540 



SCIENCE 



[N. S. Vol. XLITI. No. 1111 



SYMPOSIUM ON THE EXPLORATION OF THE PACIFIC 



Arranged by W. M. Davis 

 (By invitation of the Program Committee) 

 On Exploration of the Pacific: W. M. Davis. 



Tlie unsolved problems of the Paeifio can not 

 be settled by a continuation of independent and 

 short-lived explorations, such as have heretofore 

 been undertaken. Future work should be broadly 

 areal, rather than local as on single islands, or 

 linear as in single voyages. It should be con- 

 tinuous through ten or twenty years, so that its 

 seientifie directors may repeatedly inspect the un- 

 certain elements of their work^ and thus gain in 

 the earlier years the expertness necessary for the 

 critical study of the most difficult problems 

 through the later years of their explorations. The 

 type of investigation needed in various branches 

 of science is furnished by the repeated traverses 

 of the Pacific on many interwoven routes in the 

 course of the magnetic survey of the earth by the 

 Carnegie Institution of Washington. Problems 

 of a century or more ago were bravely attacked in 

 adventurous voyages of discovery. Problems of 

 a generation ago were earnestly approached by 

 less adventurous and more scientific voyages of 

 investigation. But the demands of modern science 

 have become exacting. So delicate are the varia- 

 tions of temperature and density in ocean water 

 at various depths, so elaborate are the phenomena 

 of oceanic and atmospheric cireulatioUj so com- 

 plicated are the details of shoreline features by 

 which changes in the level of the land or reversed 

 changes in the level of the ocean are to be in- 

 ferred, so involved are the biological problems of 

 pelagic islands, that the detached facts of earlier 

 scientific voyages must now be supplemented by 

 more continuous bodies of facts. The develop- 

 ment of a comprehensive plan for the exploration 

 of the Pacific is worthy of the National Academy 

 of Sciences, and it is to be hoped that the com- 

 mendation of such a plan by the Academy may 

 lead in the next five or ten years to its realiza- 

 tion. 

 The Importance of Gravity Observations at Sea in 



the Paeifio: J. F. Hayford. 

 A New Metlwd of Determining Gravity at Sea: 



L. J. Bkigos. 



The method employed in measuring g at sea 

 consisted in observing the height of a mercurial 

 column in vacuo necessary to maintain a confined 

 mass of gas at a constant volume when kept at a 

 constant temperature. The mercurial column is 

 contained in a capillary glass tube bent into a 

 zigzag or spiral above the gas chamber, and ex- 

 panding at the top of the capillary into an evacu- 



ated observing bulb which contains a fixed iron 

 point. The capillary tube is sealed through the 

 upper end of the gas chamber, the lower end of 

 the capillary tube dipping beneath mercury in the 

 bottom of the chamber. The pressure of the 

 nitrogen in the gas chamber (about 72 cm.) is so 

 adjusted that at the temperature of melting ice 

 the mercury surface at the top of the column is 

 in contact with the fixed point at the center of the 

 evacuated bulb. The gas chamber is then sealed. 

 The zigzag in the glass capillary makes it possible 

 to raise or lower the observing bulb slightly with 

 reference to the gas chamber, the motion being 

 controlled by a micrometer screw mounted on the 

 gas chamber. In making an observation, the ap- 

 paratus is adjusted to a vertical position in a 

 bath of melting ice, and the observing bulb is 

 raised or lowered until the mercury is in grazing 

 contact with the fixed point. Under these condi- 

 tions the quantity of mercury in the observing 

 bulb is always the same, so that the quantity of 

 mercury in the gas chamber is also constant. The 

 gas volume is therefore constant and the measure- 

 ments are made at constant pressure. The rela- 

 tive value of g at two stations is therefore in- 

 versely proportional to the height of the mer- 

 curial column at these stations. The height is 

 represented by the micrometer reading plus a con- 

 stant term determined from a manometer con- 

 nected with the gas chamber at the time of seal- 

 ing. On shipboard the ice tank is hung in 

 gimbals which are suspended from spiral springs. 

 The apparatus has been used in measurements 

 from Sydney to San Francisco, and from New 

 York to San Francisco, via Panama. The mean 

 probable error of observations at base stations 

 during the latter voyage, in which three instru- 

 ments were used, was 1 part in 60,000. Ap- 

 parent anomalies were observed at sea on both 

 sides of the Isthmus of Panama, along the coast 

 of Lower California and off the California coast 

 near San Francisco. 



The Problem of Continental Fracturing and Dias- 

 trophism in Oceanica: C. Schuchert. 

 A presentation of the problems connected with 



Oceanica, the most mobile region of the Pacific 



Ocean, and with the fracturing and foundering 



of Australasia within the area. 



Petrological Problems in the Pacific: J. P. Id- 

 dings. 



A number of geological problems of the first 

 magnitude are also petrological ones since they 

 involve the material of the lithosphere, which is 

 only known through a study of the rocks. 



