168 



Mr. Balfour Stewart on Sun Spots. 



[Mar. 17, 



conductors. The moment we pass from the metals to their compounds, we 

 pass from a series of good conductors to bad ones, and from bad radiators 

 to good ones. Water, among liquids, is probably the worst conductor ; it 

 is the best radiator. Silver, among solids, is the best conductor ; it is the 

 worst radiator. In the excellent researches of MM. De la Provostaye and 

 Desains the author finds a striking illustration of what lie regards as a 

 natural law — that those molecules which transfer the greatest amount of 

 motion to the ether, or, in other words, radiate most powerfully, are the 

 least competent to communicate motion to each other, or, in other words, 

 to conduct with facility. 



II. " Remarks on Sun Spots.^^ By Balfour Stewart, M.A., F.K.S., 

 Superintendent of the Kew Observatory. Received March 8, 

 1864. 



In the volume on Sun Spots which Carrington has recently published, 

 we are furnished with a curve denoting the relative frequency of these phe- 

 nomena from 1760 to the present time. This curve exhibits a maximum 

 corresponding to 1 788*6. Again, in Dalton's ' Meteorology ' we have a list 

 of aurorse observed at Kendal and Keswick from May 1786 to May 1793. 



The observations at Kendal were made by Dalton himself, and those at 

 Keswick by Crosthwaite. This list gives — 



For the year 1 787 .... 27 aurorae, 

 1788.... 53 „ 

 1789 45 „ 



For the year 1 790 .... 36 aurorae; 



1791.... 37 „ 

 1792.... 23 „ 



showing a maximum about the middle, or near the end of 1788. This 

 corresponds very nearly with 1788*6, which we have seen is one of Car- 

 rington' s dates of maximum sun spots. 



The following observation is unconnected with the aurora borealis. In 

 examining the sun pictures taken with the Kew Heliograph under the 

 superintendence of Mr.De la Rue, it appears to be a nearly universal law that 

 the faculse belonging to a spot appear to the left of that spot, the motion 

 due to the sun's rotation being across the picture from left to right. 



These pictures comprise a few taken in 1858, more in 1859, a few in 1861, 



and many more in 1862 and 1863, and they have been carefully examined 



by Mr. Beckley, of Kew Observatory, and myself. The following Table 



expresses the result obtained : — 



No. of cases of No. of cases of No. of cases of No. of cases of fa- 

 Year, facula to left facula to right facula equally on culae mostly be- 

 of spot. of spot. both sides of spot. tween two spots. 



1858 2 • 



1859 18 3 



1861 9 1 3 



1862 64 4 7 3 



1863 47 9 2 



1864 18 1 2 1 



