Chemistry and Physics. 513 
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The presence of moisture rendered the effect feeble and uncertain, 
probably owing to the deposit of a very slight film of moisture on 
the surface of the bar.—Phil. Mag., xlvii, 161. B OP. 
ll. Acoustic Transparency and Opacity of the Atmosphere.— 
Prof. Tyypax1, in a recent lecture at the Royal Institution, de- 
sounds were employed, large trumpets or horns sounded by steel 
reeds, whistles like those of alocomotive, and cannon. The observ- 
ers on board of a steamer moved to and fro until the limit of au- 
dibility was reached. The following are a portion of the results 
obtained, 
May 19th. Windstrong. At two miles the whistles became so 
wa 
that the rocks became 30° hotter than the surrounding grass, and 
hence formed the base of a column of hot air, from the surface of 
