Apeil 4, 1913] 



SCIENCE 



533 



Lalanne' and Mach,° giving the fusion limit 

 far below the range I employed, throw doubt 

 on the other results, and make it evident that 

 there is somewhere in the determination a 

 factor which has escaped attention by one 

 group or the other of the experiments, or pos- 

 sibly by both. 



The early observations were made with little 

 reckoning of the troublesome psychological 

 problems involved, and with no reference to 

 the possibility which we must at present ad- 

 mit — that vibratory stimuli applied to certain 

 portions of the skin may rouse sensations 

 other than those of pressure, touch, tempera- 

 ture or pain: sensations of vibration, or palm- 

 esthetic" sensations, as they are provisionally 

 designated. The former point we will con- 

 sider below; the latter is of prime consequence. 



K an observer assumes that when a tuning 

 fork (the stem of it or some attachment to a 

 prong) is applied to the skin the sensation 

 aroused will be either that of mere continu- 

 ous touch or pressure (we may leave out of 

 account pain and temperature, as being easily 

 discriminated from the other), as when the 

 fork at rest (not vibrating, that is) is ap- 

 plied; or else of the discrete series of touches 

 corresponding to the individual periods of the 

 vibration, his observational problem will be 

 comparatively simple. If the fork is per- 

 ceived as being in vibration, the judgment 

 will be " discrete pulses," or " series of dis- 

 crete tactual sensation " ; if the fork feels as 

 if not vibrating, the judgment will be 

 "fusion." In other words, the problem of 

 observation is restricted to the question 

 whether or not the fork can be perceived to 

 be in vibration. This, we may reasonably 

 infer, was actually the problem as understood 

 by a number of the experimenters, and conse- 

 quently the thresholds of fusion they reported 

 were limited simply by the mechanical ca- 

 pacity of the forks (or whatever serial stimu- 



' Lalanne, ' ' Sur la durge de la sensation tac- 

 tile," C. B. de I'acad. des sci., LXXXII., 1314. 



' Maeh, E., Siteber. d. Weiner Akad., LI., 2, 142. 



" The term was introduced in German, by Eydel 

 and Seiflfer in 1903. 



lation devices were employed) to produce a 

 sufficiently intense vibratory stimulus. 



When we admit the possibility that the 

 vibration of the fork may produce a sensation 

 which is not identical with the simple touch 

 or pressure sensation, the problem becomes 

 entirely different. It is now a question of 

 determining the point (in rapidity of stim- 

 ulus) at which the sensation enters, or the 

 point at which it becomes a continuous sensa- 

 tion; or possibly we may have to make both 

 determinations. That there are abundant 

 clinical observations which go to show the 

 existence of a palmesthetic sensibility not 

 identical with touch or pressure, I pointed out 

 in my first paper. 



The forks with which I first worked (in the 

 neighborhood of 440 vibrations per second) 

 were too heavy for their length, and the vibra- 

 tion-feeling consequently feeble and of brief 

 duration. I have since secured some forks 

 which are better adapted to the work, being 

 relatively more slender, and have carried on 

 observations with these. They have prongs 

 approximately 8 X 5-5 mm. in cross section, 

 and 19 cm. long for c (128 per sec.) and 13 

 cm. long for c' (256 per sec). The c^ forks 

 of the same cross section, 9 cm. long, are less 

 satisfactory. The forks have been fitted (by 

 our mechanic) with tubular brass extensions 

 to the stems, giving a total length from the 

 crotch of 9.5 cm. The end of the extension 

 is solid, with a diameter of 1 cm. Weights 

 with clamp-screws are fitted to slide on the 

 prongs so that the forks may be tuned from 

 the original c and c' down to the F and f 

 below, by any required steps. 



These forks were prepared primarily for the 

 purpose of determining difference-sensibility 

 in the octaves represented. This work has 

 not been completed, but shows, so far, about 

 the same threshold as was earlier obtained in 

 the middle octave (approximately 10 per 

 cent.). The present report is not concerned 

 with this measure. 



We early noticed that beats were palmes- 

 thetically perceived, and were as distinct and 

 characteristic as auditory beats. With prop- 

 erly tuned forks, we found differential sensa- 



