ABSTRACTS 



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FHYSICS.— Ionization and resonance potential for electrons in vapors 

 of lead and calcium. F. L. Mohler, Paul, D. Foote and H. M. 

 Stimson. Bur. Standards Sci. Paper 368. Pp. 14, figs. 2. 1920. 



Measurements of electron currents in three electrode vacuum tubes 

 of the type previously described have been made in vapors of lead and 

 calcium. 



The lead and calcium were boiled in porcelain tubes at temperatures 

 of about 1000° and 900°, respectively. Current voltage curves in 

 lead showed a resonance potential of 1.26 volts and an ionization 

 potential of 7.93 volts. Applying the quantum relation Ve = hv we 

 find that 1.26 volts correspond within experimental error to the fre- 

 quency of a strong infra-red spectrum line at X = io,29iA, giving a 

 theoretical value of the resonance potential 1.198 volts. 



In calcium two resonance potentials were found at 1.90 volts and 

 at 2.85 volts of which the first is the most prominent. Ionization oc- 

 curred at 6.01 volts. The ionization potential corresponds to the 

 limit of the principal series 1.5 S, X = 2027, A giving as the theoretical 

 value V = 6.081 volts. The first resonance is determined by the line 

 1.58 — 2p2, X = 6572.78 A, V = 1-877 volts. The second resonance 

 corresponds to the line 1.58 — 2 P, X = 4228.73 A, V = 2.918 volts. 



The spectral relations of the first resonance potential and ionization 

 potential are analogous to the relation found with other metals in this 

 group. Work of other observers shows that both the lines 1.5 S — 2 

 P and 1.5 S — 2p2 appear below the ionization potential in most metals 

 of this group. F. L. M. 



PHYSICS.—^ new interferential dilatometer. Irwin G. Priest. 

 Bur. Standards Sci. Paper 365. Pp. 10, fig. i. 1920. 



This paper describes new instruments and methods for measuring 

 very small changes in the lengths of samples which are too small to 

 be examined by the Fizeau interferential method. Only a single small 

 pin is required as a sample. 



The method of measurement depends upon the change in width of 



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