On Atmospheric Influence of Heated Terrestrial Surfaces. 531 



The author observes that if rarefactions alone produce sound, it 

 follows that a simple contraction of the muscles of the ear will ren- 

 der sounds inaudible. It follows also, on the same hypothesis, that 

 a more delicate exercise of the same muscles will render the organ 

 minutely susceptible to the influence of certain sounds, to the exclu- 

 sion of others. It is urged also, that, admitting the action of these 

 muscles to be to a large extent involuntary, there can be no doubt 

 that by practice a great degree of command may be acquired over 

 them. The author conceives that we may in this way account for 

 the facility acquired by many persons of reading and writing, and of 

 carrying on intricate trains of thought, without being disturbed by, 

 or being conscious of, the noises around them. He conceives also 

 that the same mode of explanation may be applied to account for the 

 power of appreciating and analysing the most complex harmonies 

 possessed by persons having a fine musical ear ; which the author 

 considers to be as certainly the result of specific mental and muscular 

 training, as the faculty of vocalization, or the art of playing on a 

 keyed instrument. 



The author concludes by observing that the equations for the 

 transmission of an undulation along a musical string require a similar 

 correction to that introduced in the case of aerial vibrations. The 

 discussion of this branch of the subject he reserves for a future op- 

 portunity. 



May 6. — The Lord Wrottesley, President, in the Chair. 



The following communications were read : — 



" On the Influence of Heated Terrestrial Surfaces in disturbing 

 the Atmosphere." By Thomas Hopkins, Esq. 



In this paper the author stated that the Hadleian theory of winds, 

 which is now the one generally recognized, is not supported by the 

 evidence of facts, but rests on assumptions founded on imaginary 

 effects of the partial expansion of the atmospheric gases by heat. It 

 is assumed in that theory, that when the tropical heat expands these 

 gases, they rise and flow away laterally in the higher regions towards 

 the poles, from which they return to the tropics in the lower regions. 

 But it was contended by the writer of the paper, that such heating 

 of the gases merely expands them, without making them rise and 

 overflow to other parts. The theory of Halley, once generally adopted, 

 represented that the air was greatly heated in the particular part 

 where the sun was nearly vertical, which made the air rise in that 

 part alone, admitting cooler air to flow into the place of that which 

 had ascended, and produced an influx of cool air below, from all parts 

 around, to the heated part, and an overflow above from it. But in 

 time experience showed that this hypothesis was not in accordance 

 with facts, and it was abandoned. The theory of Iladlcy, which 

 has been since adopted, substitutes the whole tropical belt, for the 

 heated locality of Halley, which travelled with the sun in his daily 

 course ; but the supposed rise of air in the tro|)ical belt, with an 

 overflow above and an influx below, was assorted to be e(|naily un- 

 supported by experience, and, being unproved, may be fallacious, 

 2 M 3 



