Capacity of Solids under varying Fields. 



89 



to obtaining the final result many different dispositions of the 

 apparatus were tried, and the method tested in most of its 

 features. Experiments were also made upon a block of 

 paraffin smaller than the large plate ; but it was found that 

 the results were incorrect in this case, which fact makes it 

 necessary to use blocks of the same size as or larger thau the 

 plates of the apparatus. 



In obtaining the final values, the apparatus was adjusted 

 so that d 2 -\- d 4 — 3'51 centim., and D was changed until the 

 capacities of the two sides were nearly equal. In all cases 

 superior and inferior readings were taken as previously 

 described, and the mean taken as the true reading. The 

 following characteristic set of ten readings, taken with slow 

 fields, are given to illustrate the accuracy with which the 



plate may be adjusted. One scale- division 

 d± = 2 scale-divisions. 



centim. 



1 



13-82 



2 



14-32 



3 



13-80 



4 



14-20 



5 



13-78 



6 



14-22 



7 



13-80 



8 



14-22 



9 



13-79 



10 



14-20 



14*015 = mean. 

 8*450 = zero-reading of scale. 



5*565 = d 2 . 



The final values obtained for paraffin are embodied in the 

 following table. The value for slow fields differs a trifle from 

 that published in a preliminary article ; further experience 

 with the apparatus having led to the present value. 



Slow Fields. 



? 4 in scale- 



Number of 





divisions, 



Readings. 



K. 







20 



2-316 



1 



20 



2-334 



2 



20 



2-322 



3 



20 



2-303 



Total . . 80 Mean 

 Called K = 2-32. 



2*319 



