474 SCIENTIFIC THOUGHT. 



chieal with physical phenomena. Fechner, the founder 



of psycho-physics as an independent doctrine, refers 



notably to two l such instances. They were contributed 



g. by two great mathematicians. Daniel Bernoulli and 



Bernoulli 



andEuier. Leonhard Euler. The former pointed out that the value 

 which we attach morally to the addition to any material 

 possession is not measured by the actual magnitude of 

 such addition, but by the relation it bears to that which 

 we already possess. The first sovereign earned by a 

 poor and starving labourer has an almost infinite value 

 compared with what it has for a person already possessed 

 of a million. Laplace and Poisson referred to this state- 

 ment of Bernoulli, and introduced the terms " fortune 

 physique," " fortune morale," showing that they stand 

 in a simple mathematical relation. The same relation 

 was shown by Euler to exist between our estimate 

 of musical intervals in the harmonic scale and the 

 difference of the number of vibrations of the strings 

 which produce the two notes. It was above a cen- 

 tury before Fechner correlated these isolated remarks 

 with observations of modern psycho - physics in his 

 celebrated law, of which more anon. 



On the whole, little progress was made during the 

 eighteenth century in the department of research I am 

 now dealing with; but the end of the eighteenth and 

 the beginning of the following century brought several 

 important discoveries, some of which were at the time 

 much over-estimated, whilst others were for a long time 

 forgotten or overlooked. 



The first is the accidental discovery by Galvani in 



1 'Psychophysik,' 1860, vol. ii. p. 548, &c. 



