170 



SCIENCE. 



[N. S. Vol. XXI. No. 527. 



I have been engaged, with the assistance 

 of Mr. Grover, Dr. Lloyd and several other 

 members of the bureau, in the absolute 

 measurement of electric capacity and in- 

 ductance and in the investigation of elec- 

 trical measuring instruments, more espe- 

 cially for the precise measurement of al- 

 ternating current, voltage and energy. 

 These investigations have involved the con- 

 struction of much new apparatus, as well 

 as the thorough study of some well-known 

 instruments. One of the practical prob- 

 lems in connection with the accurate meas- 

 urement of capacity or inductance is the 

 determination of the frequency of the in- 

 terrupter or of the alternating current em- 

 ployed. This usually amounts to obtain- 

 ing the speed of some kind of motor, often 

 an electric motor. For some kinds of work, 

 to be within one per cent, is considered suf- 

 ficiently accurate. For other eases one 

 tenth of one per cent, is none too good. 

 In still others one hundredth of one per 

 cent, is deemed necessary. In this work 

 we sought to get the frequency to a thou- 

 sandth part of one per cent. This re- 

 quired a very perfect control of the speed, 

 and yet by attention to all the sources of 

 disturbances, and by the use of a very 

 sensitive indicator, the desired result was 

 obtained and an important additional step 

 taken in absolute measurements. 



Many other interesting and important 

 questions are being investigated, and work 

 enough for years is already before us. 

 These particular examples of the work at 

 the bureau have been cited, not because I 

 presume that you are especially interested 

 in the problems themselves, but rather to 

 illustrate the kind of research work we are 

 doing. 



The work of testing is being carried on 

 at the same time. Resistance standards, 

 current standards, standard cells, wheat- 

 stone bridges, potentiometers, magnetic in- 

 struments, current instruments, voltmeters. 



wattmeters, condensers, inductances and 

 many other electrical instruments have 

 come to us from manufacturers, universi- 

 ties, technical laboratories and departments 

 of the uational government. To be abie 

 to get reliable standards and to have in- 

 struments calibrated at a nominal cost is 

 a boon to all careful experimentalists. 

 Heretofore it has often happened that the 

 burden of the work in a given investigation 

 has been to calibrate the instruments em- 

 I^loyed, and often the facilities at com- 

 mand were insufficient to yield results of 

 high accuracy. Within the last three years 

 (that is, since the bureau has been testing 

 instruments) there has been a marked im- 

 provement in the quality of some kinds of 

 electrical instruments made in this coun- 

 try. It is now so easy to determine whether 

 a resistance box guaranteed by the maker 

 to be correct to one fiftieth of one per cent, 

 fulfils the guarantee, that the maker is 

 compelled to use correct standards and to 

 adjust his resistances carefiilly in accord- 

 ance with the same. 



Probably the most interesting collection 

 at the St. Louis Exposition from the stand- 

 point of physical science was the magnifi- 

 cent exhibit of scientific instruments made 

 by Germany. There was a time not so 

 very long ago when France and England 

 surpassed Germany in the production of 

 scientific instruments. But the giant 

 strides which Germany has made in the 

 last twenty years has left other countries 

 in the rear, and this wonderful progress 

 has been largely due to the wise encourage- 

 ment and assistance offered to instrument 

 makers by the German government. This 

 assistance has taken various forms, but the 

 principal factor has probably been the work 

 of the Reichsanstalt and the Normal Aich- 

 ungs Kommission, the two government 

 laboratories doing the work which the bu- 

 reau of standards aims to do in the United 

 States. They have set a high standard for 



