" general storm " phenomena by the magnetic latitude. He discusses the electrical current systems supposed to " flow in more or less horizontal strata in the upper atmosphere " to which the magnetic changes he has arrived at may be ultimately ascribed. The external currents will, of course, be accompanied by corresponding induced currents within the earth which will modify their effects." Taking what he considered an average storm, Chapman calculated that it called for the expenditure of energy at the rate of about 2XIO 18 ergs per second for 15 hours.
To many minds theoretical researches of this kind are fascinating, but deductions from them, until confirmed by direct observation, are just as hypothetical as the theories themselves.
A statement of the respects in which there is a lack of uniformity or symmetry in magnetic phenomena may thus be of service in more ways than one. The complete Gaussian analysis indicates in reality a considerable departure from symmetry round an axis. High latitudes, moreover, were practically unrepresented in the data used for calculating the Gaussian constants, while the asymmetry in the positions of the north and south magnetic poles suggests that the result of the analysis may depart most from reality in the very regions where aurora and magnetic storms are most developed. Whatever may be true of a hypothetical aurora or magnetic storm representing the mean of a large number, the individual aurora or magnetic storm shows no approach to symmetry round a magnetic axis. The magnetic disturbance, though universally experienced, seems on a given occasion developed to a very different extent at stations having the same magnetic latitude. Even when there is a recognizable S.C. the sequence of events is widely different at different places, and on different occasions varies much at any one station. In low latitudes the S.C. is a change mainly in H, almost invariably a rise. This enhancement usually persists for a short time, and is then followed by a fall, which brings H below its normal value. But even in low latitudes an oscillation may often be seen in one or more of the elements; while in higher latitudes the S.C. movement is usually oscillatory in all the elements, the first and smaller change in H being a fall. The duration of the enhanced value in H following the S.C. is very variable. Sometimes it lasts five or six hours; sometimes, especially in large storms, a reversal and large drop occur within a minute or two. The superposition, following " storm time," of disturbance curves, unless these be sorted out, may lead to no happier results than the superposition of measurements taken from animals varying promiscuously from a giraffe to a whale. The result may be to give us a storm such as never existed. The average intensity even of magnetic disturbance must depend on other things than the magnetic latitude as defined by Chapman. According to this defini- tion Agincourt (Toronto) and Kew are very similarly situated, but during 1911-2 disturbance was almost invariably much larger at Agincourt than at Kew. Again, the relative amplitude of magnetic oscillations at stations so comparatively near together as Kew, Stonyhurst and Eskdalemuir depends on the season of the year, and is considerably different in different years. Chapman's estimate of the energy of a magnetic storm depends fundamentally on several assumptions, the degree of probability of which is at present entirely a matter of opinion. But the estimate is at all events enormously less improbable than that made in 1892 by Lord Kelvin, on the hypothe- sis of direct magnetic action between the sun and the earth. Kelvin's numerical figure is nearly the square of Chapman's. Before another nears have elapsed magnetic phenomena may have been sufficiently investigated to admit of a really satisfactory comparison of theory and observation, but at present that stage has not been reached.
REFERENCES. The journal Terrestrial Magnetism and Atmos- pheric Electricity contains original papers and many references. See also the following: Researches, vols. i., ii. and iii. (Carnegie Institu- tion of Washington, Dept. of Terrestrial Magnetism) ; C. Chree, Studies in Terrestrial Magnetism (1912); Daniel L. Hazard, Direc- tions for Magnetic Measurements (1911); E. Merlin and O. Simyille, Lisle des Observatoires Magnetiques et des Observatoires Seismologiques (1910); A. ' Nipppldt, "Erdmagnetismus," in Muller-Pouillet's Lehrbuch der Physik und Meteorologie, 4ter Band, stes Buch (1914); A. Schmidt, " Erdmagnetismus," in Encyklopddie d. Math. Wiss., 6ter Band (1917); The Scientific Papers of the Hon. Henry Cavendish, vol. ii., Magnetic Work (1921). For surveys of different countries and results of survey expeditions: A. Angot, Reseau Magnctique de la France et de I'Afrique du Nord au I" Janvier ion (1911); C. Cole- ridge Farr, Magnetic Survey of the Dominion of New Zealand and some of the outlying islands for the epoch joth June 1903 (1916); A. Hermant, Leve Magnetique de la Belgique au i" Janvier 1913 (1920); A Magnetic Survey of Japan for the epoch 1913 executed by the Hydrographic Office, Bulletin of the Hydrographic Office, Imperial Japanese Navy, vol. ii. (1918); G. W. Walker, The Magnetic Resurvey of the British Isles for the epoch Jan. I 1915, Roy. Soc. Phil. Trans. A, vol. ccxix. (1919). For expeditions see: Fr. Bidlingmaier, Kurvensammlung von Erdmagnetischen Variationen beo- bachtet 1902-03 auf der Gauss-Station im Sudlichen Eismeer (1912); Kr. Birkeland, The Norwegian Aurora Polaris Expedition 1002-1003 (first section 1908, second section 1913); British (Terra Nova) Antarctic Expedition 1910-1913, Terrestrial Magnetism (1921); Kurt Molin, Wissenschaftliche Ergebnisse der Schwedischen Siidpolar- expedition 1901-1903, unter Leitung von Dr. Otto Nordenskjold: Erdmagnetische Ergebnisse (1920). (C. CH.)
