INTRODUCTION. XXIX 



whether or not the air blew in towards the centre, and that was, 

 that the trees, in the central line of the path, should be found ly- 

 ing parallel with the path ; and he stated that this had been found 

 to be the case in all the tornadoes which had been examined. 



To the third he answered, that if all the vapor should be con- 

 densed as Professor Forbes thinks, then the effects produced would 

 be much more violent. Professor Forbes would find, that if all 

 the vapor which is in a mass of air when the dew point is 73, 

 (and it is sometimes higher than that when tornadoes occur,) 

 should be condensed, the latent caloric given out would heat the 

 air more than 70 ; and in case of hail, nearly 80, by the addi- 

 tion of the caloric of fluidity. Professor Forbes would find, by a 

 rigid examination of the subject, that all the vapor is never con- 

 densed, because the dew point, at great heights, falls by expan- 

 sion faster than the temperature. 



As to the question whether Mr. Redfield and Colonel Reid's 

 theory of a whirl, or Mr. Espy's radial theory, was most accord- 

 ant with fact, Mr. Osier said, that from the investigation he had 

 given this subject, he was convinced that the centripetal action de- 

 scribed by Mr. Espy took place in most hurricanes. The particu- 

 lars, he, Mr. Osier, had collected, together with the indications 

 obtained from the anemometers at Birmingham and Plymouth, 

 satisfied him that the action of the great storm of the 6th and 7th 

 of January, 1839, was not rotatory at the surface of the earth 

 when it passed across England. He differed, however, both from 

 Mr. Espy and Mr. Redfield in one essential point, for he believed 

 it would be almost impossible to have a violent hurricane, without, 

 at the same time, having both rotatory and centripetal action. A 

 storm might very probably be generated in the first instance, in 

 the manner accounted for by Mr. Espy, or by the action of con- 

 trary currents ; in the first case, the rush of air towards a spot of 

 greater or less diameter, would not be perfectly uniform, owing to 

 the varying state of the surrounding atmosphere ; this, together 

 with the upward tendency of the current, would, in some cases, 

 produce a violent eddy or rotatory motion, and a whirlwind of a 

 diameter varying with the cause would ensue ; the centripetal ac- 

 tion would thus be immensely increased, the whirlwind itself de- 

 manding a vast supply of air, which would be constantly thrown 

 off spirally upwards, and diffused over the upper atmosphere, thus 

 causing the high state of the barometer which surrounds a storm. 

 He further stated, that he had brought his theory of the combined 

 action of centripetal and rotatory motion before the meeting of 

 this Association at Birmingham, and a short notice of it would 

 be found in the reports of the Sections. If no rotatory action 

 takes place, he believed that we merely experienced the rush of 

 air which necessarily precedes a heavy fall of rain or thunder 

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