22 UNCERTAINTY OF MODERN METEOROLOGY. 



gauge above tlie earth i's a point of much consequence in making 

 estimates from its measurements.* The data from which results 



* Careful observations by the late lamented Dallas Bache appeared to show 

 that there is no such difference in the quantity of precipitation falling at 

 slightly different levels as has been generally supposed. The apparent differ- 

 ence was ascribed by Prof. Bache to the irregular distribution of the drops of 

 rain and flakes of snow, exposed, as they are, to local disturbances by the cur- 

 rents of air around the corners of buildings or other accidents of the surface. 



Mr. Bache's conclusions seem not to be accepted by some experimenters in 

 England (see Quarterly Journal of Science for January, 1871, p. 123), but ac- 

 cording to Greaves, President of the Meteorological Society (see Academy, 

 7th Dec, 1878, p. 547), the difference above alluded to is now generally ac- 

 knowledged to be almost entirely due to the action of wind. The periodical 

 Nature of Sept. 22, 1881, p. 495, also contains an article on Prof. Phillips's 

 observations of the rain-fall at Yorkminster, which appears to confirm this 

 theory. The general conclusion of the article is in favor of Prof. Jevons's 

 views, announced in 1861, namely : that the phenomena observed were all 

 consistent with the supposition that the fall of rain was practically identical 

 at all elevations, the observed differences being due to imperfect collection by 

 the gauges. Prof. Jevons's theory is now almost universally adopted, and it 

 shows the importance of great care in the selection of positions for rain- 

 gauges ; but in this theory he refers merely to the height of the gauge above 

 the ground, and takes no notice of the remarkable difference of rain-fall ob- 

 served at stations at very small distances from each other. 



Thus, by the Report of Dr. B. A. Gould, Director of the Observatory at 

 Cordova, in the Argentine Confederation, it appears that at the house of the 

 secretary, which is one mile distant from the Observatory, and 36.6 metres 

 lower, during a period not given, but apparently of some months, a pluviom- 

 eter, three and a half metres above the ground, showed a precipitation of 496.5 

 millimetres. The measured fall at the Observatory during the same period 

 was 459.1 millimetres, showing a difference of eight per cent, in favor of the 

 lower station. 



In a period of some weeks, a rain-gauge on the roof of a house near the 

 Observatory, 4.02 metres above the standard instrument at the Observatory, 

 registered 137.04 millimetres, the standard pluviometer 150 millimetres, a dif- 

 ference of eight per cent, in favor of the lower station. 



The island of Mauritius, lying in the Indian Ocean in about 20° N. L., is 

 less than forty miles long by about thirty in breadth. Its surface is very 

 irregular, and though it consists, to a considerable extent, of a plateau from 

 1,200 to 1,500 feet high, there are three mountain peaks ranging from 2,300 

 to 2,700 feet in height. Hence, though the general climatic influences are 

 everywhere substantially the same, there is room for a great variety of expos- 

 ures and of other purely local conditions. It is said that the difference of 

 temperature between the highest and lowest stations does not exceed eight 

 degrees F. , while, according to observations at thirty -five stations, the rain-fall 

 in 1872 varied from thirty-three inches at Gros Cailloux to one hundred and 



