The Measurement of Small Capacities 91 



ring condenser could be made exactly the same in length and position, 

 no further correction would be needed. This condition could, however, 

 never be secured completely, and the correction applied is perhaps a 

 little too large in the case of two or more insulators in series. The 

 error from this source is small, however, since the lead correction is 

 never much more than 20 per cent, of the whole capacity, and Method 

 I. gives exactly the same lead capacity for two or three insulators in 

 series as it does for one. 



In concluding, the writer wishes to thank Dr. A. S. Eve for his kindly 

 interest in the work and Dr. L. V. King for many valuable suggestions. 

 McGill University, July, 1920. 



Summary 



The Measurement of Small Capacities of the order of 10 micro- 

 microfarads is studied with special reference to that of High-Tension 

 Porcelain Suspension Type Insulators. 



Two variations of an Alternating-Current Bridge method are given, 

 namely, 



I. Comparison with a Muirhead Air Condenser, 



II. Comparison with a Guard-Ring Condenser. In this case, the 

 conditions necessary for the use of a Guard-Ring Condenser are obtained 

 by means of Double Balance. 



Two tables are given of the values of the capacities of various types 

 of these insulators singly and in series. 



