OF THE

AMERICAN ACADEMY

OF

ARTS AND SCIENCES.

NEW SERIES.

VOL. XII.

WHOLE SERIES.

VOL. XX.

FROM MAY, 1884, TO MAY, 1885.

SELECTED FROM THE RECORDS.

BOSTON:

UNIVERSITY PRESS: JOHN WILSON AND SON.
1885.

CONTENTS.

PAGE

I. A Revision of the North American Species of the Genus

Oxytropis, DC. By ASA GRAY

1

II. Notes on some North American Species of Saxifraga. By Asa

GRAY

8

III. A Contribution to our Knowledge of Paleozoic Arachnida. By

SAMUEL H. SCUDDER.

13

IV. On the Development of some Pelagic Fish Eggs.- - Preliminary

Notice. By ALEXANDER AGASSIZ and C. O. WHITMAN .

-

23

V.

The External Morphology of the Leech. By C. O. WHITMAN

VI. On the Anatomy and Histology of Aulophorus Vagus. By

JACOB REIGHARD

76

88

VII. Descriptions of New Species of Cambarus; to which is added a

Synonymical List of the known Species of Cambarus and

Astacus. By WALTER FAXON

VIII. A Method of Measuring the Absolute Sensitiveness of Photo-

graphic Dry Plates. By WILLIAM H. PICKERING

IX. On the Reduction of Camphor to Borneol. By C. LORING

JACKSON

X. Dictyoneura and the Allied Insects of the Carboniferous

Epoch. By SAMUEL H. SCUDder .

107

159

163

167

XI. The "Taconic System," and its Position in Stratigraphic

Geology. By JULES MARCOU

XII. Contributions to the Botany of North America. By Asa

GRAY

PAGE

174

257

311

XIII. Notes on some Species of Gymnosporangium and Chrysomyxa

of the United States. By W. G. FARLOW

XIV. Contributions to American Botany. By SERENO WATSON. 324

XV. An Examination of the Standards of Length constructed by

the Société Génevoise. By W. A. ROGERS

XVI. A Method of Filtration by Means of Easily Soluble and

Easily Volatile Filters. By F. A. GOOCH

.

379

390

XVII. Observations of Variable Stars in 1884. By EDWARD C.

PICKERING

393

XVIII. A Photographic Study of the Nebula of Orion. By EDWARD

C. PICKERING

407

XIX. Relation between Superficial Energy and Thermo-Electricity.

By CHARLES Bingham Penrose .

417

XX. On the Separation of Titanium and Aluminum, with a Note

on the Separation of Titanium and Iron. By F. A. Gooch 435

XXI. Atmospheric Electricity. By ALEXANDER MCADIE and

AUSTIN L. MCRAE

XXII

The Effect of Temperature on the Magnetic Permeability of

Iron and Cobalt. By JOHN TROWBRIDGE and AUSTIN

L. MCRAE

462

XXIII. Photography of the Infra-Red Region of the Solar Spectrum.

By WILLIAM H. PICKERING.

473

XXIV. Methods of Determining the Speed of Photographic Exposers.

By WILLIAM H. PICKERING

478

XXV. Principles involved in the Construction of Photographic

Exposers. By WILLIAM H. Pickering

483

XXVI. On a New Method for Determining the Mechanical Equiva-

lent of Heat. By A. G. WEBSTER

XXVII. A Standard of Light. By JOHN TROWBRIDGE.

PAGE

490

494