76 THE FKESH-WATER LOCHS OF SCOTLAND 
The Glen Ogle Storm. — One more instance of the connection 
between abrupt barometric and seiche disturbances may be given, as 
it was one of the most remarkable observations made on Loch Earn. 
On 2t3rd August, after a dead calm during the night and heavy 
rain in the early morning, at 8*^ 20™ there was a light breeze, W., 5 
(mile/hour). There was low cumulus on the hills to E. and N.E., but 
there was bright sunshine, and the clouds (3) in general were high. 
The main drift was from S.E., but there was a mackerel formation 
apparently moving in a different direction ; also a mare's-tail showed 
to S.W. 
The waves were running from W. — a slight swell, diversified by 
oil bands, which were seen at intervals throughout the day. 
From 8^^ 20"^ to 12'^ 30'" the wind was light, fluctuating with a 
rough period of l'\ At 12'' 30™ there was a sudden gust of 15 
(mile/hour). After that the wind rose somewhat, and fluctuated for 
about 5 hours between 0 and 13 (mile/hour) mean velocity. It was 
unusually gusty, and at 14^' 5™ an extreme velocity of 25 (mile/hour) 
was registered. At this moment a black rain-cloud came down Glen 
Ogle, and reached over the western part of the lake as far as 
Ardvoirlich, where it stopped. 
At 14'' 50™ there came on a sudden rain-shower, the wind being 
then W. by S. After this there was rain at intervals till 20^ 18™, an 
especially heavy shower at 17'^ 20™. 
At 20^ 18™ the wind was W.S.W. and variable. 
At 14'' 7'" a microbaric disturbance passed Ardtrostan, travelling 
with a velocity of 15 (mile/hour) from W. 60° N. (36 along the lake). 
One of the Lake Survey staff* was looking at the uninodal limno- 
graph, and saw it record the sharp depression shown in fig. 28, just 
as the squall came up. For some time before, the limnographs at 
the uninode, binode, and Picnic Point had been drawing almost 
straight lines. The seiche weather had, in fact, been the calmest 
known in the two months of observation. 
The maximum depression (4 mm.) at the uninode and the 
maximum elevation (5 mm.) at the binode were nearly simultaneous, 
the latter apparently following about IJ™ after the former. Un- 
fortunately, owing to the irregularity of the clock at the uninode, 
certainty on this point is not attainable. 
It seems clear that an abrupt elevation of the surface travelled 
along the eastern part of the lake. The first rise began at the binode 
at 13'^ 55-31™, and at Picnic Point at 14^ 5*24™, that is, 9 93™ later. 
The first maximum (5 mm.) is seen at the binode at 14'^ 1*05'", and 
at Picnic Point at 14'^ 10*57™, that is, 9*52™ later. The velocity of 
propagation of the first rise would thus be 6*0 (mile/hour), and of the 
first maximum 6*3 (mile/hour), and it is interesting to notice that 
