MARYLAND GEOLOGICAL SURVEY

455

TABLE I.

Mean hourly values of the magnetic declination at the Washington Magnetic Observatory

during the year 1890.

4° West+tabular quantity.

	Hour.	Jan.	Feb.	Mar.	Apr.	May	June.	July.	Aug.	Sept.	Oct.	Nov.	Dec.	Mean.
	1 A. M.	4'. 0	3/. 9	3'. 9	4'. 3	4'. 6	5'. 0	5'. 6	5'. 7	6'. 1	6'. 6	8'. 3	9'. 7	5'. 5
	2	4. 0	4. 3	3. 9	4. 0	4. 6	5. 1	5. 0	5. 7	5. 8	6. 8	7. 6	8. 1	5. 4
	3	4. 1	3. 9	4. 1	3. 6	4. 2	4. 9	5. 6	5. 9	5. 5	6. 3	7. 9	7. 9	5. 3
	4	3. 7	3. 7	3. 9	3. 3	4. 0	4. 8	5. 5	4. 7	5. 3	6. 4	7. 3	7. 4	5. 0
	5	3. 8	3. 7	3. 5	3. 2	3. 2	3. 8	4. 2	4. 4	5. 1	7. 0	7. 5	7. 7	4. 8
	6	4. 1	3. 5	3. 3	2. 2	2. 2	2. 4	2. 6	2. 6	4. 1	6. 5	7. 3	7. 5	4. 0
	7	3. 6	3. 3	2. 2	1. 4	2. 0	1. 2	1. 2	0. 6	2. 5	5. 0	6. 9	7. 5	3. 1
	8	2. 7	2. 6	1. 2	l. O	1. 6	1. 0	1. 1	0. 2	2. 1	3. 4	6. 2	7. 9	2. 6
	9	1. 4	2. 2	l. O	1. 7	2. 6	2. 0	1. 9	1. 9	3. 4	3. 6	6. 5	6. O	2. 9
	10	1. 4	2. 2	2. 6	3. 9	5. 0	4. 4	4. 1	5. 9	5. 2	5. 2	7. 1	6. 0	4. 4
	11	3. 0	3. 2	4. 7	6. 5	6. 8	8. 5	6. 6	8. 7	8. 2	7. 4	8. 4	7. 4	6. 6
	Noon,	5. 2	4. 9	6. 8	8. 9	7. 4	9. 5	9. 2	11. 0	10. 4	9. 6	9. 9	9. 0	8. 5
	1	6. 8	6-2	7. 9	9. 4	1O. 2	10. 6	1O. S	11. 4	11. 1	10. 6	1O. 6	10. 0	9. 6
	2	7. O	6. 8	8. 1	9. 4	10. 0	1O. 6	10. 2	10. 9	10. 9	10. 6	10. 3	10. 1	9. 6
	3	6. 3	6. 7	7. 6	8. 5	8. 9	9. 8	9. 7	9. 5	9. 8	9. 7	9. 5	9. 8	'8. 8
	4	5. 4	5. 8	6. 5	7. 0	7. 2	8. 4	8. 5	7. 8	8. 6	8. 5	8. 9	9. 2	7. 6
	5	4. 6	5. 1	5. 6	5. 8	5. 8	7. 1	7. 2	6. 8	7. 4	7. 6	8. 8	8. 3	6. 7
	6	4. 0	5. 0	5. 0	5. 0	5. 2	6. 3	6. 1	5. 9	6. 9	7. 2	8. 2	7. 7	6. 0
	7	3. 8	3. 6	4. 6	4. 8	5. 4	6. 0	5. 8	6. 0	6. 6	6. 6	7. 3	7. 4	5. 7
	8	3. 5	3. 7	4. 4	4. 4	5. 4	5. 8	5. 5	5. 9	5. 6	6. 2	6. 7	7. 1	5. 4
	9	3. 3	3. 5	3. 9	4. 4	4. 9	5. 8	5. 1	5. 8	5. 8	5. 2	6. 3	6. 8	5. 1
	10	2. 8	3. 2	3. 4	4. 2	4. 9	5. 8	5. 3	5. 7	5. 8	6. 0	5. 8	7. 1	5. 0
	11	3. 0	3. 3	3. 6	4. 0	4. 9	5. 2	5. 3	5. 8	5. 8	6. 2	6. 3	7. 3	5. 0
	Midn't,	3. 5	3. 4	3. 8	4. 0	4. 7	5. 3	5. 3	6. 0	5. 9	6. 0	6. 7	7. 4	5. 2
	Mean,	4. 0	4. 1	4. 4	4. 8	5. 2	5. 8	5. 7	6. 0	6. 4	6. 8	7. 8	7. 9	5. 8
	Range,	5. 6	4. 5	7. 1	8. 4	8. 7	9. 6	9. 3	11. 2	8. 9	7. 2	4. 4	4. 1	7. 0

The diagram (Fig. 3) gives a graphical representation of the diur-
nal variation, on the average for the year, for the years 1888, 1889
and 1890. As will be seen, the chief characteristics of this remark-
able variation are, first, that at about sunrise the north end of the
needle swings to the eastward until about 8 or 9 A. M., when it has
reached its most easterly elongation. If the declination is west of
north, as it is at present, over the entire state, then the declination
will have reached its lowest value for the day at this time. Secondly,
the needle, after hovering about the easterly extreme for a while, turns
about and begins to march westward. About 10 or 11 A. M. it crosses
the mean or average position for the entire day (24 hours). It does
not stop here, but still pursues its onward march and at this moment
with the greatest velocity until about 1 to 2 P. M., when the most