Section III., 1892. [ 29 ] Trans. Eoy. Soc. Canada. 



IV. — Observations of Sunspofs at McGill College Observatory. 



\ 

 By Prof. C. H. McLeod, Ma. E. 



(Communicated by Dr. A. Johnson ; read May, 1891.) 



The observations summarized in the accompanying table haA-e been made in continua* 

 tion of those on which a note was presented to the Royal Society at its last meeting. The 

 methods of observation need not here be repeated, beyond a mere statement that the 

 sun's image is projected and enlarged to a diameter of 8 in., on a screen attached to an 

 equatorially mounted telescope. 



The first column in the table gives the date of the commencement of the synodic 

 rotation of the sun, i.e., the time of the coincidence of the assumed prime meridian with 

 the central meridian, the period of the sun's sidereal rotation being taken as 25-38 days. 

 The dates are given in Greenwich civil time reckoning from midnight. The average 

 number of spots per day have been obtained by dividing the total number of spots 

 observed, in a rotation, by the number of days in which the observations were made 

 during the rotation. The other columns of the table are self-explanatory. 



It will be observed from the table and diagram that the average positions of the spots 

 have approached the equator, somewhat; more particularly to the north where there is a 

 decided tendency towards a reduction of latitude. During 1889 and the first months of 

 1890, the zones of latitude between 10^ and 20° were almost wholly free from spots. This 

 cannot be said with regard to the present period as the spots have been fairly well distri- 

 buted, in the north between the limits 8" and 24°, and in the south between 4° and 33". In 

 the southern hemisphere one important group and two isolated spots fell between 4° and 

 10'. In the north two groups appeared just within 10' of the equator, and one of 

 these, seen from Feb. 10th to Feb. 13th, attained a total area of 120 millionths of the sun's 

 hemisphere, being amongst the most important groups of the year. Since the spots 

 occurring towards the end of a period are found almost wholly within 10° of the equator, 

 and those occurring at the beginning of a new period, or after the passage of the mini- 

 mum, are almost wholly beyond 20' in latitude, the spots within the limits of 10° from 

 the equator which appear after the passage of the minimum have usually been regarded 

 as old cyclespots, giving an appearance of overlapping of the two periods. This was dis- 

 tinctly marked towards the end of 1889, while for the first seven months of 1890, there 

 were no old cyclespots. The minimum period would from these circumstances appear to 

 have occurred about the middle of the year 1889, and it has been so placed by Mr. 

 Maunder of the Royal Observatory, G-reenwich. An inspection of the tables does not, 

 however, seem to bear out this view and would go to show that in so far as spot fre- 

 quency is concerned the minimum period should be placed at the beginning of 1890. The 

 spots which have recently reappeared within the 10° zone can scarcely be regarded as 



