552 MEASUREMENT OF RESISTANCES IN ABSOLUTE VALUE. 



The three other methods seem open to no objections, in the 

 present state of our knowledge. 



If we eliminate from the third series the number of F. Weber 

 (which is manifestly too small), the two first numbers of the sixth 

 series, and the first of the seventh, they give respectively as means : 



3rd Series ... ... ... 106*25 '5 



6th ... ... ... 106*20 0*05 



;th 106-15 0-10 



Mean 106*207 0-069 



It will be thought, perhaps, from these means, and from the 

 examination of isolated experiments, that the true value of the ohm 

 is between 106*2 and 106-3. We know, further, that the Inter- 

 national Commission, not being fixed as to the value of the fourth 

 cipher, has adopted as legal ohm the round number 106 centimetres. 



The standard of the British Association, referred to the legal 

 ohm, would then be 



104*8* i 



0-98895 



106 1-0112 



A circumstance, which has not been sufficiently taken into 

 account in the experiments, and to which Lord Rayleigh has 

 called attention, is the want of insulation of the windings of the 

 coils. This cause of error may be very important in experiments 

 in which, the electromotive force of induction being variable, may 

 at a given moment attain a high value ; it is possible that the 

 insulation in that case leaves much to be desired, while it would 

 be sufficient for weak and continuous currents. 



In the simplest case, in which two or more windings of the 

 induced circuit are in contact, the inaccuracy of the result would 

 obviously represent an error of one or more units in the number 

 of windings ; its effect is to increase the numerical value of the 

 resistance observed, and to diminish that of unity. An effect of 

 the same kind is produced when the want of insulation is variable 

 with the electromotive force ; so that, from this point of view, the 

 higher numbers are the more probable. 



