1 8 70.] De La Rue, Stewart, and Loewy on Solar Physics. 263 



III. " Researches on Solar Physics. — No. II. The Positions and 

 Areas of the Spots observed at Kew during the years 1864-66, 

 also the Spotted Area of the Sun's visible disk from the com- 

 mencement of 1832 up to May 1868." By Warren De La 

 Rue, Esq., Ph.D., F.R.S., F.R.A.S., Balfour Stewart, Esq., 

 LL.D., F.R.S., F.R.A.S., Superintendent of the Kew Obser- 

 vatory, and Benjamin Loewy, Esq., F.R.A.S. Received Fe- 

 bruary 15, 1870. 



(Abstract.) 



The paper commences with a continuation for the years 1864-66 of 

 Tables II. and III. of a previous paper by the same authors ; it then pro- 

 ceeds to a discussion of the value of the pictures of the sun made by 

 Hofrath Schwabe, which had been placed at the disposal of the authors, 

 and the result is that these pictures, when compared with simultaneous 

 pictures taken by Carrington and by the Kew heliograph, are found to be of 

 great trustworthiness. From 1832 to 1854 the pictures discussed are those 

 of Schwabe, who was the only observer between these dates ; then follows the 

 series taken by Carrington, and lastly the Kew series, which began in 1862. 



A list is given of the values of the sun's spotted area for every fortnight, 

 from the beginning of 1832 up to May 1868, and also a list of three- 

 monthly values of the same, each three-monthly value being the mean of 

 the three fortnightly values which precede and of the three which follow 

 it. These three-monthly values are also given for every fortnight. 



A plate is appended to the paper, in which a curve is laid down repre- 

 senting the progress of solar disturbance as derived from the three-monthly 

 values ; and another curve is derived from this by a simple process of equali- 

 zation, representing the progress of the ten-yearly period. The values of 

 the latter curve, corresponding to every fortnight, are also tabulated. From 

 this Table are derived the following epochs of maxima and minima of the 

 longer period : — 



Minimum Nov. 28, 1833. 



Maximum Dec. 21, 1836. 



Minimum Sept. 21, 1843. 



Maximum Nov. 14, 1847. 



Minimum April 21, 1856. 



Maximum Sept. 7, 1859. 



Minimum Feb. 14, 1867. 



This exhibits a variability in the length of the whole period. 



Thus we have between 1st and 2nd minimum 9*81 years. 



2nd and 3rd do 12'58 „ 



3rd and 4th do 10'81 „ 



Mean of all the periods 11*07 years. 



iinother fact previously noted by Sir J. Herschel is brought to light, 



