May 19, 1892] 



NA TURE 



67 



MAGNETIC VARIATIONS} 

 T N this paper the author refers to the ordinary variations of the 

 -'■ magnetic elements as observed at Greenwich ; the annual 

 progressive change ; the diurnal variation — large in summer, 

 small in winter, and also larger when sun-spots are numerous 

 and smaller when sun-spots are few ; the irregular magnetic dis- 

 turbances and magnetic storms, and the accompanying earth 

 currents ; phenomena which are generally similar at other places. 



He then invites attention more particularly to magnetic dis- 

 turbances. Those at Greenwich may, after a calm period, arise 

 gradually or commence with great suddenness. When sudden, 

 the movement is simultaneous in all elements. The first indica- 

 tion may be a sharp, premonitory, simultaneous movement, 

 followed after a time by general disturbance, or the movement 

 may at once usher in the disturbance. These initial movements 

 are not always great in magnitude, sometimes, indeed, small, but 

 they have a very definite character, and frequently occur nearly 

 instantaneously, as is shown in the character of the photographic 

 traces. 



It has been long known that magnetic disturbances occur at 

 the same time over wide areas of the earth's surface, but the 

 accidental comparison in past years of the times of commence- 

 ment of one or two disturbances at Greenwich with the times at 

 other places has led the author to suppose that the coincidence 

 in time is much closer than had been before supposed, and the 

 definite, and on occasions isolated, character of the initial 

 movement induced him to undertake the collection and 

 comparison of the times of such movements for a number of days 

 at observatories geographically widely separated. 



The times of such movements cannot be caught by eye 

 observation without continuous watching of the magnets, so that 

 the photographic regi>ters have to be relied upon, which is 

 better, excepting that the scale of time is necessarily contracted; 

 but, though in individual measures there might be variations, 

 it was conceived that (supposing no systematic error to exist) 

 the mean of a number of comparisons should give a good result. 

 Seventeen days, occurring in the years 1882 to 1889, were 

 selected for comparison, the observatories being those of 

 Toronto, Greenwich, Pawlowsk, Mauritius, Bombay, Batavia, 

 Zi-ka-wei, and Melbourne, and, for a less number of days, 

 Cape Horn (as obtained from the Mission Scientifique du Cap 

 Horn, 1882-83). It was desired to have times for Pola, bu^ it 

 was found that photographic registers during great part of the 

 period did not exist. The variation in time at each place from 

 the mean of times for all places is given for each day. The 

 mean deviation at the different places varies from +2 '4 minutes 

 to -2-9 minutes, the agreement between four of the places — 

 Greenwich, Pawlowsk, Mauritius, and Bombay — being very 

 much closer, the mean values of deviation for Greenwich, 

 Pawlowsk, and Bombay differing, indeed, by only o'l minute, 

 equivalent to 6 seconds. 



The question arises. Are the differences real, or due (con- 

 sidering the contracted time scale) to accidental error ? If the 

 magnetic impulse is really simultaneous over the whole earth, it 

 is a striking physical fact, and if not entirely so, the circum- 

 stance is no less interesting ; but greater attention to accuracy 

 of time scale, or a more extended scale, may be necessary before 

 the point in question can be definitely settled, 



A table is added, showing the character of the magnetic 

 movement at the several observatories, from which it appears 

 that at any one place the movements on different days were 

 in most cases similar, though different at different places, in- 

 dicating on these occasions the occurrence usually of one 

 general type of disturbance. 



Reference is made to the question of earth currents. A com- 

 parison for thirty-one days, between 1880 and 1891, of cases of 

 sudden magnetic movement and earth current at Greenwich, 

 shows the earth current to precede the magnetic movement by 

 0-14 minute, equivalent to 8 seconds. The question of the rela- 

 tion between magnetic movements and earth currents is discussed. 



The desirability of being able temporarily to obtain, when 

 occasion requires, a more extended time scale for all magnetical 

 and meteorological phenomena is pointed out. 



The general result is that in the definite magnetic movements 



' Abstract of paper " On the Simultaneity of Magnetic Variations at different 

 places on occasions of Magnetic Disturbance, and on the relation between 

 Magnetic and Earth Current Phenomena," by William Ellis, F.RJV.S., 

 Superintendent of the Magnetical and Meteorological Department, Royal 

 Observatory, Greenwich. Communicated to the Royal Society, on May 5, 

 1892, by W. H. M. Christie, F.R.S., Astronomer-Royal. 



