230 Miscellaneeus Intelliyencc. 



inquires, whether it can be true that radiation of the electric currents 

 is subject to a law of interference, and acknowledges, notwithstand- 

 ing the alternations he has obtained, that new experiments are re- 

 quired. — Bib. Univ. xxxiii. 302. 



5. Earthy Bepositiona from Water influenced by the Electricity of 

 Metals in contact. — M. Dumas has noticed an interesting- case of 

 voltaic action, which has occurred with water contained in metaUic 

 tanks and tubes. The water from the springs in the neighbourhood 

 of the Seine are strongly charged with carbonate of lime, held in 

 solution by carbonic acid. When it is received and retained as be- 

 fore mentioned, it occasions incrustations, which, however, are not 

 indifferent as to the places on which they occur, but are governed 

 by the electrical relations of the metals forming the vessels. The 

 Sevres porcelain works are supplied with water of this kind, which is 

 received and retained in a leaden reservoir ; the general internal sur- 

 face of the lead presents scarcely a trace of deposit, but a thick coat 

 has been formed on the lines of solder by which the plates of lead are 

 joined. The incrustation is irregular, but evidently crystalline ; it 

 is slightly coloured by oxide of iron, and dissolves entirely, with 

 effervescence, in nitric acid. A bar of iron used to raise a valve, and 

 consequently plunged in the water, was covered with a layer five 

 or six lines in thickness, the lead in the immediate neighbourhood 

 being nearly free from the deposit. 



In the tubes which conduct the water, the deposit occurs only at 

 the soldered joints. The plumbers know this fact, and when the 

 pipes appear to be stopped up, always go to these places. The 

 copper cocks are also the localities of deposition. 



Abuiidant proof was obtained that these effects were, voltaic, by 

 immersing simple combinations of metals into portions of the water ; 

 and M. Dumas proposes a remedy for the evil occasioned by the 

 deposition, by causing it to take place in unimportant or acces- 

 sible situations. For this purpose he considers the assemblage of 

 tubes as an immense plate, and proposes to attach lateral tubes to it, 

 at intervals from twenty to thirty feet ; these are to be closed by 

 metallic plugs, containing rods affixed to them projecting into the 

 water, of such a nature as to become the negative part of the ar- 

 rangement ; all the depositions will then take place on these stop- 

 pers and rods, and none upon the lead. From the effects observed, 

 it is concluded that cast-iron will well answer the purpose. — Annates 

 de Chimie, xxxiii. 265. 



6. Instance of a returning Stroke by Lightning. — The returning 

 stroke of lightning is well known to be due to the restoration of the 

 natural electric state, after it has been disturbed by induction. 

 Thus if a person be brought into a highly electric and negative state 

 by induction, from the approximation of a body highly charged 

 positively, and then the latter be discharged by means having, no 

 connexion with the negatively electrified person, the negative state 



