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PHILADELPHIA, 104 South FIFTH STREET,

APRIL 5, 1897. THE AMERICAN PHILOSOPHICAL SOCIETY held at

1 Philadelphia for Promoting Useful Knowledge has the honor to announce that an award of the Henry M. Phillips Prize will be made during the year 1899; essays for the same to be in the possession of the Society before the first day of May, 1899. The subject upon which essays are to be furnished by competitors is :

The development of the law, as illustrated by the

decisions relating to the police power of the State. The essay shall not contain more than one hundred thousand words, excluding notes. Such notes, if any, should be kept separate as an Appendix.

The Prize for the crowned essay will be two thousand dollars lawful gold coin of the United States, to be paid as soon as may be after the award. The Society invites attention to the regulations governing said prize, which accompany this circular.

William V. McKean, Craig Biddle, Mayer Sulzberger,
C. Stuart Patterson, Joseph C. Fraley, Frederick Fraley,
President of the Society, Horace Jayne, M.D.,* Treasurer
of the Society, Committee on the Henry M. Phillips Prize

Essay Fund.
The essays must be sent, addressed to Frederick Fraley,
President of the American Philosophical Society, Philadelphia.

* Elected Treasurer American Philosophical Society, January 7, 1898, in place of J. Sergeant Price, Esq., deceased, August 16, 1897.

REGULATIONS. Competitors for the prize shall affix to their essays some motto or name (not the proper name of the author, however), and when the essay is forwarded to the Society it shall be accompanied by a sealed envelope, containing within, the proper name of the author, and, on the outside thereof, the motto or name adopted for the essay.

At a stated meeting of the Society, in pursuance of the advertisement, all essays received up to that time shall be referred to a Committee of Judges, to consist of five persons, who shall be selected by the Society from nomination of ten persons made by the Standing Committee on the lenry M. Phillips Prize Essay Fund.

Essays may be written in English, French, German, Dutch, Italian, Spanish or Latin; but, if in any language except English, must be accompanied by an English translation of the same,

No treatise or essay shall be entitled to compete for the prize that has been already published or printed, or for which the author has received already any prize, profit, or honor, of any nature whatsoever.

All essays must be clearly and legibly written or printed on one side of the paper only.

The literary property of such essays shall be in their authors, subject to the right of the Society to publish the crowned essly in its Transactions or Proceedings.

PROCEEDINGS

OF THE

AMERICAN PHILOSOPHTOAL SOCIETY,

HELD AT PHILADELPHIA, POR NOMOTIBDSETEUS KNOWLEDGE. Vol. XXXVII. Januar__1898. JE, No. 157.

Stated Meeting, January 7, 1898.
Dr. J. C. MORRIS in the Chair.

Present, 17 members. Dr. T. J. J. See and Mr. Sydney Geo. Fisher, newly elected members, were presented to the Chair and took their seats.

Acknowledgments of election to membership were read from Messrs. Charles De Garmo, Arnold E. Ortmann, Thomas J. J. See, Alden Sampson, Sydney George Fisher, Benjamin Kendall Emerson, Francis L. Patton, Edward S. Holden, and Ethelbert Dudley Warfield.

An invitation was received from the Academy of Natural Sciences of Philadelphia, to participate in a memorial meeting commemorative of Harrison Allen, M.D., and George H. Horn, M.D., to be held at the Academy on December 31, at 8 o'clock.

The Judges and Tellers of the annual election reported the following officers elected for the ensuing year :

President.
Frederick Fraley.

Vice-Presidents.
E. Otis Kendall, William Pepper, Coleman Sellers.

Secretaries.
Persifor Frazer, I. Minis Hays, Frederick Prime,

S. P. Sadtler.

Curators. J. Cheston Morris, Benjamin Smith Lyman, Henry Pettit.

Treasurer.

Horace Jayne.

Councillors for three years.
Henry C. Baird, Isaac J. Wistar, Jacob M. DaCosta.
Councillor for one year, to fill an unexpired term.

George F. Edmunds. Dr. I. Minis Hays was nominated for Librarian for the ensuing year.

Prof. Cleveland Abbe read a paper on “ The Accepted Altitude of the Aurora Borealis."

Mr. Sachse and Mr. Cook offered some remarks in discussion.

Dr. T. J. J. See presented a paper for the Transactions on “ The Evolution of the Stellar Systems,” which was discussed by Prof. Doolittle, Prof. Snyder, Dr. See and Prof. Abbe.

The Society was adjourned by the presiding member.

THE ALTITUDE OF THE AURORA ABOVE THE

EARTH'S SURFACE.

BY CLEVELAND ABBE.

