390 Eoj/al Institution of Great Britaitt. 



direction or the other, according to particular circumstances ; and 

 also the probable explanation which such phaenomena afforded of the 

 absorption of fluids by plants, and the ascent of the sap in their 

 vessels. It is a fact discovered by M. Dutrochet, that if part of the 

 caecum of a chicken be tied into a bag, and then attached to the end 

 of a tube, if the bag and a little of the tube be filled with a solution 

 of gum, sugar, or several other substances ; and if being so filled, 

 the bag be immersed in water, the water will pass from the out- 

 side to the inside, will increase the quantity of fluid there, and will 

 raise its level much above the level of the water without. This de- 

 termination of the fluid from without inwards is called Endosmose. 

 Some substances cause a contrary current, and then the term Exos- 

 mose is applied. The effects produced by various substances and in 

 various ways were illustrated experimentally at the lectHre-table. 

 M. Dutrochet refers this influence altogether to electricity, and con- 

 siders it as a principal power in causing the ascent of sap in plants. He 

 admits only another, which is supposed to reside in the leaves at the 

 upper ends of the vessels, and which may be assimilated to the action 

 of an air-pump. In pointing out the extent and influence of these phae- 

 nomena in nature, Mr. Burnett stated his opinion, that though power- 

 fully influential in causing the entrance of water into the plant, yet 

 Endosmose was not by itself, or in conjunction with the action of the 

 leaves, suflicient to explain the phaenomena of ascent in the vessels ; 

 and he described several experiments in which the influence of both 

 powers being removed, still the ascent took place. Thus, when the 

 root and the leaf were removed from a celery stalk, and the latter 

 immersed in a coloured solution, the solution still ascended the vessels 

 of the plant. Again, when roots were put into strong.solutions of 

 gum and sugar, such as, with reference to the quality of the sap in the 

 vessels, should have caused the Exosmose or passage of the fluid out 

 of the vessels, still the natural effect was undisturbed. 



April 3rd. — On this evening Mr. Faraday, in Mr. Wheatstone's 

 name, concluded the series of experimental investigations and illus- 

 trations which have been brought forward on former occasions in the 

 theatre of the Institution, On the Resonance, or reciprocated Vibra- 

 tions of Volumes of Air. The details this evening related principally 

 to the effects produced by the reciprocated vibrations of the volumes 

 of air in the mouth and the cavities of the ears, when they are nearly 

 or altogether closed. The important influence of multiple reciprocated 

 vibrations in aft'ecting the quality of a sound supposed to be simple, 

 but in reality consisting of several simultaneous accordant sounds, 

 was stated, and exemplified by experiment. 



When illustrating the curious effects produced by closing the 

 cavities of the ears, and causing the volumes of air so insulated to re- 

 ciprocate to the vibrations communicated through their side, amongst 

 other things the Microphone of Mr. Wheatstone was described and 

 shown, and its use in detecting the vibrating condition of any part of 

 a sounding body, as a plate, or the sound-board of an instrument, or 

 even the locality of a loose screw in a machine, fully demonstrated. 



During the evening a striking illustration was given of the possi- 

 bility 



