The status of the mixture is described in the table.

Professor Harry F. Reid informs me that a continental shelf of the Atlantic Ocean has a very definite slope which is very nearly that obtained for the extremely wet sand in these experiments.

I reserve the mathematical theory for a future paper.

The sand has been meshed by Professor Roys of the Worcester Polytechnic Institute with the following results:

PALÆOMASTODON, THE ANCESTOR OF THE LONG-JAWED MASTODONS ONLY

BY HENRY FAIRFIELD OSBORN

AMERICAN MUSEUM OF NATURAL HISTORY, NEW YORK CITY

Read before the Academy, April 29, 1919

In 19001 the author predicted that the ancestors of the Proboscideans, as well as of the Hyracoidea and some other orders of mammals, would be discovered in Africa. Two years later the members of the British Geological Survey of Egypt discovered in the Oligocene of the Fayûm remains of Paleo

mastodon and of Maritherium, which were at once regarded as the solution of the ancestry of the Proboscideans. These animals took their place in all literature as two steps in the early evolution of this remarkable group.

In 19092 Osborn pointed out that Mæritherium is to be regarded as a terrestrial form of the Sirenians (manatees and dugongs) in no way directly related to the Proboscideans. It now appears that Palæomastodon must also be removed from its generalized position and be regarded as the ancestor of the long-jawed mastodons only; it is far too much specialized in the longirostral direction to be ancestral to the Proboscidea in general. These longjawed mastodons are distinguished by the peculiar use of the front teeth of the lower jaw, which together made a broadly flattened, spoon-shaped tooth,

FIG. 1

Outline of the mounted skeleton of Megabelodon in The American Museum of Natural History, discovered by E. L. Troxell in the Middle Pliocene of Texas. Drawing one fortyfifth natural size.

almost entirely enamel covered. Phases of the evolution of this long-jawed phylum are seen in the classic Trilophodon angustidens of Cuvier, in the lower Miocene of France. A branch reached Texas in the Upper Miocene (Trilophodon productus of Cope), and Florida as well as Texas in the Trilophodon serridens of Cope. It attained gigantic proportions in the Middle Pliocene. The Megabelodon of Barbour, a superb skeleton of a long-jawed and extremely short-limbed Proboscidean, recently discovered in Texas by Mr. E. L. Troxell, has been mounted in The American Museum of Natural History. It represents one of the culminating stages in the evolution of the long-jawed mastodons. In these animals we find proof of nearly direct linear descent from the Pala omastodon of the Fayûm, e.g., the long enamel band on the upper tusks, the broadly spoon-shaped arrangement of the lower tusks with enamel covering. In massiveness these animals parallel and even surpass the true mastodons of the Pleistocene, to which they are only indirectly related.

THE ELONGATION DUE TO MAGNETIZATION

BY C. BARUS

DEPARTMENT OF PHYSICS, BROWN UNIVERSITY

Communicated, April 30, 1919

1. Introductory.-The small longitudinal displacements due to magnetostriction have been frequently subjected to investigation and an excellent summary is given in Winkelmann's Handbuch, vol. 5, p. 307, et seq., 1908. The measurements of Prof. C. G. Knott and his students Nagaoka and Honda are particularly noteworthy. In 19112 my son, Mr. Maxwell Barus, and I used these phenomena for the purpose of testing a peculiar type of interferences then under discussion.

The present purpose is similar, being a test of the contact lever recently3 described.

The elongation (and contraction) phenomena are necessarily complicated by the occurrence of hysteresis loops to which the present paper (in which the measurements are not made by the continuous variation of currents and field, but by successively making and breaking the circuit) will give no attention. This subject has been adequately explored by Professor Knott and the authors cited. The chief interest in this paper is rather the continued increase of the contractions due to magnetization, not only after the latter has practically reached a maximum, but in a marked degree (so far as I have gone, fields up to 800), indefinitely. There is no sure indication of an abatement of the contraction. Hence the magnetic contribution of the present paper is to lie in the treatment in strong fields.

2. Apparatus.-The contact lever shown in figures 1 and 2 of the paper cited was modified as indicated in figure 1, where F is the semicircular fork in a vertical plane, rigidly attached to the bed plate of the interferometer by a strong clutch (not shown), holding the cylinder, g, the handle of the fork. The vertical axis a of the contact lever is secured between the screw pivots b of the fork. The horizontal strip of brass d, rigidly fastened to the center of the axle a, carries at its end the auxiliary mirror mm' of the quadratic interferometer. For this purpose, a short length, f, at the end of d has been bent upward at right angles to d, so that mm' may be held between plates of brass by the yoke-shaped steel clip c. At the side of the lever is a vertical brass plate inset c, to which a small glass plate n has been fastened with cement. It is against this that the conical end of the iron rod rr to be examined, pushes. The spring S attached to the blade d and a lateral projection from the fork F insures continuous contact at a constant pressure.

The iron rod rr originally about 43 cm. long and 67 cm. in diameter, is enveloped by a tubular water jacket ww. Through this a current of water entering at t and leaving at t' is kept flowing from a large copper Mariotte flask about 50 cm. high and 30 cm. in diameter, and containing water at the tempera

!

ture of the room. Two such flasks were at hand to be used alternately. The coil CC 26 cm. long and 3.7 cm. in external diameter, is wound immediately on the tubular water jacket.

The rod rr fits the tube ww loosely and is centrally detached at the remote end by aid of a bushing s and a small bolt. The front end is free. The coil CC is held in position by a large clutch (not shown) encircling it at the middle and attached to the bed plate of the interferometer. It is additionally attached at the tubulures t and t'. Finally the conical end M of a micrometer screw (also rigidly attached to the bed plate) gives the remote end of the rod rr any desirable fiducial position. This micrometer M has the further advantage of permitting an independent standardization of the contact lever, as there is obviously always sufficient elastic yielding in the apparatus to considerably shift the interference fringes.

=

In the experiments made, the breadth of the ray rectangle mm' of the interferometer was b 9.7 cm.; the normal distance between the rod rr and the axis a, 7 cm.; the length of the contact lever a to mm', 10.6 cm.; and the length of the axle a, 10 cm.

3. Observations.-The helix C in figure 1 was slender in shape, the length being 37 cm. and the diameter within being about 1.5 cm. There were about 11.2 turns per centimeter per layer and 8 layers of wire so that the field within may be estimated at H = 110 i gauss, i being the current in amperes. The current 0.01 to over 8 amperes thus corresponded to field from 1 to over 800 gauss.

The first rod selected was of low carbon shop steel 43 cm. long, so that it projected a few centimeters beyond either end of the helix.

The displacement of fringes observed was characteristic, being (in the smaller fields) slow and deliberate on closing the circuit (so that their motion could almost be followed by the eye), but very rapid on breaking the circuit. The experiments were begun with small fringes (about 0.1 mm. in the ocular), and the readings Ae were made in terms of an ocular micrometer scale which was a centimeter divided into 0.1 mm. This was compared with the datum, AN, of the displacement micrometer normal to one of the mirrors of the interferometer.

If AN corresponds to the angular displacement, A0, of the contact lever and to Al of elongation of the iron rod r in the helic C (figure 1) we may write as above

if i is the angle of incidence (45°) at the mirrors of the interferometer and b the breadth of the ray parallelogram. But

if r is the normal distance of the line of thrust of the rod rr from the axis of the contact lever. Thus

If I is the length of the iron rod Al/l will be the datum required.

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