MAHAFFY, SIR JOHN PENTLAND (1830-1919), Irish classical scholar (see 17.394). He became vice-provost of Trinity College,
Dublin, in 1913 and succeeded Dr. Traill as provost in 1914. His
provostship covered an eventful period in the history of Ireland
and of the college, and Dr. Mahaffy took an active part in the
questions which agitated the country. He was a vigorous supporter
of the cause of the Allies in the World War, and encouraged the
loyal effort of the college, which sent practically all its young men
who were eligible for service to the front. Though a strong
Unionist by conviction, he believed that the conditions after the
rebellion of 1916 necessitated compromise. At his invitation the
Irish Convention met in Trinity College in 1917, and Dr. Mahaf-
fy, who was one of the members nominated by the Government,
took an active part in the debates. He pressed for a solution of
the Irish question on the lines of Swiss federalism, and embodied
his views in a minority report which was signed also by Dr.
Crozier, Protestant Archbishop of Armagh. In recognition of the
services of the college during the war, Dr. Mahaffy was in 1918
made a G.B.E., the Lord Lieutenant, Visct. French, at the same
time giving him the accolade. Dr. Mahaffy was thus the first
Roman Catholic priest to be made a knight. Dr. Mahaffy held
many foreign and other distinctions; he was a D.C.L. of Ox-
ford, an LL.D. of St. Andrew's, a Ph.D. of Louvain and a Ph.D.
of Athens, as well as a corresponding member of several for-
eign learned societies. From 1911 to 1916 he was president of
the Royal Irish Academy. He died April 30 1919.
MAHAN, ALFRED THAYER (1840-1914), American naval officer and historian (see 17.394), died in Washington, D.C., Dec. 1 1914. His later works included The Interest of America in International Conditions (1910); Naval Strategy Compared and Contrasted with the Principles of Military Operations on Land (1911, lectures delivered at the U.S. Naval War College, Newport, R.I., between 1887 and 1911); Armaments and Arbitration (1912) and The Major Operations of the Navies in the War of American Independence (1913).
See C. Carlisle Taylor, The Life of Admiral Mahan (1921).
MAHOMMED V. (1844-1918), Sultan of Turkey, was born at Topkapu Nov. 3 1844, a younger son of the Sultan 'Abdul Mejid (1822-1861). He led a quiet and retired life, and suffered at times considerably from the jealousy and suspicion of his elder brother, the Sultan 'Abdul Hamid II. On the deposition of 'Abdul Hamid he was invested as caliph (April 27 1909). He was for the most part merely a tool in the hands of the Committee of Union and Progress, and though he was supposed to dislike the pro-German policy of Enver Pasha, he was unable to take any effective steps to oppose him. He died at Yildiz July 3 1918, and was succeeded by his brother Vahid-ed-Din (b. 1861), who took the title of Mahommed VI.
MAINE (see 17.434). The pop. of the state in 1920 was 768,014, in 1910 742,371, an increase of only 3-5%, as compared with 14-9% for the United States in the same period and 6-9% for Maine in the previous decade. There was a significant in- crease in urban population. The proportion living in places of 2,500 or more was 33-5% in 1900, 35-3% in 1910 and 39% in 1920. In 1910 the rural pop. was 480,123; in 1920, 468,445. The only one of the 16 counties showing a marked increase in rural pop. was Aroostook, which is one of the richest farming regions of New England.
The principal cities of the state, with their pop. of 1920 and rate of increase, were as follows:
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City
1920
1910
Increase percent.
Portland Lewiston Bangor Biddeford Auburn Bath
69,272 3i,79i 25,978 18,008 16,985 i4,73i 14,114
i3,35i
58,571 26,247 24,803
17,079 15,064 9,396 13,211 11458
18-3
2I-I
4'7 5-4
12-8
56-8 6-8 16-5
Augusta Waterville
Of these cities Bath showed the largest increase, 56-8%, due to the shipbuilding activity in the World War period.