NO. II 77, VOL. 46] 



preceding disturbance the magnets at any one place are simul- 

 taneously affected ; also that in places widely different in 

 geographical position the times are simultaneous, or nearly so, 

 a small constant difference existing at some places which may 

 be real or may be accidental, but the character of which it 

 seems desirable to determine. It is shown also that at- 

 Greenwich definite magnetic movements are accompanied by 

 earth current movements which are simultaneous, but that 

 neither magnetic irregularities nor ordinary magnetic variations 

 seem to admit of explanation on the supposition of being pro- 

 duced by the direct action of earth currents. 



SCIENTIFIC SERIALS. 



American Journal of Science, May.— Radiation of atmo- 

 spheric air, by C. C. Hutchins. A stream of hot air was ar- 

 ranged so that it could be made to pass in front of one of the 

 faces of a thermopile at a distance of 3 cm., and cause a 

 deflection of a galvanometer needle, or the air could be dis- 

 charged high above the thermopile, leaving it unaffected except 

 by radiation from a large Leslie cube containing water at the 

 temperature of the laboratory. There was no sort of agreement 

 between measures made on eight different days to determine 

 the absolute radiating power of a column of air i centimetre 

 thick at a temperature near 100° C. ; but in an ordinary room and 

 under average conditions the value came out = o*oooooii33 -4- 

 o'ooooooooy 1 1 (/-/')• where /-/' is the difference in tempera- 

 ture between the air and the cube. Tyndall's result, that the 

 radiation increases with the amount of moisture in the air, was 

 confirmed, but no exact law of connection between the two 

 was found. This is probably due to the presence of accidental 

 impurities in the air employed. The increase of radiation 

 proves to be proportional to the increase of temperature. There 

 was a small increase of radiating power when sheets of air more 

 than I centimetre thick were used ; with sheets less than this 

 thickness, no difference of radiation could be detected. — Atmo- 

 spheric radiation of heat and its importance in meteorology, 

 by Cleveland Abbe. In this interesting and exhaustive paper 

 Prof. Abbe brings together practically all the conclusions that 

 have been arrived at on atmospheric movements and their rela- 

 tion to radiation from the air. In his words, " A coinprehensive 

 study of fluid motions shows that air and water alike may be 

 forced to ascend without being warmer and lighter, or to descend 

 without being colder and denser, than the surrounding fluid. 

 The currents and whirls behind any obstacle in streams of air 

 or water are almost wholly independent of differences of density, 

 and are caused by differences of pressure as modified by 

 simple kinetic laws." These motions, which the air is 

 forced to take for purely kinetic reasons, are specially 

 discussed in detail, but it is impossible to enumerate, 

 in an abstract, the many cases considered. — Experiments upon 

 the constitution of certain micas and chlorites, by F. W. Clarke 

 and E. A. Schneider. The minerals analyzed are waluewite, 

 v. of xanthophyllitc, clinochlore, leuchtenbergite, diallage, 

 serpentine, and mica from Miask, Ural.— On the qualitative 

 separation and detection of strontium and calcium by the action 

 of amyl alcohol on the nitrates, by P. E. Browning. — The age 

 and origin of the Lafayette formation, by Eugene W. Hilgard. 

 — On the influence of swamp waters in the formation of the 

 phosphate nodules of South Carolina, by Dr. Charles L. Reese. 

 From the experiments it appears probable that both carbonic 

 acid and the humus substances in fresh-water swamps play an 

 important part both in the accumulation and the concentration 

 of calcium phosphate, and thus in the formation of phosphate 

 nodules, these being considered to be phosphatised marls. — 

 Plattnerite, and its occurrence near Mullars, Idaho, by William 

 S. Yeates ; with crystallographic notes by Edward F. Ayres. — 

 On the occurrence of Upper Silurian strata near Penobscot Bay, 

 Maine, by William W. Dodge and Charles E. Beecher.— Zinc- 

 bearing spring waters from Missouri, by W. F. Hillerbrand. 

 The chief constituent salt in the spring in question is zinc sul- 

 phate. It forms about 56 per cent, of the total dissolved solids. 

 —A meteorite from Central Pennsylvania, by Prof. W. G. 

 Owens. A chemical analysis of the meteorite gave Fe 91*36, 

 Ni 7-56, Co 070, P 0-09, S o-o6, Si trace = 9977.— On two 

 meteoric irons, by G. F. Kunz and E. Weinschenk. One of 

 the masses examined came from Indian Valley Township, Floyd 

 County, Virginia ; the other from Sierra delaTcrnera, Province 

 of Atacama, Chili.— The molecular masses of dextrine and gum 



