TABLE OF contents; 



ARTICLE I. 



ARTICLE II. 



ARTICLE in. 



Introduction. Pp. 16. 



Advertisement . . . . . . . . iii 



List of Officers of the Smithsonian Institution . . . . ix 



(\o. 240.) Problems of Rotary Motion presented by the GYROscorE, 

 THE Precession of the Equinoxes, and the Pendulum. By Brevet 

 Maj. -General J. G. Barnard, Colonel of Engineers, U. S. A., A.M., 

 LL.D., Member of National Academy of Sciences. 1871-1873. 4to. 

 pp. 7-4. 



The Precession of the Eqnino.xcs and Nutation as resulting from the Theory 

 of the Gyroscope ........ 1 



On the Motions of Freely Suspended and Gyroscopic Pendulums, and on 



the Pendulum and Gyroscope as exhibiting the Rotation of the Earth . 15 



On the Internal Structure of the Earth considered as affecting the Phe- 

 nomena of Precession and Nutation . . . . .33 



New Addendum ........ 42 



(No. 241.) A Contribution to the History of the Fresh-Water Alg^ 

 OF North America. By Horatio C. Wood, Jr., M.D., Professor of 

 Botany, and Clinical Lecturer on Diseases of the Nervous System in 

 the University of Pennsylvania; Physician to the Philadelphia Hospital, 

 etc. October, 1872. 4to. pp. 274. Twenty-one colored plates. 

 Preface . . . . . . . * . . v 



Introduction ........ 1 



Fresh-Water Algas of the United States ..... 9 



Class Phycochromophyceae ...... 9 



Order Cystiphora3 ...... 10 



Family Chroococcacese . . . . . .10 



Order Nematogeneaj . . . . . .15 



Family Oscillariacese . . . . . .16 



Family Nostochaceaa ...... 23 



Family Rivulariaceae ...... 43 



Family Scytonemacese . ..... 55 



Family Sirosiphonacese ...... 67 



Class Chlorophyllaceae ...... 77 



Order Coccophycese ...... 73 



Family Palmellacea; . '. . . . .78 



Family Protococlacese ...... 85 



Family Volvocinea; ...... 98 



Order Zygophyceae . . . . . .100 



Family Desmidiacese . . . . . .100 



Family Zygnemacese . . . . . .169 



' Each memoir is separately paged and indf xed. 



