616 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
Page. 
Numbers, Square, whose sum is a square. 580 
— Sum of two biquadrate, cannot be a biquad¬ 
rate number. A. Martin. 609 
Obituary notices. 465, 520, 529 
— Report of committee relative to. 518 
Observation of sudden phenomena. S. P. 
Langley.41, 531 
Obsidian, Spherulitic crystallization in. J. 
P. Iddings. 568 
Occupation, Reported, of o Tauri by Saturn 
in 1679. G. W. Hill. 606 
Officers of the Mathematical Section. See 
Mathematical Section. 
Officers for 1889... 527 
- 1890 . 548 
-1891 .. 562 
- 1892 . xvii 
Ogden, H. G.: Chart-making. 554 
— Distortion in plane-table sheets.... 508 
Osborne, J. W.: Surfaces feebly sensitive to 
light. 518 
Parker, Peter, Death of... 502 
— Obituary notice of, by W. B. Taylor. 491 
Parry, C. C., Death of. 566 
Peale, A. C.: Obituary notice of F.V. Hayden. 476 
Pendulum apparatus. T. C. Mendenhall. 566 
— Length of Hater’s. O. H. Tittmann. 553 
— observations, Reduction of. E. D. Pres¬ 
ton ... 115, 541 
— Study of earth’s figure by. E. D. Preston. 567 
Penokee iron-bearing series of rocks. C. R. 
Van Hise. 530 
Personal equation, Elimination of, from stel¬ 
lar transits by photography. F. H. Big¬ 
elow. 570 
-Observation of sudden phenomena. S. 
P. Langley ... 41, 531 
-Some peculiarities in. J. R. Eastman. 515 
Perturbations of the minor planets. W. F. 
McK. Ritter. 604 
— Secular, of two planets moving in the 
same plane, with application to Jupiter 
and Saturn. 608 
Philosophy and specialties. President Mal- 
lery’s address. 1 
Physics, Fundamental, Concepts of. S. New¬ 
comb.. 514 
Plane-table sheets, Distortion in. H. G. Og¬ 
den. 508 
Plant life, Formation of deposits of lime, 
iron, and silica by. W. H. Weed. 537 
Pohle, J., elected member. 555 
Powell, J. W.: Evolution of industry. 569 
— Laws of eorrasion. 519 
Predictions, Estimation of skill in making. 
G. K. Gilbert. 582 
President’s address. See Address. 
Page. 
Preston, E. D., elected member. 520 
— Reduction of pendulum observations 115, 541 
— Study of the earth’s figure by means of 
the pendulum. 567 
Prisms, New metric system of numbering. 
S. M. Burnett.... 566 
Probabilities, Failure of the apparent law of. 
H. A. Hazen. 581 
— A. Martin. 602 
— M. H. Doolittle.:. 583 
— Problem in. A. Hall. 605 
-M. H. Doolittle. 602 
— Two problems in. M. H. Doolittle. 605 
Probability equations. M. H. Doolittle. 603 
— of an event resting on the concurrent tes¬ 
timony of two witnesses, Application of 
a formula for. M. H. Doolittle. 604 
Probable error, Short, rough method of com¬ 
puting. C. H. Kummell. 608 
Problem-solving. A. Hall.!. 598 
Proper motions, Assumption and fact in the 
theories of solar and stellar. J. R. East¬ 
man . 143 
Puma, Epitome of the natural history of. F. 
W. True. 554 
Quaternion, What is a? A. S. Christie. 579 
Quartic, New simple and symmetrical solu¬ 
tion of. C. H. Kummell. 609 
Quartz, Origin of primary, in basalt. J. P. 
Iddings. 515 
— Porphyritic, in eruptive rocks. J. S. Dil- 
ler. 531 
Railway systems of England and America, 
Origin of. 533 
Rainfall, Trans-Mississippi. A. W. Greely.. 505 
— Artificial production of. B. E. Fernow ... 557 
— Influence of forests upon. C. Abbe. 521 
-. B. E. Fernow. 520, 552 
Rain-gauge, New self-recording. C. F. Mar¬ 
vin . 502 
Rain-making experiments in Texas. G. E. 
Curtis. 570 
Ramsden’s dividing engine. J. E. Watkins.. 554 
Rathbun, R.: Obituary notice of J. H. Kidder. 480 
Reduction of pendulum observations. E. D. 
Preston. 115, 541 
Refraction by cylinders with axes crossed 
at various angles. S. M. Burnett. 531 
Reid, H. 8 .: Note on the Muir glacier of 
Alaska . 555 
Relative abundance of the chemical ele¬ 
ments. F. W. Clarke. 131 
Religions, Study of, by the methods of nat¬ 
ural history. O. T. Mason. 564 
Resisting medium in space. A. Hall. 606 
Riley, C. V.: Bacteriology in applied ento¬ 
mology. 565 
