"The Einstein theory in respect to the bending of a ray of star light as it passes near the gravitational field of the sun has been verified to the utmost satisfaction of all scientists by the recent measurement of the photographic plates taken by the Lick Observatory Expedition to Australia in the fall of 1922", said Professor H. T. Stetson in commenting on the recently published results of the solar eclipse expedition of 11922, sent under the auspices of the Lick Observatory to Wallal in northwester Australia, a point on the path of totality.
"When Einstein propounded his theory in 1905 he said that it must withstand three tests, the second of which concerned the recent expedition. It is that any star near the limb of the sun (edge of disc) should be displaced away from the sun's disc by 1.75 seconds of are on account of the influence of the magnetic or gravitational field of the sun on the star's light which must pass near the sun in order to reach the earth. According to Newtonian physics this displacement should amount to but 87 seconds of arc.
First Trials Unsuccessful
"The first important attempt to verify either of these predictions was made in May of 1919 by the Greenwich Observatory of England, when it made an expedition to Peru, a country in the path of totality. Although observations were made in three places, the results were not entirely satisfactory, largely because the plates did not agree very accurately. It is perfectly obvious that many photographs may be taken, some showing a displacement of from zero seconds of are to three seconds, the average being the predicted displacement of 1.75 seconds of are;--but this proves nothing other than poor photography.
Climate Affected Photographs
"These inaccurate prates were caused by several things. The climate, being warm, made it necessary to develop the plates in warm solutions, which often resulted in flukes or distortions in the photographs. Then again, since the cameras were not pointed directly at the starts, but received the solar and star rays by means of mirrors reflecting, the light into the lenses, the images of the stars were subjected to distortions even before they reached the camera lens, because the mirrors expanded or contracted with the slightest change in temperature. A third criticism arose over the method of measuring these plates used by the Greenwich Observatory. to the ordinary individual it would seem a trivial matter whether the sensitive side of the plate on which was the actual photograph was measured or whether the sensitive side was studied from the clear side of the plate, thus necessitating looking through the glass of the plate. The method of measurement necessitated looking through the glass and because of the minute refraction due to light passing through an eighth or quarter of an inch of glass, the accuracy of the results have been doubted.
Expedition was Carefully Planned
"Profiting by the mistakes of this expedition the Lick Observatory in California prepared for many months its expedition. W. W. Campbell was made director. The first action was that of photographing that region of the sky in which the sun would be three months later.
"Two specially constructed cameras were made,--the diameter of the lens being five inches and the focal length 15 feet. These cameras had refracting lenses and were pointed directly at the point in the sky where the eclipse would occur. This avoided any distortions due to expanding and contracting mirrors. The photographic plates were of plate glass and were 17 inches square. The temperate climate of Australia further facilitated matters.
"After the actual photography work had been done on September 21, the day of the eclipse, the plates were returned to California and measured with an unquestionable precision. Five-sixths of the plates have been measured at the present time, and inasmuch as no great difference of displacement is expected in the remainder of the plates, the Lick Observatory will not again verify the theory at the total solar eclipse which sweeps Mexico and Lower California next fall.
"The average of the results obtained showed a displacement of 1.74 of are which compares favorably with the Einstein prediction of 1.75 seconds of arc and overrides the Newtonian calculations of 87 seconds. But as I have mentioned before the average proves nothing. The real merit of the result lies in the small variation in so many plates. The minimum displacement was 1.58 seconds of arc and the maximum 1.86 seconds. The results were derived from the measurement of 60-80 star displacements on each of four plates. The accuracy of the photography could not be denied, after the consistency of the results is considered.
"Two parts of the Einstein theory have been verified. The first of these merely accounts for the peculiarity in the precession of the orbit of Mercury. The precession of this orbit does not seem to obey the Newtonian law of gravitation, inasmuch as the precession exceeds by 42 seconds of are a century any possible precession under the Newtonian laws. Einstein's theory accounts for this difference most satisfactorily.
"The second test satisfactorily accounted for it the bending of the ray of light.
Believes Theory Will Be Accepted
"At present," concluded Professor Stetson, "the theory satisfactorily accounts for the irregular processional motion of the orbit of Mercury, and for the displacement of starlight passing through the sun's magnetic field on its way to the earth. If the Einstein theory of relativity is conclusively established, as no doubt it will be, the change in human thinking caused will be as great as that upheaval caused by Copernicus in substituting the heliocentric for the geocentric system of planetary motion, or, in other words, in maintaining that the sun and not the earth is the center of the solar system. As soon as the theory is generally understood, there will hardly be a single phase in human life unaffected, and man's conception of the universe must be materially revised in order to include the new truth, that space and time cannot exist without cosmic matter.