Page:Scientific Memoirs, Vol. 2 (1841).djvu/75

Mean Fluctuation of the Magnetic Declination during the three years from 1834 to 1837.

	8, a. m.			Mean.	1, p. m.			Mean.
	I.	II.	III.		I.	II.	III.
April	74	126	205	147	129	101	264	180
May	192	124	277	207	158	183	210	185
June	172	171	199	181	95	151	217	162
July	213	243	287	250	119	184	252	193
August	264	253	269	262	175	165	307	225
September	162	325	207	241	172	143	161	159
October	116	296	216	222	182	202	242	210
November	79	205	308	218	170	173	126	158
December	132	324	71	206	184	206	154	182
January	146	274	138	196	174	212	154	181
February	116	146	164	143	178	183	129	165
March	100	109	366	228	127	153	246	183
Mean	157	229	238	211	156	174	213	183

In reference to the single observations, Ave may here mention the greatest fluctuations which have occurred in the course of three years, in the forenoon and afternoon declinations. The greatest forenoon fluctuation was on the 8th of October, 1835, when the declination was about 20′ 1″ greater than on the 7th of October; and the greatest afternoon fluctuation occurred on the 24th of April, 1836, when the declination was 13′ 0″ greater than on the preceding day. On the other hand, perfect equality either of the forenoon or of the afternoon declinations, for two successive days, is a circumstance which has frequently occurred. In the monthly mean fluctuations these extremes naturally come much closer together; nevertheless, the great dissimilarity of the single months in this respect is still very remarkable, since, according to the above general view, the mean fluctuation in the forenoon declination in March, 1837, amounted to 6′ 6″; in December, 1836, only to 1′ 11″.

Whether, in general, greater fluctuations prevail at one time of the day than at others, cannot be determined with certainty, from the results of our observations of 8 a.m. and 1 p.m. Both are nearly equal in mean fluctuation for the first year; in the two following years the forenoon fluctuations exceed in amount, but the difference in the final results from the three years, 3′ 31″ and 3′ 3″, is too small to allow of any conclusion being yet {{hws|esta|established}