(Continued from, page 3 of cover.) 



VOLUME 56. 



1. Kennbxly, a. E., and Kurokawa, K.— Acoustic Impedance and its Measurement. 



pp. 1^2. February, 1921. $1.25. 



2. Beix, LoDts.— Ghosts and Ocul'irs. pp. 43-58. February. 1921. $.85. 



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



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



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



March, 1921. $1.00. 



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



$.75. 



6. Jones, Grinnell, 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. 



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



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



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



June, 1921. $1.25. 



9. Hitchcock, Frank L.— The Axes of a Quadratic Vector, pp. 329-351. June, 1921. 



$.75. 

 10. Cross, Chables R. — The Rumford Fund. Awards of the Premium and GranU for 

 Research in Light and Heat. pp. 353-373. July, 1921. $.45. 



