strikes an atom, from a potential V, and causes radiation of a frequency v, such that

The frequency emitted in the direction in which the electron is going ought then to be

(I

n)e V

ข

In cases where ʼn is nearly zero this may be written approximately

η

is of the dimensions of a potential, and equal to 253.7

=

So if V 63 kv., for example, this derivative becomes

This is zero for n = 1/16 at which point the frequency emitted be

eV

This is so far above the observed limit as to be definitely

contrary to experimental facts. 73

h

But with the effects observed, especially in Wagner's experiments, what hypothesis can we adopt? The facts seem to point to a Doppler effect at the lower frequencies, and there seems to be no other explanation of them on hand now. Is it possible that we are wrong in saying that all the energy of the cathode electron not going to radiation must remain as residual kinetic energy of

this electron alone? May not the particle it strikes get some of the energy? Or is there after all some totally different explanation of these effects? One point alone is certain: we need more facts.

1 J. Trowbridge, Amer. Acad. Proc., 33, 1898 (435-451); Amer. Journ. Sci., 9, June 1900 (439-441).

2 R. Whiddington, Roy. Soc. Proc., Ser. A, 85, July 1911.

3 R. T. Beatty, Roy. Soc. Proc., Ser. A, 87, Dec. 1912.

4 See W. H. and W. L. Bragg, "X-Rays and Crystal Structure," p. 73.

5 W. Duane and F. L. Hunt, Phys. Rev., 6, Aug. 1915 (166–171).

6 D. L. Webster, Nat. Acad. Proc., 2, March 1916 (90-94); Phys. Rev., 7, June 1916 (599-613).

7 D. L. Webster and H. Clark, Nat. Acad. Proc., 3, March 1917 (181-185).

8 D. L. Webster, Phys. Rev., 6, July 1915 (56).

9 D. L. Webster, Phys. Rev., 9, Mar. 1917 (220-225).

10 B. Davis, Phys. Rev., 9, Jan. 1917 (64-77).

11 A. W. Hull, Phys. Rev., 7, Jan. 1916 (156).

12 Ledoux-Lebard and A. Dauvillier, C. R., 163, Dec. 1916 (754); Ibid., 164, Apr. 1917 (687).

13 Dessauer and Bach, Ber. d. D. Phys. Ges., 21, 1919 (168).

1 C. T. Ulrey, Phys. Rev., 11, May 1918 (401-410).

15 A. Müller, Phys. Zeit., 19, 1918 (489).

16 E. Wagner, Ann. der Phys., 57, Dec. 1918 (401–470).

17 F. C. Blake and W. Duane, Phys. Rev., 10, Dec. 1917 (624-638).

18 E. Rutherford, J. Barnes and H. Richardson, Phil. Mag., 30, 1915 (339).

19 F. Dessauer, B. d. D. Phys. Ges., 19, 1917 (155).

20 E. Wagner, Jahrb. d. Radioak u. Elek., 16, 1919 (190).

21 R. Ledoux-Lebard and A. Dauvillier, C. R., 169, Nov. 24, 1919 (965-967).

22 A. W. Hull and M. Rice, Nat. Acad. Proc., 2, May 1916 (265-270).

23 B. A. Wooten, Phys. Rev., 13, Jan. 1919 (71–86).

24 D. L. Webster, Nat. Acad. Proc., 6, Jan. 1920 (26-35).

25 F. C. Hoyt, Nat. Acad. Proc., 7, 1920.

26 See Sommerfeld, "Atombau und Spektrallinien."

2: W. Duane, Bulletin of the National Research Council, 1, 1920.

28 D. L. Webster, Phys. Rev., 16, July 1920 (31-40).

29 W. Kossel, Zeit. für Phys., 1, 1920 (119).

30 W. Stenstrom, Ann. der Phys., 59, 1919 (56); or Diss., Lund, 1919.

31 H. Fricke, Phys. Rev., 16, 1920 (202).

32 W. Duane and R. A. Patterson, Nat. Acad. Proc., 7, 1920.

33 W. Kossel, V. d. D. P. G., 16, Nov. 1914 (898 and 953).

34 W. Duane and T. Shimizu, Phys. Rev., 14, July 1919 (67–73).

35 W. Duane and W. Strenström, Phys. Rev., 15, April 1920 (328-330).

36 W. Duane and R. A. Patterson, Phys. Rev., 15, April 1920 (328).

37 Benoist, J. de Phys., 1901 (653-668).

38 C. D. Miller, Phys. Rev., 8, Oct. 1916 (325-343).

ვე J. E. Lilienfeld, Phys. Zeit., 19, June 1918 (263-269).

