474 Coimbra Monthly Magnetic Determinations. [May 9, 



not restricted to locality is proved by the Greenwicli Tables, in whicli 

 these groups stand out still more prominently (see Table VII.) ; the ratios 

 between warm and cold being 9 to 1 in the first decade, and 1 to 9 in the 

 second. It is difficult therefore to avoid the conclusion that, during the 

 twenty years in question, the Novembers were exceptional months at both 

 places ; although at Guernsey they were more frequently followed by un- 

 favourable Junes. 



The Greenwich diagram (Diagram II. Archives), to which I must now 

 briefly advert, does not exhibit so striking a contrast of light and shade as 

 was observable at first sight in the other diagram. But on further exami- 

 nation it will be found that the warm months of the first decade correspond 

 nearly in number with the cold months of the second, although not so 

 exactly as at Guernsey. 



Months. Degrees. 



' ^ ^ ^ ^ 



n . 1 f 1st decade. 65 warm to 55 cold. 157°'5 plus to 108°-5 minus, 

 ureenwicn. | decade. 62 cold to 58 warm. 148"-4 minus to 116''-8 plus. 



On comparing the above abstract with that in a previous page, it will be 

 perceived that the disparity between the general results, from both places, 

 is not very considerable ; a similarity all the more remarkable, when we 

 consider the great difference in position and latitude of the inland and the 

 insular stations. See Diagram III. 



It would be superfluous to enter into any further discussion of the 

 various alternations which the coefficients are susceptible of, in a paper 

 which is merely intended to direct attention to the accompanying diagrams 

 and analytical tables. My motive for venturing to bring them under notice 

 is a desire to place them in the hands of those better qualified than I am 

 for conducting processes of induction ; and as the modified plan I have 

 adopted is based upon long recognized principles, which are applicable to 

 the investigation of atmospheric phenomena in any locality, I trust that it 

 may be deemed worthy of consideration. 



IV. ^''Monthly Magnetic Determinations^ from June to November 

 1 866 inclusive, made at the Observatory at Coimbra/'-' by Professor 

 J. A. DE SoTJZA, Director of the Observatory. Communicated 

 (with a Note) by the President. Received May 8, 1867. 



[Note. — These observations contain the record of the commencement 

 of the absolute magnetic determinations at the Coimbra Observatory, with 

 instruments procured by M. de Souza at Kew, and on the system of 

 observation and reduction adopted at the Kew Observatory. The employ- 

 ment of the photographic continuously self-recording instruments at 

 Coimbra has hitherto been delayed by the works required for the introduc- 

 tion of gas into the Observatory ; but this has now been accomplished ; and 

 a letter, dated April 20, 1867, from the Director states that the photo- 



