III. — Meteorological, etc., Observations. 



found to a greater or less extent in the atmosphere. In the formula which 

 serves for the calculation of the altitudes {see p. 362) there occurs the factor 



where (b is the mean vapour tension at the two stations, and n the 

 1-0,378 



'/ 

 maan of the pressures, and this factor has reference to the influence exercised 



by the presence of the aqueous vapour on the readings of barometric altitudes. 



For Bujongolo the vapour tension is known, but not for the observed places 



on Ruwenzori, as here no psychrometric observations were made. 



The neglect of the factor relating to the humidity might be a cause of 

 error, to eliminate which, at least partly, a mean humidity of about 60 has been 

 admitted for the stratum of the air comprised between Bujongolo and the 

 o])served station.* 



This humidity of 60 is certainly less than the true mean, since at 

 Bujongolo the humidity is always very high (mean 89), and there is reason 

 to believe that it is always considerable in the other places too, where cloudy, 

 foggy and rainy weather prevail. 



On the Tables IX, X, XI and XII are recorded the altitudes of the various 

 other places on Ruwenzori, calculated with the previously indicated norma'. 



Regarding the results oljtained, it may be noticed that the determinations 

 made with the mercurial barometer were found to agree sufficiently well with 

 each other whenever it was possible to make more than one determination for 

 any given place, and they agree also with the surveys made with geodetic 

 methods. 



Owing to the irregular behaviour of the aneroid barometers, the measure- 

 ments taken with these instruments present a far less degree of approximation. 



* To show the possible inOuence of such a correction, reference uiav be made to the 



special case of the Margherita Peak. Here the pressure at 11 o'clock on 18th June was 



414'0 mm and the temperature — 3°3 Celsius (2G°'6 F.), whereas at Bujongolo, at 12 o'clock 



on the same day, the pressure was 487'9 mm. and the temperature 5°'l Celsius (41° F.), 



lience the mean pressure was about 451 mm. and the mean temperature 0°'9 Celsius (33° F.). 



Had tlie air been saturated at this temperature the vapour tension would liave been 4'87 mm. 



Admitting a humidity of 60 the tension falls to 2-92 mm., with which datum, and with the 



mean pressure of 451, we get tlie cologarithm of the term of correction for the liumidity, 



namely : 



polog 1 =0-00103 



1-0-378^ 

 n 



"Without taking account of the lunnidity, tlie height of Margherita Peak above Bujongolo 

 was found to be 1,324 metres ; witli this added it becomes 1,327 metres, that is to say, we 

 have a rise of about 0*22 per cent. Admitting a liumidity of 80 the height would become 

 1,328'5 metres, with a rise of 0'33 per cent. 



367 



