THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. IX. — Experiments on High Electrical Resistance, Part 

 II ; by Ogden JN". Rood, Professor of Physics in Columbia 

 University. 



New method of measuring high electrical resistance. — In 

 the first part of this paper,* I have given a general account of 

 a mode of measuring electrical resistances which are far too 

 large to be dealt with by ordinary methods. Since then the 

 electrometer, there indicated, has been improved, and a large 

 number of units of resistance has been constructed. Experi- 

 ments have also been made with regard to the best modes of 

 using them, and, in particular, with respect to the best way of 

 building up a set of high resistances, from a low, but known, 

 resistance. Attention has been paid to electrical leakage, to 

 the composition of the units, to their reliability during short 

 and long intervals of time. Their behavior under different 

 electromotive forces has been somewhat attended to, and is 

 still under examination. A large number of details have pre- 

 sented themselves, and it will require considerable time before 

 they all can be satisfactorily studied. Meanwhile this much 

 has been ascertained : it is possible to take a low standard of 

 resistance, measured by old methods, employing fifty or a hun- 

 dred volts, and from this to build up a set of resistances, the 

 highest of which shall be equal to "fifteen or twenty millions 

 of megohms, the original electromotive force being always 

 adhered to. With such units of resistance it is of course easy 

 to measure any resistance which lies within their range, employ- 

 ing always one and the same electromotive force. The relia- 

 bility of such measurements can be judged from the results 

 given at the end of this article. It is also certain that the 



* This Journal, x, 285, 1900. 

 Am. Jour Sci.— Fourth Series, Vol. XII, No. 68 —August, 1901. 



