. Journal of roentgenology . A THERMO-ELECTRIC CIRCUITThis Is a symbolic drawing. Thecircle as a whole represents thecomplete electrical circuit, the lefthalf being composed of a metalwhich emits electrons freely andthe right half of one which partswith Its electrons less easily. Ifthe junctions A and B are both atthe same temperature no currentwill flow, since the tendency to-wards a clockwise current whichexists at B Is exactly balanced bythe opposite tendency existing atA. However, when the junction AIs heated these tendencies are nolonger exactly in equilibrium andelectrons move around the
. Journal of roentgenology . A THERMO-ELECTRIC CIRCUITThis Is a symbolic drawing. Thecircle as a whole represents thecomplete electrical circuit, the lefthalf being composed of a metalwhich emits electrons freely andthe right half of one which partswith Its electrons less easily. Ifthe junctions A and B are both atthe same temperature no currentwill flow, since the tendency to-wards a clockwise current whichexists at B Is exactly balanced bythe opposite tendency existing atA. However, when the junction AIs heated these tendencies are nolonger exactly in equilibrium andelectrons move around the circuitin the direction of the arrows. It isnot necessary that the circuit shouldbe made up of equal masses of onlytwo different metals. It may bebroken at any point and long wiresof any sort of conducting substanceintroduced without altering its een-eral principle. Illustration Copied from ComstocTc and TrolandFigure One ORNDOFF —ROENTGEN TUBE. THE RELATIVE SIZES OF ATOMS AND MOLECULES This diagram Is Intended to give an Idea of the relative magnitudesof atoms and molecules. However, the drawings are only symbolic, asthe dimensions have been calculated on the assumption that the mole-cules are spherical, which cannot be strictly true. It will be noticed thatthe smallest atom (that of hydrogen) differs only slightly In size fromthe largest atom (that of uranium). The starch molecule is probablyone of the largest which exists and It will be seen that, according to thediagram, it is very much larger than the largest atom or than the mole-cule of sugar. The relative weights of the particles represented are as fol-lows: Hydrogen, 1; Uranium, 239; Sugar, 366; and Starch, not accu-rately known but probably about 25,000. A molecule of ordinary alcoholweighing 46, would be slightly larger than the uranium atom. Illustration Copied from Comstock and TrolandFigure Two THE JOURNAL OF ROENTGENOLOGYjournalofroentge1191west
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