= 
264 
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.” 
Itis 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 
