in the three columns headed O-E (ObservedEinstein value that), relatively, the observed right-ascension deflections depart more markedly from the computed ones than do the observed declinations-deflections. The observed total deflections in every case, except for star 11, exceed the Einstein values.

nomical Expedition, at the Ile of Principe, west coast of Africa, where the weather conditions were unfortunately not as favorable as at Sobral, showed only a few stars and the scale could not be directly determined as it was not possible to remain at Principe the required time. Instead, plates of another region

Observer: A. C. D. Crommelin)

3 K2 Tauri 1.99 5.5 2 Pi. IV. 82 2.04 5.8 4 Ki Tauri 2.35 4.5 5 Pi. IV. 61 3.27 6.0 6 v Tauri 4.34 4.5 10 72 Tauri 5.19 5.5 11 56 Tauri 5.38 5.5

18. From the observational results in Table I., the resulting value of the deflection, a, at the sun's limb, as published by Dr. Crommelin, is 1".98,16 thus agreeing with the Einstein predicted value, 1".74, within 14 per cent. The result from the astrographic plates taken by the other British observer at Sobral, Mr. C. Davidson, using the astrographic object glass of the Greenwich Observatory in conjunction with a 16-inch colostat, was not so satisfactory, the star-images being diffuse on account of a probable change in figure of the colostat mirror; the discordance between the mean results from the individual plates was said to be rather large, but from the whole series an outward deflection reduced to the limb, of 0".93, or 0".99, according to the method of treatment, was found, with a probable error of about 0".3.16

19. The plates taken by Dr. A. S. Eddington and Mr. Cottingham, the second British Astro

16 See Nature, November 13, 1919, p. 281. The probable error as given by Dr. Crommelin is 0".12, whereas Dr. H. Spencer Jones, of the Greenwich Observatory, in his summary (Science Progress, January, 1920, p. 372) gives 0".06.

of the sky taken at the same altitude were used and compared with plates of the same region and of the eclipse-field obtained previously at Oxford. The determination of scale was therefore somewhat weak, though the uniformity of temperature at Principe was in its favor. The final result of the discussion of the plates gave an outward deflection of 1".61 with a probable error of 0".3.17

20. Except then for the unsatisfactory Sobral astrographic plates, the general conclusion to be drawn is that deflections of light were observed by the British astronomers that agree better with the Einstein law of gravitation (Cause b) than with the Newton-Maxwell law (Cause a). This is well shown by Fig. 2, constructed by the Department of Terrestrial Magnetism, giving a graphical representation of the law of variation with distance followed by the observed deflections for each star, as well as by the computed ones on the basis of causes a and b. It is seen at once that, excepting the most distant star (56 Tauri), each star shows a deflection agreeing better with the Einstein value than with the Newton-Maxwell

17 See reference to Dr. Jones's article in previous footnote.

more, that the preparations and securing of the requisite instrumental equipments were undertaken during the stress of the great war, every one will surely agree that the Astronomer Royal of England and the British observers are heartily to be congratulated upon the splendid results of their labors.

ANALYSIS OF OBSERVED LIGHT DEFLECTIONS

21. In conclusion an analysis was sketched of the observed light deflections and some evidences were pointed out showing that while the simple law (1) was followed to the greater extent, the effects in addition to varying inversely as the distance from the sun's center also apparently depended in some measure upon the heliographic latitude, 4, of the star. As a consequence the observed effects are not strictly radial, the departures from radiality occurring in a strikingly systematic manner, and not in the accidental manner that would be the case if the non-radial effects were attributable wholly to errors of observations. When such trigonometric functions are added to law (1) as would arise from forces similar in effect to centrifugal ones, the additional effects are largely accounted for. This possible additional cause, whatever it turns out to be, is designated as e. In complete allowance for differential atmospheric refraction effects in the earth's atmosphere may also be the cause of non-radial effects. Resolving the observed actual deflections into two components, radial (along radius vector) and the other non-radial (perpendicular to vector), preliminary computations were made with the aid of the expanded law.

the assistance received in the construction of diagrams and in the computational work from members of my staff, viz., W. J. Peters, H. B. Hedrick, C. R. Duwall and C. C. Ennis.

22. It is, of course, impossible without further analysis to state at present just what portion of the observed effects may be accounted for by the various causes described in paragraphs 14 and 21. Dr. Newall, for example, see reference in footnote 13, is ready to accept an effect from cause a (the NewtonMaxwell effect), but prefers considering the possibility of accounting for the greater portion of the remaining effect by cause c (Refraction in the Solar Atmosphere).

