I.—REPORT ON ASTRONOMIC OBSERVATIONS. 
By P. Campigli. 
The astronomic determinations made by H.R.H. the Duke of the Abruzzi 
on the route between Entebbe and Ruwenzori are the result of solar 
observations made with an aluminium sextant, which was constructed in the 
engineering' workshop of the Naval Hydrographic Institute at Genoa. Its 
graduated arc has a radius of 145 mm. (about 6 inches), being so subdivided 
as to show the 20 seconds on the vernier. Magnaghi’s astronomic circle was used 
only in the very few cases where, for observations at the meridian or in its 
neighbourhood, the height of the sun was such as to make the use of the 
sextant less convenient. 
Of course, all measured heights were duplicated at an artificial mercurial 
horizon, care being taken to reverse the position of the roof at half of each 
series of observations, in order to lessen to the utmost the influence of errors 
in case the glasses of the said roof should eventually become prismatic-ally 
affected. 
The calculations were carried out by means of logarithms of 8 decimals, 
tables of 7 decimals being used only in calculating the mean hour at Greenwich 
at the moment of emersion of BAG 81 from the lunar disk, as observed at 
midnight between the 11th and 12th July, 1906, at Bujongolo, the last 
astronomic station in the district nearest to the Ruwenzori uplands. 
The astronomic refraction r, corresponding to the considerable altitudes at 
which the astronomic observations were made during the journey, was calculated 
with Bessel’s well-known formula:— 
r = log (a tang z) + A (log B + log T) + log y, 
neglecting the factor A, for apparent zenith distances z, under 11°, and the 
factor A, besides A, for apparent zenith distances less than 45°. The values of 
the elements contained in the foregoing formula were deduced from Albrecht’s 
tables, 1894 edition. But the Table 34/, which gives the value of log B, only 
comprises barometric pressures between 600 and 780 mm. (24 and 31 inches), 
x 2 
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