542 



REPORT — 1901. 



possible to drive the cords from the commutator barrel by gravity. The method 

 could not be conveniently used except under like circumstances of elevation. 



To operate the instruments at Singkep, Netherlands Indies, was a very diiferent 

 problem, and led to the devising of two improvements in this type of mechanical 

 commutator which make it universally adaptable to the needs of both astronomers 

 and physicists : — 



(«) Instead of a single barrel or drum I used as many drums as there were 

 instruments to be operated. Each drum was provided with a collar and set-screw, 

 so that the process of adjusting one instrument and its automatic movements did 

 not disturb the adjustments of othei's already made. 



(d) Instead of gravity as a power to turn the drums, they were turned by 

 hand, timed accurately to the motion of a pendulum ; and the commutator cords, 

 after unwinding from the several drums and doing their work in tripping the 

 escapements, were returned over pulleys, each to its individual drum, where they 

 wound up on one side just as fast as they unreeled from the other. This simple 

 arrangement easily gave accommodation for the 80 feet of cord required by the 

 6m. 20s. duration of totality. 



4. The Drift in Longitude of Groups of Faculoi on the Sufi's Surface. 

 By the Rev. A. L. Cortie, S.J., F.R.A.S. 



From a discussion of the Potsdam photographs for the year 1884, Wilsing con- 

 cluded that faculse did not show the drift in longitude with decrease in latitude 

 exhibited by sun-spots. An opposite conclusion was derived from plates covering 

 the period 1891-94 at Pulkowa, by Statonofl". On these plates no facula was 

 followed for more than three days, and the measures were made on selected points 

 in the faculous groups. From the study of selected groups of facula? in the year 

 1889, Father Sidgreaves showed that groups considered as a whole during long 

 periods of time drifted with the spots. The present paper is supplementary to 

 that of Father Sidgreaves, and while traversing the same ground, gives a more 

 detailed discussion of the observations. Moreover, it is illustrated by diagrams 

 which show the drift in a very convincing way. The periods of time during which 

 the faculae were followed ranged from 19 to 120 days. The year 1889 was 

 selected as being a minimum year of solar activity, and therefore presenting less 

 difficulty for the identification and following of the several groups of faculee than 

 in a maximum year. Moreover, to malve identification certain, of 121 groups 

 drawn and measured during that year, all but thirteen were excluded. These 

 latter groitps were all connected with sun-spots, and passed through the various 

 phases of growth which characterise such groups. In the study of the drift, 

 Carrington's method, set forth in his ' Observations of Solar Spots,' was exactly 

 followed. A centre of each group was chosen winch appeared to give the most 

 trustworthy result for diurnal motion. But every member of each group had pre- 

 viously been put down in its true heliographic position on a set of charts, one to 

 each solar rotation. The positions were determined from the original drawings by 

 means of a series of accurate heliographic projections. The Table gives the 

 results from the measurements. 



