VOLUME 56. 



1. Kennf.lly, a. K., and Kuuokawa, K. — Acoustic Impedance and its Measuremeot. 



pp. 1-42. February, 1921. SI. 25. 



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



3. BniDGMAN, P. W. — Electrical Resistance under Pressure, including certain llfpiid 



Metals, pp. 59-154. February, 1921. S1.25. 



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, Gbinnell, and Scmumb, \V. C. — The Potential of the Thallium Electrode and 



the Free Energy of Formation of Thallous Iodide, pp. 197-23G. April, 1921. $1.10. 



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



pp. 237-288. April, 1921. Sl.OO. 



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



June, 1921. $1.25. 



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



$.75. 



10. Cross, Charles R. — The Rumford Fund. Awards of the Premium and Grants for 



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



11. Records of Meetings; Biographical Notices; Officers and Committees; List of 



Fellows and Foreign Honorary Members; Statutes and Standing Voles, etc. 

 pp. 377-445. August, 1921. $.65. 



(Continued on p'i(/e 3 of cover.) 



