Ixviii GENERAL SUMMARY OF SCIENTIFIC AND 



and independent of the direction, duration, or strength of the cur- 

 rent. 



Oberbeck has experimentally determined the resistance which the 

 air offers to an induction spark. He shows that it is a function of 

 the strength of the currents, and that hence its numerical value may 

 be calculated in the same way as that of solid or liquid conductors. 



Bauermann communicates a method of showing the conductivity 

 of the various forms of carbon, due to Dr. Von Kobell, of Munich, 

 A fragment of the carbon to be tested is lield in a pair of zinc tongs 

 (a simple strip bent on itself) and immersed in copper sulphate solu- 

 tion. The proportion of coj^per deposited on the carbon indicates 

 its conducting power. 



Lippman notes the curious experiment of putting a mass of water 

 contained in a glass vessel in communication with the earth, and 

 then bringing near it an excited rod of resin ; oxygen is evolved at 

 the wire. On removing it the hydrogen is disengaged. But before 

 removing the rod, where was the hydrogen ? The author says it is 

 neither in combination nor solution, but is retained upon the surface 

 of the water. 



Buff has made an extended investigation into the changes of 

 temperature which are produced when an electric current passes 

 from one metal to another. The evolution of heat is proportional to 

 the quantity of electricity passing in a unit of time multiplied by 

 the electro-motive force of the battery. 



Lovering has proposed an ingenious method of determining the 

 velocity of electricity by means of two electro-magnetic forks vibrat- 

 ing at right angles and giving Lissajous' curves. If known resist- 

 ances be introduced in the circuit of one of the forks, the change in 

 phase will indicate the retardation of the current and give the data 

 for the calculation. 



Deprez has contrived a new form of electro-magnetic register for 

 recording velocities. With the apparatus figured, which is simple 

 in its construction, 600 complete signals can be recorded in a 

 second. 



Bichat has published an interesting memoir upon induction, in 

 wliich he shows that as a current of high electro-motive force may 

 be developed from one of low by means of the so-called induction 

 coil, so, by passing a current of high tension from a Holtz machine 

 through the outer coil, a current is generated in the inner coil capa- 

 ble of producing magnetic effects and of decomj^osing water, pre- 

 cisely as does the direct current from a battery. He also suggests 

 an important modification in the Foucault interrujDter, by which the 

 intermittent current is interrupted more uniformlj' . 



"Weber has communicated an extended paper on the theory of the 

 galvanometer, in which he discusses tlie whole subject mathemat- 

 ically. 



