scope when set into rotation. The first to see this, as well as the first to see any relation between magnetism and angular momentum, appears to have been Maxwell, who constructed apparatus for experiments on the subject as early as 1861.

In Maxwell's apparatus an electromagnet was pivoted in a circular frame in such a way as to be free to rotate about a horizontal line through its center of mass and perpendicular to its magnetic axis. With the magnetic axis making an angle with the vertical, the frame was rotated at high speed about a vertical axis, also passing through the magnet's center of mass, and observations were made for a change in 0, stability having been secured by suitable adjustments of the principal moments of inertia. No change could be detected, but only rough observations were possible.

In the experiments on magnetization by rotation Maxwell's electromagnet is replaced by each one of the countless multitude of molecular magnets of which the magnetic body is constituted, and the total change in the orientations of all these magnets with reference to the axis of rotation of the body is determined magnetically.3

on large iron rods by a method depending on the principles of electromagnetic induction; the second, on smaller rods of iron, cobalt and nickel, by the method of the magnetometer. Recently a few preliminary experiments have been made on Heusler alloy.

Some of the essential parts of the apparatus used in the first investigation are shown in the diagram of Fig. 3.

Two nearly similar rods of steel shafting A. and B were mounted with their axes horizontal and perpendicular to the magnetic meridian, and two similar coils of insulated copper wire were mounted about their centers. These coils were connected in series with one another and with a Grassot fluxmeter, which was the principal measuring instrument, and were oppositely wound so that that any variations in the intensity of the earth's magnetic field acting in the same way on both rods might produce

in part of the work, and by an air turbine in the rest.

In making observations fluxmeter deflections were obtained for each of several speeds, first with the rotation in one direction and then with the rotation in the other direction.

After making a great variety of tests, and after taking many precautions to eliminate sources of error, two effects stood out very clearly as the result of the observations, instead of the one which was looked for.

If the mean of the two deflections for the same speed is plotted against the square of the speed, the resulting graph is a straight line as shown in Fig. 4. The mean deflection is thus proportional to the square of the speed. This deflection is due to the increase of the residual magnetic flux through the rotor produced by its centrifugal expansion during rotation-an effect which was not foreseen, and which was

no effect on the fluxmeter. One of the rods, which will be called the compensator, as A, remained at rest; while the other, called the rotor, as B, was alternately rotated and brought to rest, the change of flux being determined by the fluxmeter, which, together with the other apparatus, was standardized by proper subsidiary experiments. For use in these experiments the rods A and B were uniformly wound with solenoids of insulated wire.

To prevent possible disturbances arising from the presence of the earth's magnetic field, the rotor was surrounded by a large electric coil which approximately neutralized the earth's intensity in the region occupied by the rotor.

The rotor was directly driven in either direction at will by an alternating current motor

SPEED IN RPS20 FIG. 5.

and they have since published additional experiments. Very recently another investigation of this converse effect has been made by J. Q. Stewart. All these investigations are indirect but excellent confirmations of the work described here.

In the second investigation, as already stated, the method of the magnetometer was used. A diagram of important parts of the apparatus is given in Fig. 6.

The rod under test, or rotor, F, was mounted with its axis horizontal and normal to the magnetic meridian, as in the first investigation, and in the second, or equatorial, position of Gauss, which offered great advantages over the first, or polar, position for this work.

The magnetometer system, which was astatic, is shown suspended from the torsion head A by

compensating accurately the earth's intensity with the large electric coil E, as in the earlier investigation. C is a small electric coil in series with E to make the zero and sensibility approximately independent of the compensating current in the coil E.

The rotors were driven by an alternating current motor, operating at the same speed in both directions. Three different speeds of the rotor could be obtained by using cone pulleys.

The principal magnetometer observations consisted in getting the double deflections produced by reversing the direction of the rotation, the speed for the two directions being the same. From these readings, the speed, and the calibration experiments, H, could be found as a

function of N. Numerous precautions were necessary as in the earlier investigation.

The results of the observations on four rotors are given in Table I. The "set" of observations there referred to contained four readings, or two double deflections.

With nickel and cobalt observations were made at more than one speed; and H/N was found to be independent of the speed, within the limits of the experimental error, as in the earlier experiments with iron. It is also seen to be independent of the size and shape of the body in rotation, which is an implicit requirement of the theory developed above.

The value of H/N is in all cases negative, but less in magnitude than that of the standard value of 4 π m/e=7.1 e.m.u. for negative electrons in slow motion, as was the case in the earlier experiments with iron, which gave 3.6 and 3.1 in place of 7.1. In view of the experimental errors, it still seems to me doubtful whether these discrepancies indicate definitely that in addition to the negative electrons in orbital revolution there are also positive electrons revolving in orbits. The probability of the presence of the latter orbits is great from the known expulsion of a particles with great velocities from radio-active sub

stances. There can be no question, however, that the effect of the negative electrons is at least greatly preponderant.

