Weight Tossing

If young Dr. Kenneth T. Bainbridge stood in the gallery of a theatre and threw handfuls of lemons, oranges and grapefruit at the stage, he would no doubt be ejected by the police. But if there existed no scales on which to weigh lemons, oranges and grapefruit, the police would doubtless let him throw to his heart's content. Thrown with equal force, the lemons would hit players, the oranges would land in the orchestra pit, the grapefruit on the heads of $5.50 seat-holders. Then Dr. Bainbridge could measure the distance between a grapefruit-splashed spectator and an orange-struck piccolo player, between piccolo player and comedian, and presto, he would know the relative weights of lemons, oranges, grapefruit.

The actual throwing that Dr. Bainbridge did last week was carried on in a much smaller theatre, with much smaller projectiles. His theatre was a huge mass-spectrograph; his projectiles, atoms. What earned him scientific plaudits rather than police treatment was the fact that his instrument was bigger than anything that had previously been developed in the U. S., could therefore compute relative weights which differed by less than one-trillionth of one-trillionth of an ounce.

Most elements have two or more isotopes; i. e., appear in different forms, which, though outwardly similar, have different atomic construction, different weights. Though the average atomic weights of all the elements are known, the precise weights of the different isotopes of many elements are not known. Dr. Bainbridge expects his spectrograph to remedy that.

He put some neon into one end of a vacuum chamber. Neon, having three isotopes, is comparable to a lot of lemons, oranges and grapefruit in a paper bag.' Dr. Bainbridge knew the weight of the whole, also the average weight of each piece of his "fruit," but (he assumed) not the weight of each individual piece. So he propelled the neon atoms through the chamber with an electric force, strong enough to blow the "bag" to pieces, ionize the atoms. Two huge electromagnets created a powerful magnetic field, which, like gravity pulling the fruit to earth, defleeted the course of the ionized atoms. Dr. Bainbridge snapped a picture. The lightest isotopes, like lemons, had traveled farthest, the medium isotopes not so far, the heavy "grapefruit" isotopes, a still shorter distance. By measuring the distances between them on the plate Dr. Bainbridge could calculate the relative weights of Ne20, Ne21, and Ne22. He thinks he can do the same for many another isotope of many another element, including the isotope of hydrogen, found last December (TIME, Dec. 21). By weighing the hydrogen isotope he thinks he may be able to throw some light on what happens to .0308 of hydrogen's atomic weight (1.0077) when four atoms of it combine to form one atom of helium (atomic weight: 4). It is that lost energy which Dr. Robert Andrews Millikan thinks is converted into cosmic rays which splatter about the earth and seep into teacups.

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