lines of equal magnetic declination (variation) run very irregularly over the region embraced by the Piedmont Plateau (central and northeastern Maryland), while over the Coastal Plain (southern and southeastern Maryland) they are fairly regular. The counties that are especially disturbed are Cecil, Harford, Baltimore, Carroll, Howard, Montgomery and Frederick. In the regions covered by these counties the density of the stations must be greatly increased before we can be sure of giving a true representation of the distribution of the earth's magnetism as manifested by the declination.' Additional observations made since the drawing of these lines, especially in Harford County, clearly demonstrate that little dependence can be put upon lines constructed from a small number of stations. The line 6° W. as at present sketched must be regarded as but a rough approximation to the truth. A more detailed investigation in this region will result in a number of closed areas, where the values will be smaller or larger than those obtained by direct interpolation. Thus east of line 6° W. there are a number of places where the declination drops down to 50 and less, whereas the values should have been greater. For example, Elkton gives but 50.4 for 1900. The line 6° W., as at present projected, is doubtless not far from the position which the line would have were it not for the marked disturbances referred to. Its general direction harmonizes with that as indicated by the distant observations in Pennsylvania.

The same marked anomalies in the distribution of the earth's magnetism have been revealed by the other preliminary magnetic map, viz., the map giving the lines of equal magnetic inclination and the (Plate XVI) lines of equal horizontal magnetic force. These preliminary maps have served a useful purpose in guiding me in the map

1 The results thus far obtained from the work of the present year clearly indicate that the curves presented in this report have not exaggerated the amount of disturbance in the distribution of the earth's magnetism over the counties enumerated. Thus, for example, the declinations observed at Linden and Rockville-both in Montgomery county and distant from each other seven miles-differ from each other by nearly two degrees. At Linden the declination for January 1st, 1900, will be 3°.6 and for Rockville 5°.5. It will be seen that the isogonic line (42°)-drawn before the Rockville observations were made-would represent a mean of the two stations for this locality quite satisfactorily.

ping out of the work of the present year. It will be interesting to trace the further progress of the line of equal magnetic inclination 71°. Special stress is to be laid this year upon the investigation of the regional disturbances.

It will be noticed that at present the declination is westerly over the entire area of the state, ranging from a little over 6° west in the northeast to about 31° in the extreme west. The distribution of the declination has, however, not always been thus.

ISOGONIC CHARTS FOR 1700 AND FOR 1800.

[Plate XVII.]

With the aid of the table, XII, giving the approximate values of the magnetic declination at the various county-seats from 1700 to 1900, and with the aid of the long series of observations in the adjoining states, I have been able to construct isogonic charts for 1700 and for 1800 with a fair degree of accuracy. It will be seen that for 1700 the lines of equal magnetic declination are about the same as those for 1900. In other words, in the first decade, approximately, of the eighteenth century the needle pointed in precisely the same direction as at present. But this did not occur simultaneously over the entire state; hence the isogonic chart, while closely approximating the 1900 chart, would not be exactly the same.

The lines for 1800, however, present a vastly different appearance. We now have a central line the so-called agonic line (line of no declination) along which the needle was "true to the pole." East of this line the needle bore by a small amount west of true north, while west of the line the needle pointed east of true north.

THE SECULAR MOTION OF THE AGONIC LINE OVER MARYLAND. When did the line of no declination enter the state and when did it leave it? Was its position in 1800 the extreme easterly one? These are questions that we can again answer with the aid of the table XII. Turning back to it we obtain the following facts:

We thus see that the line of no declination entered the state in about 1769 and thereupon marched eastward until it reached an extreme easterly position a few miles east of Washington in about 1805. It then began to recede, now marching westward until in about 1850, when it left the state. The average annual motion in longitude for the forward and the backward march was about the same-0°.7, or about 37 miles. The next map (Fig. 7) exhibits the motion of the agonic line over the eastern part of our country for various epochs, as drawn by Mr. Schott. It will be noticed that our deductions are in harmony with the facts set forth by this map.

It would appear, then, as though the needle did not point east of north between 1700 and the present date in the greater part of Maryland. It should be mentioned, however, that there may have been regions east of the extreme easterly position assumed by the agonic line where the needle in the early part of the eighteenth century was either true to the pole" or bore by a small amount east. This occurred in the magnetically disturbed areas of Maryland and was due to the fact that in those regions the declination has a smaller value than it would have if the causes of the disturbances did not exist. Thus, for example, we find that at Elkton in about 1800 the direction. of the needle practically coincided with the true meridian, whereas if the declination had been normal it would have been about 110 west. It is this fact undoubtedly which makes the matter of re-locating old surveys of such especial difficulty in the northeast counties. There are disturbed and undisturbed areas in these counties. Over the former the needle may have pointed east at beginning of present century; over the latter, which may be within a very short distance of the former, the needle pointed west. Granted that over this region compass surveying should be prohibited in the future by the state, the difficulty will always remain in the proper re-location of the old surveys referred to compass bearings.

THE EFFECT OF THE SECULAR VARIATION OF THE MAGNETIC MERIDIANS. If in the year 1800 the northern boundary of Maryland-the famous Mason and Dixon line-had been laid out with the compass