350 



EEPORT — 1864. 



Appendix A. — Description of a further Experimental measurement of Electrical 

 Besisfance made at King's College. By Prof. T. C. Maxwell and Mr, 

 Pleeming Jbnkin, with the assistance of Mr. Charles Hockin. 



The method employed in these experiments has been fully described in Ap- 

 pendix D. to the Report of 1863. In the new experiments, the elements of 

 the calculation were varied as much as possible ; fresh wire was wound on 

 the experimental coils ; observations were made with velocities differing 

 widely from one another. Fresh measurements were made of all the cor- 

 rections required, and greater precautions were taken to avoid local disturb- 

 ances. 



n, the number of windings, was .... 319. 



I, the effective length of the wire .... 311-2356 metres, 

 the mean circumference 0*993987 „ 



a, the mean radius 0"158194: 



h, the breadth of each coil 0*1841 



26, the distance from centre to centre 



of each coil 0-03851 



c, the depth of the layers 0-01608 



The weight of the wire and silk .... 110 oz. 8 dwt. 



sin^ a = l. 



D the distance from the mirror to the scale ; 2212 miUims. in some 

 experiments, 2116 millims. in others. 

 The following Table gives the result of the experiments, and the com- 

 parison witlr those of 1863. 



Time of 100 



revolutions, in 

 seconds. 



Values found for 

 coil in terms of 

 Kf for each expe- 

 riment. 



Value of B. A. unit in 



terms of 10^ 



metre 



seconds ' 

 as calculated from 

 each experiment. 



Value from 

 mean of each 

 pair of expe- 

 riments. 



Percentage 

 error from 

 mean value. 



17-54 



17-58 



77-62 



70-17 



5.3-97 



54-53 



41-76 



41-79 



54-07 



53-78 



17-697 



17-783 



17-81 



17-78 



17-01 



16-89 



21-35 



21 -.38 



21 -.362 



21-643 



11-247 



16-737 



4-7201 

 4-.5914 

 4-8848 

 4-4871 

 4-6607 

 4-6(i66 

 4-6279 

 4-6275 

 4-6496 

 4-6146 

 4-6108 

 4-7313 

 4-6452 

 4-7489 

 4-7567 

 4-6187 

 4-6834 

 4-6727 

 4-6526 

 4-7134 

 4-8658 

 4-5.305 



1-0121 

 0-98.36 

 10468 

 0-9613 

 0-9985 

 0-9998 

 0-9915 

 0-99-36 

 0-9961 

 0-9886 

 0-9878 

 1-0136 

 099.52 

 1-0174 

 1-0191 

 1-9895 

 1-00.34 

 1-0011 

 0-9968 

 1-0096 

 1-0424 

 0-9707 



0-9978 

 1-0040 

 0-9992 

 0-9925 

 0-9924 

 1-0007 

 1-0063 

 1-0043 

 1-0022 

 1-0040 

 0-9981 



-0-22 

 -1-0-40 

 -0-08 

 -0-75 

 -0-76 

 -fO-07 

 -fO-63 

 4-0-43 

 -1-0-22 

 -HO-40 

 -0-19 



Probable error of E (1864) = 0-1 per cent. 

 Probable error of E, (1863) =0-24 per cent. 

 Difference in two values 1864 and 1863=0-16 per cent. 

 Probable error of two experiments=0'08 per cent. 



