532 Prof. H. F. Weber's Researches on 



s oi s i) s 2 , • • • observed at the moments t , J l3 t 2l . . . separated by 

 the same time-interval At, must therefore be constant if FicVs 

 elementary law is the expression of the reality. 



Results of the Observations. — In order, first of all, to show 

 to what nicety the observations can be carried by the second 

 method, I will state in detail the whole of the observations 

 which I have obtained in the first series made according to 

 this method. 



The space between the two zinc plates of the diffusion-vessel 

 (L = 0*522 centim.) was filled, on the 30th October, at ten 

 o'clock, with a solution of zinc sulphate of the concentration 

 0'3120. After the filling, not the slightest trace of electro- 

 motive force appeared between the two zinc electrodes. There- 

 upon a galvanic current, maintained accurately constant, of 

 the intensity 1*1 (mgr.'mm. 1 sec. -1 ) in electromagnetic mea- 

 sure, was passed, from ten till twelve o'clock, in the direction 

 from below upward, through the diffusion-vessels. From 

 twelve to half-past one the diffusion-vessel was left untouched, 

 at a constant temperature ; the observations of the further 

 course of the electromotive force between the two zinc elec- 

 trodes commenced at about half-past one. Every two minutes 

 the diffusion- vessel was inserted for the duration of a half- 

 vibration of the needle (5'2 seconds) in the circuit of a sen- 

 sitive galvanometer with a considerable damping; and the 

 first deflection observed. The needle came to perfect rest in 

 about 1tt minute ; so that this was the initial state of the needle 

 at each observation. The resistance of the diffusion-vessel 

 was vanishingly small compared with the resistance (366 

 m. u.) of the rest of the galvanometer-circuit. 



The following Table gives, in the second and fifth columns, 

 the first deflections s obtained (reduced to arcs) ; in the third 

 and sixth columns stands the temperature of the diffusion- 

 vessel, noted every ten minutes. The last column gives the 

 differences of the ordinary logarithms of each two deflections 

 which are distant half an hour from one another. The num- 

 bers of this last column show with sufficient distinctness the 

 accuracy of observation that can be attained in this way, and 

 to what degree the elementary law which forms the foundation 

 of the theory corresponds to the facts. They, further, make 

 it evident that the determination of the quantity of diffusion, 

 k, can with tolerable exactness be effected from a few obser- 

 vations made during a fraction of an hour. 



