Report on the Calculations of Heights from Observations made by By RICHARD These heights have been calculated from observations made with mercurial barometers of Captain George's pattern for travellers. The original observations are stated to have been corrected for instrumental errors. Where a number of observations have been made in the same month, the means of them have been used as the data for the upper station. The barometrical observations have been reduced to temperature 32°, by the table for graduations on glass scales, these barometers being divided on the tubes themselves. The air temperatures have been taken as correct. The following are the data used for the sea-level: the pressure having been obtained from Buchan's isobarometric charts, and the temperature from Dove's isothermal charts : Considering that the data for the sea-level must be subject to some uncertainty, it has not been deemed advisable to apply any correction for the diurnal range of the barometer. Hypsometrical observations have also been made with evident care. But, as the hypsometer can only be regarded as a substitute for the mercurial barometer-the calculation of heights from its indications depending upon the barometric formula-it should, when read with the barometer, be considered a check, and preference should be given to the barometer. Mercurial barometers are not liable to errors, which are of much importance in measuring elevations: on the contrary, hypsometers change their corrections by the rise of the zero point due to use and age, and a small unknown error causes a great difference in the heights. It would, therefore, be of little use to calculate these heights from the hypsometer's readings. The two series would merely serve to show by their differences that either the barometers or the hypsometers were not correct. These differences have been calculated by a shorter process, and it is interesting to notice how consistently they tell the same tale. They are as under : Error in heights due to H = 228 × 527 = 120 feet. The column H is the correction due to the hypsometers on the supposition that the barometers were accurate; B that due to the barometers taking the hypsometers as correct. The mean correction H shows that the hypsometers would have given heights on an average 120 feet lower than those deduced; the mean of B, that if the barometers are so incorrect the heights ought to be reduced by about 120 feet. However, it is scarcely possible for the barometers to have been incorrect to anything like this extent, while the correction for the hypsometers is not only possible but very probable. It would be interesting to have the instruments tested at the Kew Observatory. If this could be done, and the results should happen to support the inferences here made, it would afford a valuable confirmation of the theoretical accuracy of the Tables founded on the barometrical formula of Laplace, and the vapour tension formula of Regnault. It may be noticed that the corrections actually applied to the readings of the hypsometers average about + 0.2; and consequently the residual correction deduced now seems to show that their zeros have risen, so that now they are really more accurate than they were originally, the plus and minus corrections being almost nil. The comparisons instituted between the barometer and hypsometer observations afford a convincing proof of the fidelity with which the observations have been made. METEOROLOGICAL OBSERVATIONS taken on the WHITE NILE, between KHARTUM and RIGAF, 1874. By LIEUT. WATSON, R.E. Oct. 1834 28.60 28.60 28.55 75 72 83 74 71 71 74 70 78 71 80 74 80 75 28.64 28.61 28.58 83 76 86 76 77 79 75 86 76 79 28.67 28.61 28.60 79 75 87 77 78 75 28.62 28.60 28.55 82 76 83 76 76 77 74 80 75 78 76 77 87 85 70 78 74 77 77 73 77 79 74 75 78 87 77 80 78 79 80 73 79 71 73 75 71 74 73 74 75 75 71 76 : |