A few preliminary results, not of a precise character, but consistent with those of Table I., have been obtained with a rotor of very soft iron and with a rotor of Heusler alloy-a magnetic compound of aluminum, copper and manganese in atomic proportions.

In summing up the chief results of the two investigations it may be said that, in addition to revealing a second and entirely new method of producing magnetization in magnetic substances, they have proved in a direct and conclusive way, on the basis of classical dynamics alone and without dependence on the still obscure theory of radiation, (1) that Ampèreian currents, or molecular currents of electricity in orbital revolution, exist in iron, nickel, cobalt and Heusler alloy; (2) that all or most of the electricity in orbital revolution is negative, or at least that the effect of the negative electricity is preponderant; and (3) that this electricity has mass or inertia. Furthermore, if we admit the classical theory of radiation, according to which a ring of electrons moving in a circular orbit must continually emit energy, but at a smaller rate the more uniformly the electricity is distributed in the ring, we must conclude that the electrons are closely packed in the Ampèreian orbits. For the existence of residual or permanent magnetization proves that these orbits are essentially permanent and can not therefore emit energy at an appreciable rate.

THE OHIO STATE UNIVERSITY

S. J. BARNETT

THE ORIGIN OF THE PINK BOLLWORM

THE determination of the original habitat of the pink bollworm (Pectinophora gossypiella Saunders) is of great interest in relation to. the present distribution of this insect and may be of importance later as indicating where parasitic or other natural checks may be found. A scrutiny of the records gives strong support to the theory that this insect originated in Southern Asia, probably India.

The first account of the insect by W. W.

Saunders1 in 1842 accompanying its original description is based on specimens received from India, and the only information now available in relation to these specimens is an extract quoted by Saunders from a letter from a certain Dr. Barn, superintendent of the Government Cotton Plantations at Broach (Baruch) in western India. This extract is short and significant and is here given in full:

The inclosed is an insect which was very destructive to the American cotton which was sown here (Broach), on light alluvial soil. The egg is deposited in the germen at the time of flowering, and the larva feeds upon the cotton seed until the pod is about to burst, a little previous to which time it has opened a round hole in the side of the pod for air, and at which to make an exit at its own convenience, dropping on the ground, which it penetrates about an inch, and winds a thin web in which it remains during the aurelia state. Curiously enough, the cotton on the black soil was not touched by it. The native cotton is sometimes affected by it.

This letter was addressed to a certain Dr. Royle who forwarded the specimens with this quotation from Dr. Barn to Mr. W. W. Saunders. In relation to this quotation, Mr. Saunders makes this significant comment:

It is interesting to remark that the cotton grown from American seed is attacked in preference to any other and that the cotton plant when grown upon black soil remains free from injury. The former fact could be accounted for by the American cotton being of a different species to that usually grown in India and probably offers seeds which are more suitable to development of the larvæ.

The reason for the greater susceptibility of and damage to the American cotton is undoubtedly that suggested by Mr. Saunders and is supported by many similar experiences with introduced plants or introduced plant pests. The hardy and rather unproductive cottons of India and other southern Asiatic countries probably long associated with this insect evidently were then and are still fairly resistant to its attacks, and, on the other hand, the introduced American and Egyptian varieties are

1 Saunders, W. W., Trans. Ent. Soc. London, Vol. III., pp. 284-85, 1843.

less resistant and perhaps furnish exceptional breeding conditions and were, therefore, when introduced into India and elsewhere in southern Asia, much more seriously attacked. This condition at once brought into prominence an insect which previously had been for the most part overlooked. It is significant that Dr. Barn should note that "native cotton is sometimes affected by it," indicating that it was a known but comparatively unimportant enemy of such cotton in India prior to 1842.

Saunders, in his article, makes no suggestion that the insect is other than a native Indian species, or, as has been stated by some writers, that it was imported with the American cotton. Responsibility for the theory of possible American at least African origin seems to rest with J. H. Durrant. This author, reviewing (1912)2 the specimens of Gelechia gossypiella in the British Museum, summarizes the earlier Indian records with an evident strong mental bias toward an inferred American or Egyptian origin. An examination of these records indicates that there is no real warrant for this bias. Of the Indian record of 1842, quoted above, from Saunders, he suggests the importation of the insect with American cotton simply because of the excessive damage to this introduced variety in comparison with native cottons, ignoring the perfectly reasonable explanation of this condition advanced by Saunders. The records for Cawnpore (1883) and Lahore (1893-94) report damage to "cotton " but this "cotton' is inferred by Durrant to be Egyptian because from other sources he learned that some Egyptian cotton was being experimentally grown at or near these places and, similarly, another record from Surat, about which no information was available, is assumed by Durrant to have a similar history.

August Busck (1917), following Durrant, without critical examination of the latter's data, accepts his general conclusions, and expresses the belief from this "evidence," and

2 Durrant, J. H., Bul. Ent. Research, Vol. III., Pt. 2, pp. 203-06, Fig. 1, London, 1912.

3 Busck, August, Jour. Agric. Research, U. S. D. A., Washington, Vol. IX., pp. 343-70, 6 pls., 1917.