BUCKINGHAM: REHEAT FACTOR OF TURBINES 147 



The ellipticity dispersion curves appear somewhat similar 

 to those obtained by transmission thru metallic films. For 

 iron, cobalt, and steel the vibration is negative (contrary to the 

 magnetizing current), while nickel, iron and magnetite show 

 anomalous dispersion, the reflected light being plane polarized 

 at wave length of 600mm for nickel and invar, and 520mm for 

 magnetite In all of the substances the ratio of minor to major 

 axes was found to be of an order 10 -3 . It is interesting to note 

 the probable influence of the iron in the invar mirror. The curve 

 closely resembles that obtained for nickel, the points of zero ellip- 

 ticity being identical, but the magnitude of the effect in invar 

 is greater in the negative portion of the curve and smaller in the 

 positive red. Heusler's alloy showed a very slight negative 

 ellipticity too small to admit measurement. The accompanying 

 figure presents several typical ellipticity dispersion curves. 



Curves were also obtained showing the variation of both rota- 

 tion and ellipticity with the magnetic field. The rotation resem- 

 bled the I-B type curves as found by Du Bois. The ellipticity 

 likewise presented this characteristic, and, when intensities of 

 magnetization, easily obtainable from the steep slope and the 

 asymptotic sections of the curve R = f (B), are plotted against 

 ellipticities, the result is a straight line showing a direct propor- 

 tionality, E - FT. 



The work was carried out in the Brace Laboratory of Physics. 

 Lincoln, Nebraska, under the direction of Dr. C. A. Skinner to 

 whom the writer is indebted. 



THERMODYNAMICS.— The reheat factor in steam-turbine 

 design. E. Buckingham, Bureau of Standards. Communi- 

 cated by C. W. Waidner. To appear in the Bulletin of the 

 Bureau of Standards, 7, No. 4. 1911. 

 The expansion line of a multistage steam turbine, drawn on the 



Mother diagram with total heat, H, as ordinate and entropy. 



<p, as abscissa, crosses each isopiestic at an angle with the v 



axis such that 



— X 2 tan/3 = — — 



1 — e 



