PHYSICS — AMES, BARNETT. 245 



PHYSICS. 



Ames, Joseph S., Johns Hopkins University, Baltimore, Maryland. 

 Grant No. 206. Rcdetevmiiiatioyi of standard wave-lengths by inter- 

 ference methods in order to correct Rowland' s ' 'standards. ' ' $1 ,000. 



Abstract of Report. — The fact that Rowland's standards of wave 

 length were inaccurate was clearly proved some years ago — first, by 

 Michelson ; second, by Fabry and Perot. The source of the errors 

 was shown by H. Kayser to be inherent in the "coincidence 

 method" as used in grating measurements. It therefore became 

 necessary to devise a method free from errors and to redetermine the 

 standard wave-lengths. This was done to a certain extent by Fabry 

 and Perot. The measurements are, however, of such importance 

 that it is the opinion of all physicists that their work should be 

 repeated in several laboratories. 



Throughout the entire investigation my assistant was Dr. James 

 Barnes, one of the foremost investigators in this field of work. 



An interferometer was constructed along the general lines of 

 Fabry and Perot's apparatus, but with several improvements. Meas- 

 urements were first made by the visual method employed by Fabry 

 and Perot, but later on experiments were made in the use of photog- 

 raphy. These last were successful so far as they went, and if this 

 year's work shows the accuracy of the method it will open up an 

 entirely new field of research with interferometers. So far very few 

 wave-lengths have been determined, and these agree, within the 

 limits of experimental errors, with those obtained by Fabry and Perot. 



The following results have been obtained, however: (i) The 

 photographic method has been developed ; (2) new forms of spec- 

 trum tubes have been studied, and the best one has been adopted for 

 future use ; (3) various effects which might influence the permanance 

 of the t3'pe of radiation have been studied ; (4) a most careful study 

 of^the theory and adjustments of the interferometer has been made. 



It is planned to make a full study of the photographic method 

 and final measurements of as many wave-lengths as possible. 



Barnett, S. J., Tulane University, New Orleans, L,ouisiana. Grant 

 No. 149. For determining whether an electric inteitsity is devel- 

 oped in a dielectric moving at ri^ht aytgles to a magnetic field. 

 (For first report see Year Book No. 3, p. 124.) $250, 



Abstract of Report. — For a number of reasons no experiments 

 except a few of a preliminary character have been possible during the 

 past year. Work will be carried on in the future at Tulane Univer- 



