Moment of Inertia of Maqnets. 



133 



Amplitude 



/at commencement 4° 

 [at end 1° 30 



Temper 



r 14° -9 

 ature j ^.^ 



14°-9 



14° -7 



Times of Transit. 

 Scale moving to right. 



Difference. 



1 



Times of Transit. 

 Scale moving to left. 



Difference. 



h m s 

 11 46 13-6 



47 137 



48 13-8 



49 14-0 



50 14-0 



h m s 

 12 6 151 



7 152 



8 15-3 



9 15-4 

 10 15-6 



m s 

 20 1-5 j 



1-5 



1-5 



1-4 1 



1-6 j 



h m s 

 11 46 34-2 



47 34-4 



48 34-5 



49 34-6 



50 34-6 



h m s 

 12 6 35-7 



7 36-0 



8 36-0 



9 36-0 

 10 361 



m s 

 20 1-5 

 1-6 



1-5 

 1-4 

 1-5 



4 04 



16 1-6 



12 6 15-6 



Mean ... 



20 1-50 



4 0-4 



16 1-6 



12 6 362 



Mean . . . 



20 1-50 



Approximate period determined with stop-watch =3*75. 

 Hence in 60 sees, there are 16 vibrations, and in 4 m. 04 s. 

 there are 64. Thus in 16 m. 1*6 s. there are 256. Hence 

 the number of vibrations corresponding to each o£ the above 

 differences is 320. 



Mean time for 320 vibrations 

 „ ,, one vibration , 



20 m. 1-50 s. 

 3*7547 sec. . 



The period of the cradle alone has also to be determined, 

 and it will be found convenient to adjust the period by the 

 weights D to nearly one second, so that the method of co- 

 incidence may be conveniently employed. 



The following table gives particulars of the different inertia- 

 bars which have been compared. 



Distinguishing 

 number. 

 1. ... 

 9. 



Material, &c. 

 Rolled brass. 

 Cast silver. 



3 Rolled copper. 



4 Copper with 0*5 per cent. zinc. Cast. 



5 Copper with 0-5 per cent, phosphide of tin. Cast. 



6 Gun-metal. Cast. 



7 Rolled copper. 



8 Rolled copper. 



9 Rolled copper. 



10 A rolled brass bar with slightly rounded corners 



and gilt. 



Note. — Bars 2, 4, and 5 were made from castings prepared with very 

 great care at the Royal Mint under the direction of Dr. Rose ; and I am 

 much indebted to him for the trouble he has taken in the matter. 



The bars were turned and then ground true, while special 

 care was taken to have the ends plane and perpendicular to 

 the axis of the cylinder. In the case of bars numbers 7, 8, 

 and 9 the ends were ground and polished to an optical surface, 



