GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 69 



10. The bar is reversed. The needle is deflected westerly, 

 and its position, m,'", observed. 



11. The north end of the magnet bar is placed towards the 

 east, on the division 900 milhmetres. The needle is deflected 

 easterly, and its position, u^', observed. 



12. The bar is reversed. The needle is deflected westerly, and 

 its position, uj'', observed. 



These twelve observations may all be completed in half an 

 hour. 



2. Experiments of vibration. 



The small magnet bar is to be suspended horizontally by a 

 silk thread, to be set in vibration, and its time of vibration 

 observed in the usual manner, which needs no further description 

 here. The time of vibration may be deteraiined by these expe- 

 riments, with sufficient precision, in a quarter of an hour. 



Taking together all the observations which are necessary for 

 a complete measure of the absolute intensity, and aUoAAing a 

 quarter of an hour for an'anging the apparatus and suspending 

 the magnet bar, the experimental part of the determination can 

 be completed in one hour. The observer may give his determi- 

 nation greater certainty and accuracy by repetition. 



The following observations made with this instrument at Got- 

 tingen are given as an example. 



Gottingen, January 18, 1837. 

 1. Experiments of deflection. 



1. Uq - ud = 23° 9' 



2. Wi - w/ = 47° 42' 



3. % - < = 71° 48' 



4. uj' — nj" = 69° 21' 

 3. M," - ^«/" = 46° 12' 

 6. <' - Mo'" = 22° 27' 



In these experiments, the distance, R, of the centre of the small 

 magnet bar from the centre of the compass, was successively, 



1. i?o = 450B»«» 



2. l?i = 350 



3. R^ = 300 



4. i?2 = 300 



5. Ry = 350 



6. Rq = 450 



