944 



SCIENCE. 



[N. S. Vol. XIX. No. 495. 



For the present all resistance measure- 

 ments of the bureau are referred to the 

 mean of a number of one-ohm manganin 

 standards which are reverified from time 

 to time at the Physikalisch-Technische 

 Reichsanstalt, and are, therefore, known in 

 terms of the primary mercurial standards 

 of that institution. 



The construction of secondary mercurial 

 standards, which after suitable aging 

 change less than wire standards, has been 

 begun and in time will be of service in 

 fixing with the greatest possible accuracy 

 the value of the one-ohm working stand- 

 ards. It is intended as soon as possible to 

 construct a number of primary mercurial 

 resistance standards. A supply of suitable 

 Jena glass tubing has been secured, but the 

 urgent demands upon the section for test- 

 ing and the limited force available pre- 

 clude this important piece of work for the 

 present. 



The set of manganin resistance stand- 

 ards of the bureau consists of ten one-ohm 

 coils and four coils each of the following 

 denominations : 10, 100, 1,000, 10,000, 100,- 

 000 ; .1, .01, .001, .0001, .00001, besides two 

 two-ohm, three three-ohm, two five-ohm 

 coils and two megohm boxes, this giving 

 in most eases two reference standards and 

 two working standards of each denomina- 

 tion. 



Special efforts have been made to secure 

 the accurate comparisons of the one-ohm 

 coils with those of the other denominations, 

 bearing the ratios of 1, 10, 100, etc. For 

 this purpose as well as for the most ac- 

 curate measurement of 'other resistances. 

 Dr. Wolff designed and had constructed by 

 Otto Wolff, of Berlin, a special mercury 

 contact Wheatstone bridge of the Anthony 

 form. For directly determining the ratio 

 of two nearly equal coils Dr. Wolff had a 

 special set of ratio coils and a four-dial 

 shunt box constructed which enabled the 

 ratio to be read off directly to parts in a 



million, the dials reading respectively .1 

 per cent., .01 per cent., .001 per cent, and 

 .0001 per cent. Other special apparatus 

 has been built or is under way for making 

 precision measurements with a minimum 

 of labor in the observations and computa- 

 tions. 



The legal standard of electromotive force 

 in the United States is the Clark cell, the 

 value of which is 1.434 international volts 

 at 15° C. and is, of course, the value used 

 by the bureau. The Reichsanstalt uses a 

 value nearly 0.1 per cent, smaller, namely, 

 1.4328. This unfortunate discrepancy can 

 only be removed by further action of the 

 next international congress followed by an 

 act of congress if a change is authorized, 

 fixing anew our legal standard. The value 

 1.433 is, perhaps, the nearest value that 

 can be assigned from present data. 



A considerable amount of testing has al- 

 ready been done by this section, chiefly 

 resistance standards and resistance boxes, 

 but including also a variety of other ap- 

 paratus. 



Section 2. Magnetism and Aisolute 

 Measurement of Cwrrewl— Preparations 

 are under way for magnetic testing, but 

 want of laboratory space has retarded the 

 development of this work. Dr. Guthe is 

 carrying on two important researches, 

 namely, a study of the silver voltameter 

 and a redetermination of the electrochem- 

 ical equivalent of silver and of the absolute 

 value of the Weston and Clark standard 

 cells. A new absolute electrodynamometer 

 is to be built for the latter investigation. 

 The results of the investigation of the vari- 

 ous forms of silver voltameters have re- 

 cently been communicated to the American 

 Physical Society. The magnetic laboratory 

 is about to be established, and magnetic 

 testing and research will be developed as 

 rapidly as our limited force will permit. 



Section 3. Inductance and Capacity.— 

 A careful study of mica and paper eon- 



