164 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



known. In fact, the electro-motive force, at the separating 

 surface of the metal and the fluid, varies according to the 

 time that they have been in contact with each other. This 

 variation of the electro-motive force is, in many cases, purely 

 a secondary phenomenon, in that by chemical means a foreign 

 substance is formed between the metal and the fluid, which 

 greatly changes the separating surface, and gives rise to a 

 chemical polarization. Electric currents are also, in these 

 cases, due to the accidental formation of foreign substances, 

 and to the exposure ot the metal to the atmosphere, or to 

 contact with the fingers. But even when foreign substances 

 and chemical influences are excluded in the most perfect man- 

 ner possible, as, for example, when platinum or gold, is dipped 

 in water, movements of the needle are still visible ; and it 

 has been suspected that the air which is retained in contact 

 with the surface of the metal, or perhaps the method that 

 has been employed to cleanse the platinum or gold may have 

 had an important influence in bringing about an electric cur- 

 rent. Quincke has recently subjected this phenomenon to 

 careful investigation, and has observed that the strength of 

 the electric current increases with the increasinc: resistance 

 of the column of fluid between the electrodes ; that it in- 

 creases with the decreasino; strengjth of the concentration of 

 the salt solution that may be employed ; that it has no rela- 

 tion to the capillary constants of the fluids employed, and 

 that it originates probably in the change in the molecular 

 condition of those portions of the fluids which are in the 

 neighborhood of the metallic surfaces. 19 C, VIII., 71. 



PEIORITY OF DISCOVERY OF THE PRINCIPLE OF THE 



GRAMME MACHINE. 



According to a recent lecture of Dr. Andrews, the celebra- 

 ted magneto-electric machine of Gramme, which is the only 

 one that gives a continuous electric current, was preceded 

 by the publication in 1865, by Dr. Pacinotti, of Florence, of 

 a machine for a similar purpose, whose essential feature was 

 in the novel form of the armature, by means of which contin- 

 uous electrical currents, always in the same direction, could 

 be obtained from a magnet. Pacinotti does not indeed ap- 

 pear to have constructed the machine described by himself, 

 but states that he verified the correctness of his views, and 