40 J. E. Lilienfeld, Ber. d. Sächs. Ges. d. W., 69, 1917 (226).

41 H. Behnken, Zeit für Phys., 3, 1920 (48-59).

42 A Dauvillier, Thesis Universite de Paris, 1920.

43 R. T. Beatty, P. R. S., A, 87, 511; 89, 314.

44 See D. L. Webster, Nat. Acad. Proc., 5, May 1919 (163-166).

45 A. Sommerfeld, Ann. der Phys., 46, March 1915 (721-748).

46 D. L. Webster, Phys. Rev., 6, July 1915 (56).

47 W. Duane, Science, Oct. 12, 1917 (347).

48 B. Davis, Phys. Rev., 9, Jan. 1917 (64-77).

49 H. Brillouin, Comptes rendus, 170, Feb. 2, 1920 (274–276).

50 D. L. Webster. Phys. Rev., 9, Mar. 1917 (220–225); Nat. Acad. Proc., 5, May 1919 (163-166).

51 Berliner Ber., 1897 (395).

52 Walter, Fortschr. a. d. Geb. d. Röntgenstr., 11, 1907.

53 E. Bassler, Ann. der Phys., 28, 1909 (808).

54 C. G. Barkla, Nature, Mar. 17, 1904, and Mar. 9, 1905; Phil. Trans. Roy. Soc., A, 204, Feb. 1905 (467–479).

55 J. C. Chapman, Phil. Mag., 25, 1913 (792).

56 C. G. Barkla, Roy. Soc. Proc., A, 77, Feb. 1906 (247-255).

57 H. Haga, Ann. der Phys., 23, July 1907 (439-444).

58

J. Herweg, Ibid., 29, May 1909 (398–400).

59 L. Vegard, Roy. Soc. Proc., 1910.

60 G. W. C. Kaye, Proc. Camb. Phil. Soc., 15, 1909 (269-272).

61 J. Stark, Phys. Zeitschr., 10, Nov. 22, 1909 (902-913).

62 A. Sommerfeld, Phys. Zeitschr., 10, Dec. 15, 1909 (969-976). 63 W. W. Loebe, Ann. der Phys., 44, 1914 (1033-1052).

64 W. R. Ham, Phys. Rev., 30, Jan. 1910 (96–121).

65 F. C. Miller, Franklin Inst. Jr., 171, May 1911 (457-461).

66 W. Friedrich, Ann. der Phys., 39, Sept. 24, 1912 (377-430).

67 H. Kirschbaum, Ann. der Phys., 46, 1915 (85-129).

68 E. Wagner, Report on the Continuous X-Ray Spectrum, J. d. Rad. Elek., 16, Dec. 1919 (212).

69 D. L. Webster, Phys. Rev., 13, Apr. 1919 (303–305).

70 A. L. Parson, Smithsonian Miscellaneous Collections, 65, Nov. 1, 1915.

71 Loc. cit., note 6, and Amer. Acad. Proc., 50, Jan. 1915 (131–145).

72 A. H. Compton, Phys. Rev., 14, June 1919 (20-43); Ibid., 14, Sept. 1919 (247–259). 73 Since this was written a paper has arrived, describing some experiments by G. Zecher (Ann. der Phys., 63, 1920 (28-55)), that seem to show an effect of just the sort indicated by this calculation. He used molybdenum at 80 kilovolts and found a Doppler effect of 11 per cent where the above theory would indicate about 8 per cent.

The evidence, however, is far from satisfactory, for Zecher used an induction coil and a set of gas-filled valve tubes. This made the potential very unsteady and the high frequency limit correspondingly indefinite-so indefinite, in fact, that it depended to a considerable extent on the time of exposure of his plates. And some of his other measurements indicated a difference in the high frequency limits at 90° from molybdenum and tungsten tubes running in parallel, which is contrary to the more reliable measurements made with direct currents by other observers, especially Hull and Rice, and Ulrey. But Zecher, himself, says this latter effect may be due to a difference in the tubes, rather than in the targets. In view of all these facts we have good ground for the belief that the observed difference in the high frequency limits in different directions may be due to absorption effects, and not to the Doppler effect that Zecher ascribes it to.

Even if this is a true Doppler effect, we certainly can not accept Zecher's explanation of it, as a confirmation of Sommerfeld's theory of 1909, which was based on the pulse theory. For, as noted above, this theory gives no explanation of the high frequency limit at all, and so it surely can not give a satisfactory explanation of any shift of such a limit. If the effect is real, it is more likely to be due to the causes discussed above.

INTELLECTUAL AND EDUCATIONAL STATUS OF THE MEDICAL PROFESSION AS REPRESENTED IN THE UNITED STATES ARMY

BY MARGARET V. COBB AND ROBERT M. YERKES

Classification of the medical schools by entrance requirements.

Classification according to rating of American Medical Association.

Classification by medical sect..

517

522

525

Comparison of schools..

529