METEOROLOGICAL CONDITIONS 79 



large numbers at low elevations. By degrees the migration passes 

 into higher altitudes, its speed being at the same time strikingly 

 accelerated. The number of birds which alight during the morning 

 hours is at that time considerably diminished, and the few birds 

 that do so, soon start afresh on their journey, so that by the time 

 that the wind has completely changed to the west and rain has 

 begun to fall, not another bird is to be seen. Migration phenomena 

 of this kind have been frequently observed ; among other instances, 

 in October 1882. From the first week of that month up to the 

 22nd the prevailing winds were south-east ; these on frequent 

 occasions rose to a great strength, being in such cases accompanied 

 by low, loose, swiftly-flying clouds. During all this time a powerful 

 mass-migration, or so-called ' rush,' was in progress, and the call- 

 notes of numerous migrants were heard during the night, and the 

 birds themselves were seen daily, particularly during the early 

 hours of the morning and forenoon, speeding across the island at 

 a great height ; but only very few of them were noticed to alight. 



During this time the cloud-formations at intermediate heights 

 in the atmosphere were moving from south-south-east and south ; 

 but at a very great altitude the air unfortunately was clear, though 

 undoubtedly there too the air-currents were moving in at least a 

 south-westerly direction ; such, at any rate, was still the case on the 

 evening of the 21st. Early on the 22nd a few loose isolated clouds, 

 not of the cirrus type, were already moving rapidly at a great height 

 from west-south-west, while the loose vaporous clouds below them 

 were still being driven along before a very strong south-east wind. 

 At the same time the Marine Observatory registered, as a storm 

 warning, a deep depression west of the Hebrides. During the fore- 

 noon of that day a very powerful and extremely rapid migration was 

 still in progress, the birds, so to speak, dashing across the island 

 without one of them alighting thereon. At noon the migration 

 completely ceased. Amid a powerful downpour of rain the wind, 

 which had increased considerably in force, veered round to the 

 west, and at midnight blew with great violence from the south-west 

 and west, accompanied during the night by heavy sheet-lightning. 

 On the 23rd stormy winds, accompanied by heavy rain-clouds, 

 continued blowing from the west, and there was no longer a bird 

 to be seen. 



The birds, which travelled past and across the island in such 

 vast masses and in such unusual haste during the last part of this 

 period, had, as might be gathered from the movement of the 

 elevated cloud-strata, been driven out of their normal migration 

 tracks by contrary west winds. In consequence of these winds 

 reaching the surface of the ground, the migration, which had been 



