Intelligence and Miscellaneous Articles. 383 



variations of the horizontal component in a building where much 

 iron has been used in the construction. 



The following are the details of an experiment ; they enable us 

 to judge of the value of the method, and the agreement of the 

 observations. This experiment was made on the 13th April 1886, 

 at La Solitude in the suburbs of Lille, in the centre of an open 

 space of several acres, and at a distance from any buildings and 

 from water- or gas-pipes. 



Deflections of the Galvanometer. 



Right. Left. 



Time. ^ * ^ , * ^ 



h m 



4 



4 5 33-75 34-15 



4 25 .... 33-25 33-50 



4 35 . . 33-85 33-50 



4 55 . . 33-40 33-00 



General Mean 33°-55=33°-33. 



Observations of the Voltameter. 



mgr. 



Loss of the Soluble Electrode 360 



Gain of the Negative Electrode 355 



Mean 357'5 



1 357-5 



10 1190 ==0 ' 233 T tan 33 ' 33 - 

 T = 0-187. 

 This value of T will serve as a point of comparison ; it is less 

 than the value observed at Paris on the 1st January 1886, as was 

 to be expected from the position of Lille. We consider it exact to 

 within 3 or 4 thousandths ; in fact an observation made after the 

 first gave 0-185, and a great many experiments made in the 

 laboratory showed that the result of an experiment never differs 

 by more than ytfVfF ^ rom tne mean of a month of investigations. 



The table given below gives the value of T obtained in various 

 parts of our establishment. 



Place. Date. T. 



La Solitude near Lille April 13 0-186 



Lesquin near Lille „ 4 0-191 



Outer court of the Faculty „ 1 0-183 



Inner court of the Faculty May 21 0-190 



Professor's Eoom „ 31 0-152 



Physical Cabinet Mar. 23 0-134 



Hall A „ 29 0-133 



HallB , „ 30 0-114 



Vaulted Hall July 21 0-194 



It follows from these researches that T may be reduced by 40 or 

 50 per cent, in a building made of iron ; hence the same current 

 will give in the same galvanometer a deflection of 33° to 45° 



