250 REPORTS ON INVESTIGATIONS AND PROJECTS. 



Carhart, Henry S,, University of Michigan, Ann Arbor, Michigan. 

 Grant No. 157. Preparation of viaterial for standard cells, etc. 

 (For first report see Year Book No. 3, pages 124-126.) $5oo- 



Abstract of Report. — Since the last report extensive changes have 

 been made in the absolute electrodynamometer, which has been used 

 for the absolute measurement of the electric current for the purpose 

 of determining the electromotive force of the Weston normal cell. 

 Serious trouble was occasioned by the unusual elastic fatigue of the 

 particular phosphor-bronze wire employed to support the movable 

 coil. This difficulty has been overcome by employing a longer wire, 

 annealing it in an electric oven, and using a twist of 180° instead of 

 360°. A remeasurement of the coils was made as far as possible, and 

 the results are very gratifying, because they show that no changes 

 of any moment have taken place in the large stationary coil. 



At a conference on electrical units and standards called by the 

 Reichsanstalt to meet in Charlottenburg on October 23, 1905, the 

 Weston normal cell was adopted as a standard in place of the Clark 

 standard cell. It becomes, therefore, all the more important that 

 the electromotive force of the Weston cell should be determined in 

 absolute measure before the meeting of the International Commission 

 late in the autumn of 1906. Results will be reported later on. 



ChildtCIementD.^ColgateUniversity, Hamilton, N.Y. GrantNo. 187. 

 hivestigation of ionizatioyi in the ?ieigkborhood oj a mercury arc in 

 a vacuum. (For first report see Year Book No. 3,p- 126.) $50. 



Abstract of Report. — The following facts have been brought out by 

 this investigation in addition to those reported last year. The space 

 in the tube connected with a mercury arc becomes highly conducting. 

 A luminous space gradually spreads out from the arc, and the front 

 of this region has the greatest luminosity and the highest conduc- 

 tivity. This conductivity is not due to ions coming from the arc, nor 

 to rays sent out by it. It is probably not due to the high temper- 

 ature of the gas. A probable explanation is that when ions recom- 

 bine they are in a condition of unstable equilibrium, much like the 

 atoms of radioactive matter, and often break up again. There is an 

 E. M, F. between electrodes inserted in different parts of the tube, 

 which is possibly due to the more rapid diffusion of the negative ions. 

 Hope was expressed in the beginning of this work that the velocity 

 of the ions in the arc could be determined by a method similar to that 

 used in finding the velocity of ions drawn from a flame, but the method 

 could not be used on account of the ionization in the neighborhood of 

 the arc. 



