471 



of voltaic elements formed of an amalgam of potassium with zinc, 

 copper and platina, a solution of a salt of the negative metal being 

 the interposed liquid, are given ; the last combination is one of great 

 electromotive energy, and when a voltameter is interposed in the 

 circuit, it decomposes abundantly the water contained in it. A still 

 more energetic electromotive force is exhibited by a voltaic element, 

 consisting of amalgam of potassium, sulphuric acid, and peroxide of 

 lead. The author then shows, that if three metals be taken in their 

 electromotive order, the electromotive force of a voltaic combina- 

 tion formed of the two extreme metals is equal to the sum of the 

 electromotive forces of the two elements formed of the adjacent 

 metals. 



Among the instruments and processes described in the subsequent 

 part of the memoir are the following. 1. An instrument for mea- 

 suring the resistance of liquids, by which the errors in all previous 

 experiments are eliminated, particularly those resulting from neglect- 

 ing the contrary electromotive force arising from the decomposition 

 of the liquid. 2. The differential resistance measurer, by means of 

 which the resistances of bodies may be measured in the most accu- 

 rate manner, however the current employed may vary in its energy. 

 3. An instrument for ascertaining readily what degree of the gal- 

 vanometric scale corresponds to half the intensity indicated by any 

 other given degree. 4. A means of employing the same delicate 

 galvanometer to measure currents of every degree of energy, and 

 in all kinds of circuits. 5. Processes to determine the deviations of 

 the needle of a galvanometer corresponding to the degrees of force, 

 and the converse. 



4. " On the Organ of Hearing in Crustacea." By Arthur Farre, 

 M.D., F.R.S. 



The author finds that in the Lobster (Astacus mariniis), the organ 

 of hearing consists of a ti*ansparent and delicate vestibular sac, which 

 is contained in the base, or first joint of the small antennae ; its situa- 

 tion being indicated externally by a slight dilatation of the joint at this 

 part, and also by the presence of a membrane covering an oval aper- 

 ture, which is the fenestra ovalis. The inner surface of the sac gives 

 origin to a number of hollow processes, which are covered with 

 minute hairs and filled with granular matter, apparently nervous. 

 A delicate plexus of nerves, formed by the acoustic nerve, which is 

 a separate branch supplied from the supra-oesophageal ganglion, is 

 distributed over the base of these processes and around the sac. 

 Within the sac there are always found a number of particles of sili- 

 ceous sand, which are admitted, together with a portion of the sur- 

 rounding water, through a valvular orifice at the mouth of the sac, 

 being there placed apparently for the express purpose of regulating 

 the size of the grains. The author considers these siliceous parti- 

 cles as performing the office of otolites, in the same way as the 

 stones taken into the stomachs of granivorous birds supply the office 

 of gastric teeth. Several modifications of this structure exhibited 

 in the organs of hearing of the Astacus Jiuviatilis, Pagurus streh- 



B 



