ELECERIC LHECEN TRICILLES: 279 
It may easily be imagined that some compensatory phenomena transpire to 
prevent the very destructive winds which this implies; perhaps by ofposzng pres- 
sure, as, in mechanics, the exhaust of a low pressure engine is made to add to 
its working force. The means of determining vapor tension by the hygrometer 
are imperfect ; but if it is this influence which affects the barometer it shows why 
local observations are so unreliable, for after all, to one dependent upon his own 
weather-glass, the following are about all the rules that have been given to guide 
him. 
1. If, after a continuance of dry weather, the barometer begins to fall 
slowly and steadily, rain will ensue; but if the fine weather has been of long dur- 
ation, the mercury may fall for two or three days before any preceptible change 
takes place, and the more time that elapses before the rain comes the longer the 
wet weather is likely to last. 
2. Conversely with regard to a rising barometer and fair weather. 
3. If the change ensues immediately it will not be permanent. 
4. If, though rising steadily for two days together or more, it rains, yet 
fine weather may be expected; though if it begin to fall upon its appearance, the 
fair weather will not be permanent, and conversely. 
5. Sudden falls of the mercury in spring or autumn, indicate wind; in the 
summer, during hot weather, a thunder storm; in winter, a change of wind with 
a thaw and rain, but in a continued frost, a rise indicates approaching snow. 
The difference in value of these indefinite rules to a system of actual meas- 
urement of atmospheric phenomena, embracing a large extent of the earth’s sur- 
face, can be readily perceived. Yet additional instruments are certainly desired ; 
self-registers, delicate and reliable, and with the barometer, an associated instru- 
ment to define these disturbing elements which compensate, disadvantageously 
for scientific purposes, the actual changes of pressure which we know are contin- 
ually taking place. 
ELECTRIC ECCENTRICITIES. 
Mr. James Johnstone sends to the Zdinburgh Daily Review the following in 
teresting account of the effects of a thunder-storm observed on the 7th ult. He 
says :—‘‘On the 7th ult., about 4:15 p. m. the lightning struck the craig which is 
named on the plan of Edinburgh ‘The Dasses,’ which overhangs the Hunter’s 
Bog on the east. The results are so extraordinary that they are worthy of notice 
in your columns. The rock struck is of the hardest basalt, commonly called 
_ whinstone, The lightning did not strike the sharp, serrated, front edge of the 
craig, as might have been expected; but, on the contrary, it struck the flat top 
covered with sod at a distance of three feet from the present edge, and that must 
have been between six and eight feet from the edge before the accident; for the 
lightning detached several tons of the rock from the front of the craig, and sent 
six large masses of rock down into the Hunter’s Bog. The largest of these meas- 
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