23. If it should prove to be the case that the observed light deflections are the result of a combination of the causes mentioned, the way may be open to explain the results obtained by Dr. W. W. Campbell's eclipse expedition of June 8, 1918, at Goldendale, Washington. Using two 4-inch photographic objectives photographs were taken of the sun and its surroundings, the exposures being 110 seconds, 50 stars to the ninth magnitude being recorded. He states his results as follows:19

The measurement of photographs, 14 inch X 17 inch in size, is a difficult problem even with suitable apparatus: we found it necessary to construct a special measuring machine, and this was made in our own shops. Duplicate photographs of the eclipse field were secured at Mount Hamilton seven months after the eclipse. As the difference of latitude between Mount Hamilton and the eclipse station is only a few degrees, no errors were introduced by not obtaining the comparison field at the eclipse station. These were taken at the proper altitude to avoid the chief refraction troubles in the comparison with the eclipse plates, so that second differences of differential refraction alone entered into the comparison. The plates were measured right and left. The same scale-divisions were used for corresponding pairs ruary 6, 1920, and slides were shown exhibiting the systematic character of these effects. The matter was gone into more fully at the New York meeting of the American Physical Society, February 28, 1920.

19 The Observatory, London, Vol. XLII., No. 542, August, 1919 (298-300).

of stars. As far as possible the measures were freed from any known source of error. The corrected differences of position were measured along radii from the sun to each star and were arranged in order of distance from sun to star. Dr. Curtis was not able to say that there was anything systematic about these differences, which showed no change of the order required by Einstein's second hypothesis. The probable error of one star posi tion was the order of 0".5, regrettably large when we are dealing with the differences of small quantities the difference between the expected displacements of the nearest and furthest stars only being 0".26. A telescope of great focal length would have been of great help in this work. For the one we used the stars were too faint and in the long exposure required we suffered from the increased extent of coronal structure. Curtis divided his stars into inner and outer groups. The differential displacement between the two groups should have been 0".08 or 0".15, according to which of Einstein's hypotheses was adopted. The mean of the results came out at 0.05 and of the right sign. After getting this result Curtis looked over the collection of 40-foot coronal plates. In the 1900 eclipse there were six stars fairly bright, but not well distributed. It is useless to take a duplicate photograph now owing to uncertainty in the values of the proper motions. Reference has been made to the Paris plate in the Carte du Ciel, but Curtis was unable to say from the comparison that the innermost star showed a displacement due to the Einstein effect.

"It is my own opinion," concludes Dr. Campbell, "that Dr. Curtis's results preclude the larger Einstein effect, but not the smaller amount expected according to the original Einstein hypothesis."

24. It will be observed that although Dr. Campbell was not so fortunate as the British astronomers in the matter of bright stars close to the sun, he obtained an effect at more than twice the distance from the sun of the farthest star (56 Tauri), shown in Fig. 2, in the right direction and of about the same amount as that given by cause a (Newton-Maxwell Effect). It is of interest to note here that the farthest star, 56 Tauri, in Fig. 2, also gave a deflection approaching that given by cause a, though since that star gave the largest probable error, not much weight is to be attached

to the fact. It would be of great importance to know, of course, whether as the distance of a star from the sun greatly increases, the deflections of light will correspond more and more closely with that given by cause a. There is no possibility that the Einstein effect with increased distance will merge into the Newton-Maxwell effect, since theoretically the former should always be twice the latter. However, if the main cause of light deflections should prove to be a, c and e, or a and e, or similar ones in effect, it may be possible, as already stated, to harmonize Dr. Campbell's results with those of the British observers. As a caution it may be well to bear in mind that Dr. Campbell unfortunately was obliged to get his results from very distant stars and hence had to look for quantities very much smaller than those concerned in the British observations of the solar eclipse of May 29, 1919.

OUTSTANDING MOTION OF MERCURY'S

25. As a further proof of the Einstein theory of gravitation has been cited the very satisfactory way20 in which the theory accounts for the outstanding motion of the perihelion of mercury, characterized by the late Professor Simon Newcomb as one of the greatest of astronomical puzzles. Dr. Charles L. Poor, of Columbia University, at the close of my lecture there on January 16 suggested that the outstanding motion of Mercury's perihelion could also be fully accounted for if the equatorial radius of the sun were found to exceed the polar radius by 0".5, so that the sun would not be truly spherical. Seeliger advanced the hypothesis21 "that the scattered zodiacal-light materials, if condensed into one body might have a mass fairly comparable to that of the little planet Mercury, "and he has concluded that the attractions of the zodiacal light materials upon the planet Mercury could explain the deviation of that planet from its

20 See A. S. Eddington's Report on The Rela tivity Theory of Gravitation, London, 1920, p. 52. 21 W. W. Campbell, "The Solar System," published in The Adolfo Stahl Lectures, p. 10, San Francisco, 1919.

computed orbit. This problem can not yet be regarded as definitely settled."

