444 , TRANSACTIONS OP SECTION E. 



2. Colour in the Representation of Hill Features. By A. R. Hinks, M.A. 



3. Mean Sea-level. By Captain E. 0. Henrici, R.E. 



In the report of the Royal Commission on Coast Erosion it is stated that 

 there is some evidence that the land on the coasts of Northumberland and 

 Durham is sinking relatively to the sea. The only method of determining 

 whether this is so or not is by means of accurate observations of mean sea-level 

 with reference to marks on shore. The sea-level is, however, constantly alter- 

 ing, not only with the tides but also with the winds, height of barometer, and 

 rainfall. Accordingly, in order to determine what is mean sea-level it is neces- 

 sary to take observations over a long period of years. Observations at some 

 two dozen stations round the coasts of Great Britain were taken by the 

 Ordnance Survey in 1859, but they were carried out over much too short a period 

 to enable any conclusions to be drawn as to earth movements. There exist some 

 fifteen recording tide-gauges round the coasts of Great Britain, but as they 

 are installed to obtain tidal records for navigation purposes no great degree 

 of accuracy is required, and it is probable that the work of reducing their 

 records to mean sea-level would not be justified by results. 



The determination of the relative value of the height of mean sea-level as 

 determined by levelling between the different gauges was carried out in 1860, 

 but it is possible that there may be an error of a foot in the determination of 

 the height of the zero of a tide-gauge as compared with Ordnance datum, and 

 there may also be an error of a foot in the determinations made by the Ordnance 

 Survey of the height of mean sea-level as compared with the zero of the tide- 

 gauge. The values of the height of mean sea-level above or below Ordnance 

 datum varied from to nearly 2 feet, with an average of 0-65 foot above. These 

 variations are about what is to be expected from errors of observation, and do 

 not afford any evidence that mean sea-level is not constant round our coasts. 



4. The Height of Ruwenzori. By Captain E. 0. Henrici, R.E. 



It was mentioned in the report of the Committee on the Geodetic Arc in 

 Africa, presented last year at Sheffield, 1 that observations were taken by Captain 

 Jack, R.E., in the course of the geodetic work, to determine the height of 

 Ruwenzori. The computations were not completed by the time Captain Jack 

 had to leave England, and the data were left in my hands. 



The initial mark, with reference to which the heights were determined, was 

 the station peg at Lake Albert Station. The heights of all the stations observed 

 in the arc triangulation were computed, and the probable errors of the results 

 rigidly determined. 



From three of these stations, viz., Omunturok, Oruha, and Kasunju, hori- 

 zontal angles were observed into the highest point of Ruwenzori. These agreed 

 well, giving the position of the highest point 0° 23' 10"690 N.lat., and 0° 49' 

 31"'949 long, west of Kicherere. 



This gives the position of the highest point of Ruwenzori : 0° 23' 10"'690 

 N. lat., 29° 52' 15" E. long. 



Vertical angles were observed from four stations, viz., Muruha, Kabuga, 

 Singirro, and Oruha, giving a mean value of 14,768T feet above Lake Albert 

 Station, with a probable error of Jh 2'1 feet. The mean probable error of the 

 stations from which observations were taken was i 1'3 foot. 



The coefficient of refraction was taken at 0-060, a figure arrived at after a 

 study of the values for the stations on the arc at which reciprocal observations 

 were taken. 



The height of Lake Albert Station was arrived at as follows : The mean 

 height of the station peg above the lake, May to July 1908, was 5'30 feet. The 

 mean reading on the tide gauge at Butiaba during the same period was 275 feet. 



The height of the zero of the tide gauge is given as 617'350 m. above mean 



1 Brit. Assoc. Reports, 1910, pp. 75-76. 



