The New Astronomy

by S. P. Langley

Chicago, Nov. 17.—An electric storm of the greatest violence raged in all the territory to points beyond Omaha.... The switch-board here has been on fire a dozen times during the forenoon. At noon only a single wire out of fifteen between this city and New York was in operation.

And so on through a column.

3. In [Fig. 50] we give a portion of the automatic trace of the magnetic needles at Greenwich.[3] These needles are mounted on massive piers in the cellars of the observatory, far removed from every visible source of disturbance, and each carries a small mirror, whence a spot of light is reflected upon a strip of photographic paper, kept continually rolling before it by clock-work. If the needle is still, the moving strip of paper will have a straight line on it, traced by the point of light, which is in this case motionless. If the needle swings to the right or left, the light-spot vibrates with it, and the line it traces becomes sinuous, or more and more sharply zigzagged as the needle shivers under the unknown forces which control it.

[3] It appears here through the kindness of the Astronomer Royal. We regret to say that American observers are dependent on the courtesy of foreign ones in such matters, the United States having no observatory where such records of sun-spots and magnetic variation are systematically kept.

The upper part of [Fig. 50] gives a little portion of this automatic trace on November 16th before the disturbance began, to show the ordinary daily record, which should be compared with the violent perturbation occurring simultaneously with the telegraphic disturbance in the United States. We may, for the reader’s convenience, remark that as the astronomical day begins twelve hours later than the civil day, the approximate Washington mean times, corresponding to the Greenwich hours after twelve, are found by adding one to the days and subtracting seventeen from the hours. Thus “November 16th, twenty-two hours” corresponds in the eastern United States nearly to five o’clock in the morning of November 17th.

The Allegheny observer, it will be remembered, in his glimpse of the spot on November 16th, was struck with the great activity of the internal motions then going on in it. The Astronomer Royal states that a portion of the spot became detached on November 17th or 18th, and that several small spots which broke out in the immediate neighborhood were seen for the first time on the photographs taken November 17th, twenty-two hours.

“Are we to conclude from this,” it may be asked, “that what went on in the sun was the cause of the trouble on the telegraph wires?” I think we are not at all entitled to conclude so from this instance alone; but though in one such case, taken by itself, there is nothing conclusive, yet when such a degree of coincidence occurs again and again, the habitual observer of solar phenomena learns to look with some confidence for evidence of electrical disturbance here following certain kinds of disturbance there, and the weight of this part of the evidence is not to be sought so much in the strength of a single case, as in the multitude of such coincidences.

We have, however, not only the means of comparing sun-spot years with years of terrestrial electric disturbance, but individual instances, particular minutes of sun-spot changes, with particular minutes of terrestrial change; and both comparisons are of the most convincing character.

First, let us observe that the compass needle, in its regular and ordinary behavior, does not point constantly in any one direction through the day, but moves a very little one way in the morning, and back in the afternoon. This same movement, which can be noticed even in a good surveyor’s compass, is called the “diurnal oscillation,” and has long been known. It has been known, too, that its amount altered from one year to another; but since Schwabe’s observations it has been found that the changes in this variation and in the number of the spots went on together. The coincidences which we failed to note in the comparison of the spots with the prices of grain are here made out with convincing clearness, as the reader will see by a simple inspection of this chart ([Fig. 51], taken from Professor Young’s work), where the horizontal divisions still denote years, and the height of the continuous curve the relative number of spots, while the height of the dotted curve is the amount of the magnetic variation. Though we have given but a part of the curve, the presumption from the agreement in the forty years alone would be a strong one that the two effects, apparently so widely remote in their nature, are really due to a common cause.