40 Dr. Bottomley on the late 



days. These results suggested the idea that the variable 

 period thus found was in some way connected with and 

 dependent upon the great solar spot period, the minimum 

 value occurring in the year of minimum frequency of the 

 solar spots and the maximum values in the years when the 

 spots were most numerous. Several series of thermo- 

 metrical observations were now examined for indications 

 of periodical changes in the element of mean daily tempe- 

 rature, and it was found that they exhibited with unexpected 

 distinctness changes in the element, occurring also in a 

 variable period, the range of variation, however, being 

 somewhat less than in the case of the magnetic element, 

 although the times of maximum and minimum were almost 

 exactly the same. The maximum and minimum values 

 were respectively 31 and 23^^ days. He also refers to 

 another period having a mean duration of rather over 

 eighteen months first observed in discussing the Greenwich 

 magnetical observations for the years 1848 to 1859. In 

 this paper he regards all the movements of the magnet, 

 whether large or small, as having a common origin. General 

 Sabine separates the larger movements from the gross mass 

 and treats them as extraordinary disturbances. With 

 regard to the variability of the short period, he thinks that 

 the facts would perhaps be best explained by supposing (i) 

 that a ring of nebulous matter exists differing in density or 

 constitution in different parts, or several masses of such 

 matter forming a discontinuous ring, and circulating round 

 the sun in a plane nearly coincident with the plane of the 

 ecliptic, and at a mean distance from the sun of about one- 

 sixth of the radius of the earth's orbit ; (2) that the attractive 

 force of the sun on the matter of the ring is alternately 

 increased and diminished by the operation of the force which 

 produces the solar spots being greatest at the time of 

 minimum solar spot frequency, and least when the spots are 

 most numerous ; (3) the attractive force being variable, the 



