198 



lions, a transit instrument by Dollond was used, which was 10 feet 

 in focal length, and 4-75 inches aperture. For observing the comet, 

 an eye-glass magnifying 86 times was employed. 



A paper was then read, entitled, "On the supposed Powers of Suc- 

 tion of the Common Leech." By Thomas Andrew Knight, Esq., 

 F.R.S., President of the Horticultural Society. 



From observing the feebleness of the muscular force exhibited by 

 the leech in its progressive movements through the water, the author 

 was led to doubt its possessing the powers of suction that are so uni- 

 versally ascribed to it. A fact which came under his notice above 

 sixty years ago, of considerable loss of blood from the leg following 

 the bite of a vigorous leech, suggested to him the idea that the animal 

 might become rilled with blood simply by the injection of its body? in 

 consequence of the impetus with which the blood is made to flow into 

 it from the part bitten ; — an impetus which he imagines may be oc- 

 casioned by the introduction of a peculiar kind of venom. He con- 

 siders the irritation which often accompanies the bite of a leech as 

 corroborating this hypothesis : he admits, however, that the inflam- 

 mation excited by the sting of a bee or a wasp is attended with effects 

 of a totally opposite kind - } for, in that case, the blood, instead of 

 having a tendency to flow, stagnates around the point where the 

 poison has been instilled. 



A paper was also read, entitled, " Experimental Researches in 

 Electricity.— Fourth Series." By Michael Faraday, Esq., D.C.L., 

 F.R.S., Fullerian Professor of Chemistry in the Royal Institution of 

 Great Britain. 



The author, while prosecuting his researches on electro-chemical 

 decomposition, observed some phenomena which appeared to be refer- 

 able to a general law of electric conduction not hitherto recognised. 

 He found that an electric current from a voltaic battery, which is 

 readily conducted by water, did not pass through ice : even the 

 thinnest film of ice, interposed in the circuit, was sufficient to inter- 

 cept all electric influence of such low intensities as that produced by 

 the voltaic apparatus, although it allows of the transmission of elec- 

 tricity of such high intensity as that excited by the common electrical 

 machine. The author ascertained that a great number of other sub- 

 stances, which are solid at ordinary temperatures, do not conduct the 

 electric current from the voltaic battery until they are liquefied. 

 Among these are potassa, protoxide of lead, glass of antimony, and 

 oxide of bismuth ; various chlorides, iodides, and sulphurets ; and 

 also many of the ordinary neutral salts with alkaline bases. In almost 

 every instance the bodies subjected to this law are decomposable by 

 electricity ; and their decomposition can be effected only when they 

 are in a fluid state, and while they are conductors of electricity. The 

 author inquires how far these two properties are connected together, 

 or dependent the one upon the other ; but finds that several excep- 

 tions occur to any general proposition that he attempted to establish 

 on this subject. 



