48 Chemistry and Physics 



No. 249. (Part IV.) Displacement Interferometry by the aid of the Achromatic 

 Fringes. Octavo, 172 pages, 117 figs. Published 1919. Price $2.00. 



Anomalies observed in the last report, in treating the elastic deformations of 

 small bodies on the interferometer, led to the construction of the contact lever, 

 using achromatic fringes as described in the first chapter. The contact lever is 

 modified (Chapter II) for the interpretation of the elastic discrepancy specified. 



A different application of the contact lever is described in Chapter III, and 

 particular attention is given to the occurrences in strong magnetic fields. 



An instrument which lends itself with equal facility to the measurement of 

 thermal expansion and to the determination of elastic moduli is in a measure 

 self-contained for the solution of many thermodynamic problems. Projects of 

 this kind are discussed in Chapter IV. 



Chapters V and VI contain contributions to the electro-dynomometry of 

 very weak (telephonic) alternating currents. The measurement is first made by 

 means of the vibrating telescope, the vibrator of the telephonic system carrying 

 the objective. The sensitiveness is increased upwards a hundred-fold by placing 

 the instrument on the displacement interferometer adjusted for achromatic fringes. 

 The reading is made with a vibration telescope, synchronized with the alternating 

 current in the primary and with the objective vibrating normally to the displace- 

 ment of fringes. Both the amplitude and the phase of the induced current are 

 given by the form of the vibration ellipses obtained, whether modified by re- 

 sistance, inductance, or capacity. Quivering stray magnetic fields in the room 

 may be compensated by the primary solenoid (for instance) almost as easily 

 as the needle of an astatic galvanometer. 



Chapter VII shows that a slight but essential modification of a form of 

 interferometer used by Michelson and Morley makes this apparatus virtually self- 

 adjusting, while satisfying many of the requirements of displacement inter- 

 ferometry. A possible design of this kind for measuring the Fresnel coefficient 

 is tested with a promising outcome in Chapter VIII. 



An interesting class of interferences obtained by superposing the dispersion 

 fringes on identical inclination fringes is discussed in Chapter IX. 



A number of results incidental to the preceding work are collected in Chapter 

 X, which treats of evidences of continuous micrometric convection currents 

 within liquids, the satellites of the achromatic fringes, and peculiarly brilliant 

 phenomena obtainable in connection with Herschel's fringes. 



Chapters XI and XII return to certain gravitational experiments begun in 

 the last report. In Chapter XI the deviations of the horizontal pendulum are 

 read off by the displacement of achromatic fringes. Chapter XII is a continua- 

 tion of the endeavor to follow the actual motion of a gravitation needle, under 

 periodic gravitational attraction. 



No. 153. KING, ARTHUR S. The Influence of a Magnetic Field upon the Spark 

 Spectra of Iron and Titanium. Quarto, in-}-66 pages, 6 plates, 3 text 

 figures. Published 1912. Price $1.50. 



The investigation covers the effect of a magnetic field upon 1,120 lines in the 

 iron and titanium spectra between the limits X 3660 and A. 6743, with discussion of 

 experimental methods, brief historical treatment, and full discussion of the results 

 with reference both to existing theories of the Zeeman effect and the effect of other 

 physical conditions upon spectra. A large portion of the range of wave-length 

 examined has not been covered in previous work with the magnetic field, while the 

 high dispersion employed and the attention to the weaker lines give much new data 

 for those parts of the spectrum already treated to some extent. The large range of 

 wave-length has made it possible to study the change of the average separation of 

 Zeeman components with increase of wave-length, bringing out the important result 

 that for both spectra the average separation increases with the square of the wave- 

 kngth. The material shows clearly how generally the separations, both simple and 

 complex, are related to a fundamental interval involving the accepted value of e/m. 

 Fifty-seven lines having five or more clearly resolved components are examined with 



