( 444 ) 



envelophif/ curve will represent Ihe manner in which a jndgment 

 about the linal i-esiiU originates. To obtaiji tlie envelope of the 



group of ctii-ves <> -^ A' — — - , if the conshuil /// is changed, we put : 



run 



OF 

 ('alciilaling Ihc \aliio of /n coiTospoiKliiig jo = 0, and subsli- 



tuling Ihis \aliie iiilo liie e<piali()n /' = 0, we liiid tlic forninhi for 



the ein<'l(>|ting ciiixe. We may slate: 



OF K „,. mBJl—l 



— =r . 8"'/?/i. — (7) 



07)1 R Vl^ 



1 



From whieh follows m =-= — — , whieh substituted ink) /'= 0, gives : 



liJi 



Q — Klh (8) 



proving (hat the rchilirc iiijj't'i'i'iil'nil fl/rcs/ui/drif/iic is coi/s/jn/f. 



By this i)roeess we ha\ e deduced from our formula the law of 

 Weber. 



From onr dednetion may be interred that the area, wherein the 

 law of Weber prevails, is a liuiited i)ne. Tlie Aalidity of Ihis law 

 commences within the area of the enveloping cuixe, and a look on 

 the iigure "2, will uiakc it clear thai the lii-st part of the whole 

 sensation-cnrve is gixen by the descending part of the cur\e 



o := K . The hoi-izontal |>art tlicn represents the ai'ca \\ilhin 



R ' 



the limits of which the law of Webek pi'e\ails, \\liilst in the case of 



verv great intensities of stimuli the ascending part of the curve 



O = /v Avill appear. 



There remains still another conclusion to be drawn from our 

 deduction. This latter was founded on the sup|)osition that the increment- 

 constant /> was the same for all stimulated neui-ones. This, however, 

 is highlv improbal)le: in the most tavoui-able cases we may oidy 

 suppose that the /->-coetïicient of the homogenous neurones will 

 possess ai)pi"oximatively the same value, IVom which follows that 

 we may admit the law of Weher at l)est as an approximation. 



Finally it may be mentioned here that apart from tlie above- 

 demonstrated correction for obtaining an approximation in the dii-ec- 

 tion of the law of Weber-Feciinek, i)robably still anothei- means of 

 correction exists in some of our sense-organs; 1 shall proxe this in a 

 later communication. 



