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 0 is the mean vapour tension at the two stations, and ij the 
1 — 0,378 0 
V 
mean 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 Bnjongolo and the 
observed 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 normce. 
Regarding the results obtained, 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 influence of such a correction, reference may 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 0, 1 Celsius (41° F.), 
hence the mean pressure was about 451 mm. and the mean temperature 0°*9 Celsius (33° F.). 
Had the air been saturated at this temperature the vapour tension would have been 4*87 mm. 
Admitting a humidity of CO the tension falls to 2*92 mm., with which datum, and with the 
mean pressure of 451, we get the cologarithm of the term of correction for the humidity, 
namely: 
colog.- = 0*00103 
1 —0*378— 
V 
Without taking account of the humidity, the height of Margherita Peak above Bujongolo 
was found to be 1,32.4 metres; with this added it becomes 1,327 metres, that is to say, we 
have a rise of about 0*22 per cent. Admitting a humidity of 80 the height would become 
1,328*5 metres, with a rise of 0*33 per cent. 
367 
