according to the Observations at Munich and Brussels. 251 



The result of these observations is, that the electric tensions 

 in winter and summer are to each other, for Brussels as 9 to 1, 

 for Kew as 6 to 1, and only as 2 to 1 for Munich. Diiferences 

 of such magnitude, if they really exist, possess the highest scien- 

 tific interest ; if they are due to the imperfection of the instru- 

 ments, they merit scarcely less attention. 



It is essential, in the first place, to examine if the cause of 

 these chfFerences resides in the manner in which the observations 

 have been collected, or m their mode of calculation. 



Although applying the instrument of Peltier, with some mo- 

 difications, you have pm-sued a different method from that fol- 

 lowed by the above-named physicist to render your results com- 

 parable. M. Peltier estimated the value of the degrees of his 

 instrument by transferring the electric charges directly to Cou- 

 lomb's balance ; and he indicated by a table the electric tension 

 corresponding to every angle of deviation ^ of the moveable 

 needle of his electrometer. 



I have employed a similar table based upon a principle some- 

 what different, that of dividing the electricity between two balls 

 of equal surface. I have found that the table calculated in this 

 manner for the degrees of my electrometer, agrees perfectly with 

 that calculated by Peltier from his experiments for the same in- 

 strument. The two methods of experiment thus exhibit the 

 same results. 



You have preferred following another way : you have had 

 recourse to calculation ; and, admitting the hypothesis that the 

 electricity is uniformly distributed in the conductor and in the 

 moveable needle, you find that tlie electric tension rj is very nearly 

 proportional to the angle ^; so that we may take 7; = 0"-J-P((^), 

 • Tliesc numbers belong to 1850, the preeeding to 1851. 

 t The notice gives the number 75'4, which is not tlie mean of tlic year. 



