379 



quantity; indeed it is not very easy to obtain it at any time. 

 However, 1 hope to be able to add something more important, 

 particularly vpith reference to the nature of wax and its con- 

 nexion with pollen, at the next meeting of the Academy." 



The President made a short communication on the relation 

 of the Variations of the Magnetic Elements (diurnal and an- 

 nual) to the contemporaneous Variations of Temperature. 



Having already shown* that the changes of the magne- 

 tic declination, and those of temperature, were connected 

 in the most intimate manner, the author was naturally led 

 to expect a similar correspondence in the case of the other 

 magnetic elements. This expectation has been fully confirmed, 

 so far as relates to the intensity of the horizontal component 

 of the magnetic force. Upon a comparison of the results of ob- 

 servation of this element for the four years (1840-1843) already 

 discussed, he has found that the diurnal range of the intensity 

 (or the area of the diurnal curve, which observes a similar 

 law) undergoes a change in the course of the year analogous 

 to that which has been already found in the case of the declina- 

 tion, and, therefore, like it, closely resembling the correspon- 

 ding variation of the range of temperature. The minimum range 

 of the intensity (like that of the declination and temperature) 

 occurs in December. There are two maxima, with a small 

 intervening minimum ; the first of these occurs (as in the 

 case of the declination) in April, and the second in July. 



The mean diurnal ranges of the intensity, in the separate 

 years, likewise follow a progression similar to that of the tem- 

 perature, being greatest in the first of the four years above 

 mentioned, and diminishing thence unto the last. 



The annual variation of the horizontal intensity is, in like 

 mannpr, closely connected with the corresponding variation of 



* Results of Observations made at the Magnetical Observatory of Dublin, 

 (First Series.) Trans. R. I. A., vol. xxii. part i. 

 VOL. IV. 2 F 



