Itk) NOTICES OF LECTURES. 



on the other hand, they were confined in perpetual darkness, they 

 would become enfeebled, and their tissue so lengthened, that none of 

 the parts would acquire solidity and vigour, and finally perish ; this 

 is owing to the inability of plants to decompose carbonic acid gas 

 in the dark, for a specimen of which the reader has only to refer to 

 the remains of the winter's stock of potatoes, in spring. 



Thus we see that plants grow chiefly by day. Mayer found the 

 stem of a Belladonna Lily, and plants of wheat and barley grow nearly 

 twice as fast by day as at night ; and Mulder states that he has arrived 

 at a similar result in watching the development of other plants. 



In my next I purpose to notice the crocus and snow-drop. 



J. H. G. 



LITERARY AND PHILOSOPHICAL SOCIETY. 



December 12. — The Eev. Newman Hall, BA. delivered a lecture "On tlie 

 Theory of Sensation." The lecture commenced with a definition of sensation, 

 which Mr. Hall regarded as a general expression indicative of those states of the 

 mind, which immediately follow an affection of the organs of sensation, on being 

 acted upon by external objects. The theory of sensation, he understood to be an 

 explanation of the mode in which external objects produce those mental states. 

 Matter is a substance altogether distinct from mind, and possesses entirely different 

 qualities. Connected with our material organization there is the sensorial organ, 

 consisting of the brain, the spinal marrow, and the nerves, the external terminations 

 t)f which, or the organs of sense, are in some manner affected by other material sub- 

 stances, external to the body. These affections of the organs of sense are the phy- 

 sical causes, and the immediate precursors of our mental sensations. Thus external 

 objects affect the immaterial mind through the medium of the bodily organs. The 

 question arises, how is this effect produced ? Having noticed the several theories 

 both ancient and modem, by which this phenomenon has been attempted to be 

 explained, and pointing out the various errors of those theories, Mr. H. proceeded 

 to state the theory generally adopted in the present day, viz. — " That external 

 objects, by the medium of light and air, or by apparent contact, produce some change 

 in the organs of sense, the nature of which change is unknown : that this impres- 

 sion is conveyed along the nerves in some manner unknown, and that the mental 

 state called sensation immediately results in some method also unknown." Modest, 

 however, as this theory was, it probably pretended to too much knowledge ; the pro- 

 cess of sensation was, perhaps, more simple than this theory represented. Why 

 may not the mind become conscious of the change produced on the organ of sense 

 immediately on that change taking place, without the transmission to the brain. 

 Mr. Hall proceeded to adduce arguments in support of this opinion, which he con- 

 tended appeared to be the most philosophical, and did not pretend to an assumption 



