281 
side of the lake, from the action of a downward current at the 
opposite side. 
«‘ The fact that such a phenomenon has not been observed 
at Lough Neagh tends to confirm these views, for Lough 
Neagh is surrounded by flat shores, and is, therefore, not 
likely to be subjected to the action of vertical currents. 
«‘T remember seeing, somewhere in the writings of Hum- 
boldt, a conjecture that the tides in the Lake of Geneva, 
called seiches, arise from variations in the atmospheric pres- 
sure at different parts of the lake. ‘These variations are, no 
doubt, the results of such vertical currents, and suggest a 
mode of verifying the correctness of the views here put for- 
ward, if observers, furnished with barometers, resided on the 
opposite shores of a lake where the phenomenon has been no- 
ticed. I find that Saussure attaches great importance to the 
influence of vertical currents on the barometer. ‘This, he re- 
marks, is most likely to take place among the mountain gorges 
and funnel-shaped basins.* 
«« As the method of studying vertical currents by the 
variations of the barometer seems a little complicated, and too 
delicate for ordinary purposes, I have devised a wind-gauge 
which will indicate the existence of ascending or descending 
currents. It will also show the direction of the wind with 
regard to the points of the compass. Iam surprised at not 
having already heard of some similar instrument in the hands 
of those who have paid attention to mountain winds. The 
instrument I have devised is not a measurer, but simply an 
indicator, and I expect to receive one in a short time from our 
philosophical instrument-makers in Paris. 
‘“‘ Believe me to be, my dear Sir, 
“Yours very truly, 
‘¢ Henry HENNEsSY. 
“The Rev. T. R. Robinson, D. D.” 
* Voyages dans les Alpes, tom. iii., p. 71. 
2¥r2 
