238 



Senhor Capello on the reappearance [Jan. 21, 



Group I, Excesses not exceeding 4 scale-units. 



IT. Excesses exceeding 4 and not exceeding 9 scale-units. 



III. Excesses exceeding 9 and not exceeding J 9 scale-units. 



IV. Excesses above 19 scale- units. 



Group I. 



Group II. 



Group III. 



Group IV. 



Excess 

 (under 5). 



Abruptness. 



Excess 



I'll ndpr 1 (Vl 



6 

 G 

 8 

 5 

 8 

 5 

 7 

 9 

 5 



Abruptness. 



Excess 



( it n *1 p>v 90^i 



Abruptness. 



Excess 



( du<)> - tv;. 



Abruptness. 



2 

 2 



o 





 



1 

 4 

 3 



3'7 

 G-4 



4- 

 3-1 

 3-i 



2- 9 

 1-8 



3- 3 



5- 2 



4-2 



2- 6 

 6-3 



3- 3 

 8-7 

 35 

 6.3 



4- 7 

 4-1 



10 

 10 



11 



10 

 10 

 15 

 11 

 13 



7'5 

 2-0 

 8-7 

 12-0 

 2-8 



6- 4 

 49 



7- 4 



21 



25 

 25 

 20 

 21 

 21 

 22 

 24 



7-5 

 2-9 

 10-7 

 7-0 



6- 6 

 11/2 



9-G 



7- 8 



Means 1*5 



37 



6-6 



4-9 



11 



6-5 



22 



7-9 



It would appear from these groups that generally, and on an average, 

 the excess of Stonyhurst over Kew in declination disturbances varies with 

 the abruptness of the disturbance, being great when the disturbance is very 

 abrupt. 



It is hoped that on some future occasion further results, derived from an 

 intercomparison of these curves, may be presented to the Society. 



III. " On the reappearance of some periods of Decimation Disturbance 

 at Lisbon during two, three, or several days." By Senhor 

 Capello, of the Lisbon Observatory. Communicated by Bal- 

 four Stewart, LL.D. Received October 28, 1868. 



Any one who carefully examines the magnetograph curves must often 

 notice that there are, during, periods of disturbance, synchronous move- 

 ments of the needle during corresponding hours for two, three, or more 

 days. 



In some cases the repetition is only in two or three parallel movements, 

 in others there are true periods of some hours in duration. 



The repeated periods are not entirely similar, their phases being in 

 general so modified that in some cases their identity can only be recog- 

 nized by a very minute investigation. 



The same periods, when repeated, have not always the same total dura- 

 tion ; nor do they recommence at the same precise hour, but sometimes 

 earlier, and sometimes later, the differences varying from a few minutes to 

 two or three hours. 



There is also to be remarked in the repeated disturbances a tendency to 

 modify in form, or to level their peaks and hollows, or, on the contrary, to 

 augment the angular forms. 



