(Continued from page 3 of cover.) 



VOLUME 56. 



2. 

 3. 



4. 



5. 



7. 



9. 



Kennelly, a. E., and Kurokawa, K. — Acoustic Impedance and ita Measurement. 



pp. 1-42. February, 1921. $1.25. 

 Bell, Louis. — Ghosts and Oculars, pp. 43-58. February, 1921. $.85. 

 Bridgman, p. W. — Electrical Resistance under Pressure, including certain liquid 



Metals, pp. 59-154. February, 1921. $1.25. 

 LrPKA, Joseph. — Motion on a Surface for any Positional Field of Force, pp. 155-182. 



March. 1921. $1.00. 

 WiLLEY, A. — Arctic Copepoda in Passamaquoddy Bay. pp. 183-196. May, 1921. 



$.75. 

 Jones, Grinnbll, and Schumb, W. C. — The Potential of the Thallium Electrode and 



the Free Energy of Formation of Thallous Iodide, pp. 197-236. April, 1921. $1.10. 

 Heidel, W. a. — Anaximander's Book, The Earliest Known Geographical Treatise. 



pp. 237-288. April, 1921. $1.00. 

 Wheeler, W. M.- — Observations on Army Ants in British Guiana. pp. 289-328. 



June, 1921. $1.25. 

 Hitchcock, Frank L. — The Axes of a Quadratic Vector, pp. 329-331. June, 1921. 



$.75. 



