G8 GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 



time-piece) ; so that this mode of measuring the intensity re- 

 quires less expense than any other magnetic determination. It 

 is also very portable and convenient for travellers. The appa- 

 ratus is to be placed on a table in the middle of a room, avoiding 

 all iron in the neighboui-hood ; large iron rails, even at some 

 distance, must be carefully avoided. Arrangements may also 

 easily be made for emplo^nng it in the open air. 



2. Observations to be made with this apparatus. 

 These are of two kinds: 1. The experiments of deflection. 

 2. The experiments of vibration. 



1. The experiments of deflection. 

 The measuring scale is placed horizontally, and at right angles 

 to the magnetic meridian, with its zero point towards the east, 

 and the needle in the centre. The small magnet bar is to be 

 placed successively as follows : 



1. With its north end to the east, on the zero point of the 

 scale : if the length of the small magnet bar is 100 millimetres, 

 its centre will then be over the division 50"^™ of the scale. The 

 needle will be deflected towards the east, and its position, u^, 

 is observed. 



2. The south end is then substituted for the north end. The 

 needle is deflected to the west, and its position, «(,', obser\'ed. 



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

 east, on the division 100 millimetres. The needle is deflected 

 easterly, and its position, u^, observed. 



4. The bar is again reversed, end for end. The needle is de- 

 flected westerly, and its position, «/, observed. 



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

 east, upon the division 150 miUimetres. The needle is deflected 

 easterly, and its position, u^, obsei-ved. 



6. The bar is again reversed, and the needle deflected westerly, 

 and its position, Ucl, observed. 



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

 east, upon the division 750 milUmetres. The needle is deflected 

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



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

 its position, «.,'", observed. 



9. The nortl end of the magnet is placed towards the east, on 

 the division 800 millimetres. The needle is deflected easterly, 

 and its position, «/', observed. 