EINSTEIN DISPLACEMENT OF LINES OF SPECTRUM

26. Dr. Einstein appears to regard as essential to this theory the verification of the shifting towards the red of the lines of the spectrum of light from the sun and stars. However, Sir Joseph Larmor, according to a paper presented before the Royal Society on November 20, 1919, does not apparently agree with him. The predicted effect has not yet been successfully observed, or, as Professor Joseph S. Ames in his concluding remarks at the end of my lecture at the Johns Hopkins University put it, "has not yet been disentangled from the various possible other causes for shifts of the spectrum lines."

CONCLUDING REMARKS

27. The endeavor has been to set forth impartially all the facts pro and con with reference to the question of the verification of the Einstein theory of gravitation by the recent astronomical observations, so as to enable the reader to form an independent judgment and reach his own decision. Though we may differ as to whether the Einstein theory has been definitely verified, or not, one result of fundamental importance appears to have been established with fair certainty, upon which perhaps chief emphasis should be laid, viz.: that light has weight-just how much depends upon whether the Newtonian or the Einstein principles will ultimately be found correct. Possibly the best attitude to take is that of open-mindedness and to let no opportunity pass by for further experimental tests. The British astronomers are already zealously preparing to make observations during the solar eclipse of September, 1922, which will occur in Australia. Perhaps one of the most satisfactory results of the discussion aroused by the subject has been the stimulus imparted to further research in many fields, which is bound to bear fruit. LOUIS A. BAUER DEPARTMENT OF TERRESTRIAL MAGNETISM, CARNEGIE INSTITUTION OF WASHINGTON

UNITY AND BALANCE IN THE ZOOL

OGY COURSE

In an earlier number of this journal, apropos of an article by Professor Bradley M. Davis upon the botany course of the future, I briefly described the introductory course in zoology in operation for several years at the University of Michigan, and pointed out some of the advantages which a course centered around biological principles possessed over the usual course based on the dissection of types. Many inquiries concerning this course were received from all over this country, and several from the other side of the world, indicating a feeling of unrest and dissatisfaction with the present prevailing type course. Some of the writers of these letters clearly recognized the defects of the present method of teaching, and had striven to remedy them without completely reorganizing their courses. Others, while perceiving that something was wrong, had failed, it seems to me, to discern wherein lay the difficulties. In the hope that a clear understanding of the fundamental mistakes of the type course will assist in removing these difficulties, I have undertaken to present herewith what appear to me to be the requisites of the beginning course.

The nature of the first course in science should not be a matter of untrammeled opinion, it should be determined by certain principles. If those principles can be agreed upon, the details may perhaps be varied without harm. I submit two propositions which I regard as almost axiomatic, namely, that the course should be representative, and that it should possess unity. If these propositions are valid, the remainder of this article may have some value.

To apply the first of these rules, it is necessary to have in mind the content of the subject. On this question there may be differences of opinion, but most of these opinions can probably be arranged into two fairly well-defined groups. Zoology consists either (1) of a knowledge of Protozoa, Porifera, Coelenterata, Platyhelminthes, etc., or (2) of 1 SCIENCE, December 27, 1918.

a body of principles that may be brought under such rubrics as morphology, physiology, ecology, taxonomy, geographical distribution, paleontology, and evolution. Between these views the teacher must make a choice, if he is to make his course representative, and the nature of the course will depend upon his decision. If the first of these views of the content of zoology should prevail, he who studies cell permeability in Paramecium is to be regarded as a protozoologist, not as a physiologist, or else he is not a zoologist at all; the student of heredity in Drosophila is a dipterist, not a geneticist; and one who traces the origin of the horse is a mammalogist, not a paleontologist or evolutionist. Very few of the scholars mentioned would be content with the proposed appellation.

If the second conception of the content of zoology be entertained, as has been done in the preparation of our first course, the incongruities just referred to disappear. Other difficulties are also removed, for the seven divisions of zoology named above are not mutually exclusive, but overlap, a circumstance which, far from being a misfortune, is of much value in connection with the second proposition to be developed later. Genetics might fairly be added as an eight division, but its main features are either morphological, or physiological, or evolutionary.

The beginning course must contain the ele ments of each of these branches of the subject, if it is to be a general course. Whether the course should be general or not may be debated, but if it is to be general it must include something from each field.

The classical course in zoology is morphological, a dissection of types of the chief animal groups. Very little even of physiology has been included in it, until in recent years in a very few institutions. Such a course was the proper course once upon a time, when zoology was an almost purely morphological subject. But as the subject grew, the type course became a misfit. It has been a misfit for a long time.

Good teachers have attempted to ameliorate this growing inaptness of their courses by