continuous sensation. In the case 
of hearing, Helmholtz has shown {The Sensation of Tone as a 
Physiological Basis for the Theory of Music, p. 262) that the limits 
in time are sharper and more exact. The ear can, according to this 
observer, distinguish 132 heats (produced hy high notes) in a 
second ; even this being probably not the extreme limit. It is also 
!;,nown that over 1400 impacts from a revolving toothed wheel must 
