261. 



transverse sections made. He states that neither Ben 

 Nevis in Scotland, Snowdon in Wales, nor Macgillycuddie's 

 Reeks in Ireland, have had their heights ascertained by 

 actual levelling ; and he observes, that were these heights 

 accurately determined, further knowledge might then be ob- 

 tained regarding refraction, and the measurement of altitudes 

 by the barometer. A small map of the island of Inish Turk, 

 on which are delineated lines of equal level, accompanies 

 the paper. 



In conclusion, Mr. Bald observes, that a model of a 

 country in the hands of the topographic, military, civil, or 

 mining engineer, could be applied to a variety of useful 

 purposes ; and particularly that it would enable young men 

 to shade accurately topographic maps, a thing that has not 

 yet, to his knowledge, been systematically attended to in any 

 of the institutions of Great Britain or Ireland. 



Rev. H. Lloyd, V. P., read a paper " on the relative 

 Position of three Magnets, in a Magnetical Observatory." 



It is a problem of much importance, in connexion with the 

 arrangement of a magnetical observatory, to determine the 

 relative position of the magnetical instruments in such a man- 

 ner, that their mutual action may be either absolutely null, 

 or at least, readily calculable. Such was stated by the 

 author to be the object of the investigation now laid before 

 the Academy. 



In the case of two horizontal magnets, one of which (in- 

 tended for observations of declination) is in the magnetic me- 

 ridian, and the other (used for observations of horizontal in- 

 tensity) is in the perpendicular plane, there is nothing to 

 compensate the action of each magnet on the other. The 

 best thing that can be done in this case, is to determine the 

 position of the second magnet in such a manner, that the 

 direction of its action on the first shall coincide with the 

 magnetic meridian* In such case, the position of the first 



