247 
The author then alluded to the map of Egypt, which was 
made during the period it was under the dominion of the 
French republic, and which received from Buonaparte all 
that protection and assistance, which so much distinguished 
him on all occasions regarding the advancement of the works 
of science. This map was engraved on fifty-three sheets of 
copper, and the names are engraved both in Arabic and 
French. 
After this introductory account of the rise and present 
state of the topographical Art, Mr. Bald proceeded to the 
details connected with the survey of Mayo. 
The instruments used in this survey, were a seven-inch 
theodolite ; two five-inch theodolites, by Troughton; 4 
small theodolite, by Dollond ; and also a five-inch one by 
the same artist. In taking the levels over the bogs, two of 
Troughton’s best levels were used. The barometers were 
made by Mr. Thomas Jones, of London. There were also 
two plain tables, a chain for measuring base lines, a sextant 
four inches radius, and two sextants, each ten inches radius, 
divided to ten seconds for observing altitudes, one of which 
was made by Troughton. 
The proceedings of the geometrical details of the survey 
were then given, and the mode of describing the rise and 
fall of the ground, which was shaded on the map with 
a depth of colour corresponding to the sines of the angles of 
inclination. The irregularities of surface were simply de- 
lineated by hatching lines, drawn in the direction of the de- 
clivities, forming a series of normals, perpendicular to the 
horizontal lines of equal level. 
Dr. Smith read a paper (by Lieutenant Newenham, 
R.N.), “on a Tumulus or Barrow, near Rush, County of 
Dublin.” 
The barrow, called Knocklea, or the Giant’s Hill, is 
tuated on the edge of the cliff, about midway between the 
