1890.] 



Analogue of the Wheatstone Bridge. 



467 



I. To Verify the Law of Proportionality of Areas, viz., ^1 — ^3. 



As already stated, a s = 0*5 sq. in., a 4 = 1 sq. in., so that if the law 

 holds a 3 should be found to be equal to 2a v In testing the propor- 

 tionality, a 1 was made successively equal to \, J, j, 1 sq. in., by the 

 use of a cardboard wedge, 343 mm. length of which corresponds to 

 1 in. breadth ; and a 3 was adjusted till there was no flow through the 

 galvanometer tube, and the width measured by means of the card- 

 board wedge. 



The measurements were referred directly to an inch scale by 

 parallel -jaw callipers. 



The observations are contained in the following table : — 



Table I. 



Area of a x in square inches 



•25. 



•50. 



•75. 



1-00. 





r 



165 



337 -5 (?) 



495 -5 





"68 -5" 





Observation of width of 





165 



333-5 



496 





"68 -5 = 





a 3 in divisions of the< 





166 



333-5 



495 





"69 -0" 





wedge 





166 



333-5 



494-5 





"68 







165 



334 



494-5 





= 67 -0] 







165-4 



334-4 



495-1 



[68-2] 



Equivalents in square inches 



•465 



•985 



1-46 





1-92 





a z 





1-86 



1-97 



1-95 





1-92 





a x 

















The differences in the ratios a z \a\ for different values of a 1 are con- 

 siderable, but it must be remembered that the greatest fractional differ- 

 ence, being l/19th of the whole, would be accounted for by an error of 

 l/76th of an inch in the adjustment of a 1 to J inch, and a cardboard 

 slit, cut with a knife, can hardly be expected to reach beyond that 

 limit of accuracy. It is evident, from the readings given, that the 

 condition of no flow is capable of very accurate experimental definition 

 with the little compass detector. 



II. Verification of the Inference that the Condition of No Flow is 

 Independent of the Total Head. 



This has only been carried so far as to determine whether, when 

 the adjustment of areas was made, the equilibrium could be dis- 



* The readings in this column were taken by means of a different and wider 

 wedge. 