(Read January 7, 1898.) During the past three centuries numerous observers and physicists, astronomers and magneticians have endeavored to contribute to our knowledge of the altitude of the region whence the auroral light proceeds, and still the greatest diversity of opinion seems to prevail on this subject. Some observers have seen the light in such positions between themselves and neighboring objects as to demonstrate that the aurora, like the lightning, descends to the very surface of the earth and may even be entirely confined to the lowest stratum : prominent among these are Captain Parry, Sir James Clark Ross and Sir John Ross, his uncle, Dr. Walker and Prof. J. P. Lesley.

Others, such as Dr. Richardson, Sir John Franklin, Silbermann, have seen it so located among the clouds that its origin must be placed at or below their level and, therefore, within a few thousand feet of the earth's surface. On the other hand, those who have calculated the altitudes of specific beams and arches by trigonometrical or equivalent methods have generally found figures indicating altitudes between twenty and a hundred miles. Perhaps the highest altitudes that have been deduced were the following: Dalton, 150 miles; Loomis, 400 to 600; Bergman, 468; Boscovich, 825 ; Fournerius, 1006; Twining, 1100 ; Boller, 2000 kilometers, or 1 243 miles.

Those who delight in numerical calculations accept these larger altitudes and content themselves with saying that the altitude of the aurora ranges from 50 miles upward to 1000. The experimental physicists, by studying the analogies between the auroral light and the discharge of electricity through vacuum tubes, have shown that the auroral phenomena harmonize in part at least with those observed in vacua such as might occur at moderate altitudes. Thus, Miller and De La Rue give altitudes of from ten to forty miles. Espy and Bache maintained that observers a few miles apart did not and could not have observed the same arches. The most careful observers have in many cases defended the accuracy of the observations made under circumstances that admit of no doubt that the auroral light in the free atmosphere often emanates from points within a few yards of the observer.

Lemstrom has sought to reconcile the diverse conclusions by maintaining that while many auroras are quite high up and belong to the upper air, yet those in extreme northern latitudes most generally belong to the lowest strata and follow the unevenness of the ground, appearing as glows around the mountain top, or as rays directed toward prominent objects.

The object of the present paper is to study some of the numerous observations, calculations and opinions bearing on the nature and the altitude of the auroral light. We shall not especially consider the electrical origin, or the source of the electricity, but simply acquiesce in the universal conviction that it really is one form of electrical discharge, our main object being to ascertain whether we can in any way definitely fix its locus in the atmosphere.

The most instructive method of procedure consists in taking up the consideration of a number of authorities in chronological order, by which means one is led to appreciate the slow progress of knowledge and the difficulty which many investigators have felt, from time to time, in giving up preconceived views without having anything better to accept in their place. There is nothing more difficult than to recognize the fact that all our ideas are wrong, and that we are wholly in the dark with regard to the nature of that which our eyes behold so plainly. How many thousands of years elapsed before modern science gave us any clue to the true nature of the rainbow, and how difficult it has been to eradicate from our textbooks the crude ideas of Descartes, Huyghens and Sir Isaac Newton which made the rainbow to be a phenomenon of dispersion and substitute the correct view of Thomas Young, who showed it to be a phenomenon of interference.

Possibly we must go through a similar series of changes in our views with regard to the auroral light until we recognize that each observer sees his own aurora as a so-called optical illusion.

There are several forms of optical illusion that are evidently connected with the aurora. Some of these were recognized long since, while others are still deceiving our senses and perplexing our calculations.

As we pursue our reading chronologically, among the different authorities, we shall perceive how one after another is led to suspect and fully recognize some one or other of these optical or perspective illusions, while others, inattentive thereto, plunge deeper into misleading calculations. If, at the end of our consideration of the subject, we sum up all that has been shown to be probable or demonstrated to be true, we shall almost necessarily conclude that the determination of the altitude of the aurora is a much more delicate problem and perhaps also a more indefinite problem than we have hitherto believed.

After reviewing the literature of the subject since the time of Halley, we find that the methods of determining the altitude of specific features of the aurora may be enumerated as follows: (1) Parallax method ; (2) Galle's first method; (3) Galle's second method; (4) Bravais method of amplitudes and its modifications by Fearnley, Newton, Nordenskiold and Bergmann ; (5) Bravais' method by the apparent breadth of the arch ; (6) Bravais' velocity method ; (7) my method, by the simultaneous motion of waves at the zenith and beams above an arch; (8) Gyllenskiold's method, by the apparent length of the auroral beam.

All these agree in one fundamental assumption, that the observed beams and arches have an individual existence and a definite locus. But this assumption is negatived by the equal frequency of negative and positive parallaxes whenever the parallax method is applied.

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