the same always when the zincs and bismuths are exchanged. This adjustment is made by gently tapping with a very small hammer one or both projecting ends of the rod c, or driving either cylinder, as indicated, further onto its rod with a block of soft wood until the desired over-all dimension is obtained, indicating a standard (though much smaller) double radius. In making this adjustment for the following experiments the most patient care was exercised, and a micrometer caliper of high precision was used.

The driving clock had been running about two months since winding when the experiments hereafter detailed were made, yet the amplitude of the new pendulums was much greater than necessary to unlock the escapement. One tooth of the "scape-wheel" was marked, and this came round to a certain definite position every five minutes by the face hands of the clock, indicating 40 gyrations of the pendulum. Thus the clock was used as an accurate and dependable counter of pendulum gyrations. A good watch was kept always in the same position beside the clock to measure elapsed time, and always wound at the beginning of an experiment. Room temperature remained nearly constant throughout the experiments. A glass hood always covered the clock to keep out air drafts. Runs of 22 to 24 hours were usually made, to average up irregularities in watch and clock rates. Total elapsed time in seconds was divided by the counted number of gyrations to get the periods in seconds of a single gyration.

Many preliminary experiments were made to detect lack of homogeneity in any cylinder, if such existed. To this end each cylinder was separately turned about-its inner element made the outer-or its upper end the lower. In no case was there any observable change of period. The matter of unequal air resistance of the two pairs of cylinders was gone into quite extensively. Of several attempts to equalize this, the following was found the most trustworthy. A pair of short hollow cylinders of thin firm paper, closed at one end, and of such diameter as to slip snugly on the upper ends of the bismuth cylinders were prepared. These cylinders or caps were pushed just far enough down on the bismuth cylinders to make them equal the zinc cylinders in height, plus thickness of

Proc. Amer. PHIL. SOC. VOL. LX, E, DEC. 20, 1921.

the paper cylinder ends. The performance of the bismuth cylinders thus equipped was carefully compared with that of the zinc cylinders wearing the same paper caps pushed down to contact. Of course, the paper caps, because of their weight, slightly increased the periods of both zinc and bismuth cylinders. But, within the limits of experimental error, it increased them equally, thus showing no effect from the equalization of air resistances. Hence the paper caps, apparently serving no useful purpose, were not used in the following experiments.

Table III. embodies the results of a series of experiments with the zinc and bismuth cylinders on the torsion pendulum. Each period is computed from a run of 22 to 24 hours. All the observed periods are given-not those selected from a larger number.

All bracketed periods were obtained with one setting of the cylinders. After one period or set of periods was observed with either pair of cylinders, these were removed from the pendulum frame and the other pair substituted. This involved each time a new and very careful adjustment of the radii of gyration as before explained.

It is seen that the bismuth pendulum had the shorter period by one part in 1333. This is a very gratifying confirmation in kind of the earlier gravity pendulum findings.

It is also extremely interesting to note that the weight-mass difference between bismuth and zinc appears to be many times greater (350001333) when the mass is measured by the accelerating force of a steel spring than when it is measured by the accelerating force of gravity as in the former pendulum experiments. This is very suggestive and will be discussed in a future paper. Of course, these relative values are only rough first approximations; but their difference is very much too large to be attributed to experimental

errors.

More torsion-pendulum experiments are in progress, and all, thus far, confirm the above findings. A pair of pure silver cylinders are being prepared to compare both with the zinc and with the bismuth

ones.

Although the three distinctly different lines of experiment detailed herein loyally support each other, I hesitate to draw general conclusions from their (to me) astonishing results until after much further experimentation for additional data, and much more time for reflection.

I am greatly indebted to Charles F. Brush, Jr., for efficient aid in preparing the apparatus described, in reducing observation data and in making computations.

CLEVELAND, April, 1921.

ROSE ATOLL, AMERICAN SAMOA.

BY ALFRED GOLDSBOROUGH MAYOR.

(Read April 22, 1921.)

His Excellency the late Commander Warren Jay Terhune, U. S. N., then Governor of Samoa, was so kind as to invite me to accompany him on the U. S. S. Fortune to visit the little known Rose Atoll in S. Lat. 14° 32', W. Long. 168° 12', and we spent twenty-four hours upon this island from June 5 to 6, 1920. There has been no scientific account of the island since 1839.

The island is an atoll, the lagoon being encircled by a narrow ring of limestone composed chiefly of lithothamnium, which is everywhere nearly awash at low tide, excepting on the northeast side, where there is a narrow entrance about six to nine feet in depth, out of which a current constantly flows. The ring of limestone which surrounds the lagoon is quite uniformly about 500 yards in width, while the central lagoon is about two miles wide and appears to have a maximum depth of not more than eight fathoms. There are only two small islets upon the atoll rim, Sand Islet and Rose Islet. The only map of the atoll is U. S. Hydrographic Chart of the Samoan Islands No. 90, based on the survey of the U. S. Exploring Expedition in 1839. This shows Rose Islet as occupying the entire width of the atoll rim, whereas at present it is confined to the inner half of the width of the reef rim. Moreover, this chart shows trees covering the entire area of the islet, whereas at present only the southern half of the islet bears trees. The chart states that Rose Islet is 33 feet high, but at present the land of the islet is 11 feet above high tide, and the tallest trees, as measured by means of a sextant, are about 80 feet high, and thus the total height of the landfall as seen from the ocean is about 90 feet.

Rose Islet is at present about 240 yards S.S.W.-N.N.E., and about 200 yards wide. The southern and southeastern half of the islet is densely covered with a forest composed exclusively of

Pisonia grandis trees, casting so complete a shade that no other plants grow beneath them, save only a single cocoanut palm, which was probably planted by Governor Tilly's party about fifteen years ago. This forest forms a nearly symmetrical dome, the leaves and branches on its confines extending quite to the ground. The largest trees are near the southern end of the grove, and about three feet above the ground one of these trees had a girth of 25 feet 7 inches, and was about 80 feet high. The ground under these trees is covered with a rich chocolate-colored humus, which is of considerable depth near the southern end of the grove.

Apart from this grove of pisonia trees and a half dozen cocoanuts planted by Governors Tilly and Terhune in 1902 and 1920, there are only two other species of plants upon the islet. These have been identified by Professor William A. Setchell and are a pink-flowered creeping Boerhaavea diffusa with stems rarely more than 3 feet long; and a thick-stemmed succulent Portulaca n. sp. with small yellow flowers. Both of these plants grow fully exposed to the sun on the coral breccia and calcareous sand which surrounds the pisonia grove, and none are found under the shade of the trees.

On the south side of Rose Islet the sand beach is reduced to from 1 to 5 feet in width at low tide, and cliffs of coquina from 5 to 8 feet high front the sea. A few feet inland this rocky ledge rises to a height of about II feet above high tide level. The pisonia grove appears to be confined to this region of coquina rock and does not appreciably extend out over the loose calcareous breccia which has been washed in upon the islet in time of storm.

The tree-covered rocky center of the islet is composed of a coquina consisting chiefly of wave-worn fragments of lithothamnium, and also rare and occasional pieces of broken coral such as Favites, Porites, Symphyllia, Pocillopora, and still more rarely Acropora. Imbedded in it are many wave-worn half-valves of Tridacna, and Gasteropod shells, and spines of Echini such as Cidaris were found, as was also the much-corroded ulna and part of the skull of a small Cetacean about the size of a black-fish, the latter being embedded in the coquina about 8 feet above high tide level. A large amount of organic matter dark brown in color and derived