Proceedings of the British Association. 157 



hope of determining differences of longitude by means of the 

 corresponding movements of the magnet at the two stations. 

 The changes observed in the observations at present under con- 

 sideration, were however far greater in magnitude, and placed 

 the phenomenon in a much stronger light. The last circumstance 

 to which Mr. L. invited attention was, that the curves of horizon- 

 tal intensity presented, at remote stations, a much nearer agree- 

 ment than those of declination : from which it may be inferred 

 that a true knowledge of the nature and laws of the disturbing 

 causes will be better attained by the examination of intensity 

 changes, (including, of course, those of the vertical intensity,) 

 than those which are dependent solely on the direction of the 

 acting forces. 



The President also laid on the table the curves representing 

 the changes of magnetic declination, observed at Cambridge, 

 Massachusetts, by Mr. W. C. Bond and Prof J. Levering, on the 

 term-days of May and October, 1840. The corresponding obser- 

 vations made at Toronto by Lieut. Riddell, were laid down in a 

 curve in connection with the latter. The results exhibited the 

 same close agreement in the forms of the curves, and in the 

 epochs of the successive maxima and minima as had been already 

 noticed in Europe, although, (as before remarked,) all resemblance 

 between this and the European system of changes is nearly ob- 

 literated. Cambridge is distant about five hundred miles from 

 Toronto : the mean declination at the former place is now" 9° 20' 

 West. 



Sir D. Brewster presented the following report on the State of 

 the Inquiry into the action of gaseous and, other Media on the 

 Solar Spectrum. In prosecuting this inquiry, my attention has 

 been principally directed to the action of the earth's atmosphere 

 upon the solar spectrum, and I hope to be able to present to the 

 next meeting of the Association a map of the bands produced by 

 atmospheric absorption. I have also made considerable progress 

 in constructing a map of the spectrum containing the numerous 

 lines and bands produced by the action of nitrous gas. In sub- 

 mitting to examination several other gaseous media, my results 

 have been principally of a negative character ; but in my experi- 

 ments with solid and fluid media, I have been led to many posi- 

 tive and interesting results. In order to obtain additional accu- 

 racy of observation, particularly near the extremities of the spec* 



