Mr. R. Patterson on the appearance of Clouds of Diptera. 7 



culiar and not unmelodious humming noise, like the distant 

 sound of the machinery of a spinning-mill, but more varied. 



The columns rose perpendicularly to the height of from 30 

 to 60 feet, and in some instances to the height of 80 feet. 

 They were equally abundant over trees of every kind, as ash, 

 beech, birch, poplar, &c, and so numerous were these distinct 

 columns, that so many as from 200 to 300 were visible at the 

 same time. As each column was every instant undergoing a 

 change in density of colour, diameter, elevation or form, the 

 phenomenon was one of exceeding interest, especially as con- 

 nected with the living myriads, which in these aerial gambols 

 gave expression to their enjoyment. 



Some individuals were taken in a gauze net, and on exami- 

 nation by Mr. Haliday proved to be Erioptera trivialis $ 

 (Hoffmansegg) ; others taken two evenings afterwards at the 

 Royal Academical Institution (where they presented the same 

 appearance, but in smaller masses) were Chironomus testaceus* 

 (Macquart) ; so that different species would appear to have 

 occasioned a similar phenomenon in different localities. 



As we are at present ignorant of the conditions which are 

 requisite to call these tiny multitudes into existence, the state 

 of the barometer and thermometer for some successive days 

 is given as recorded by Mr. Bryce : — 



Thermometer. Barometer. 

 Mean of 9 a.m. and 2 p.m. Mean of 9 a.m. and 3 p.m. 

 June 9 69*125 30*398 



— 10 69-25 30-332 



— 11 69-50 30-400 



— 12 73-75 30-450 



— 13 6962 30-378 



During all these days there was a very light summer wind 

 between E. and N. On the 13th, between two and six p.m., a 

 thunder-storm with rain passed north by west over Lough 

 Neagh, Antrim, &c, and was followed by a diminished tem- 

 perature. 



I have been unable to define the precise range in which 

 these singular assemblages of insects appeared. About Bel- 

 fast they were everywhere abundant over trees. At the re- 

 sidence of one gentleman, about a mile to the north of the 

 town, they came forth in myriads ; and when the noise of 

 their wings first attracted his attention, he for a moment 

 supposed it to be the sound produced by letting off the 

 steam from a steam-vessel at a distance. By a lady on the 



* In the box sent to Mr. Haliday, containing probably above 100 speci- 

 mens of this insect, there was but one female. 



