sing thl 



electricity 

 nts on the 

 of a con- 



' 



60 Scientific Intelligence. 



form around it a rising fringe. Moreover, when a flat piece of 

 iron is pressed into the ice, the fringe rising around it expands lat- 

 erally upon the borders of the piece, and tends thus, as in fluids, 

 to fill up the cavity made by the body driven in. These experi- 

 ments tend thus greatly to "illustrate the plasticity of ice; but it 

 would be very desirable that Mr. Bianconi if he continues his 

 researches, should accompany them by some measurements (as 

 has already been done by Mr. Heim), in order to obtain numeri- 

 cal values of the plasticity of ice under various circumstances.— 

 Nature, xv, 69; Jour, de Phys., v, 317. e. c. p. 



11. Velocity of Electricity.— -Dr. Sabine has devised a method 

 of measuring the contour of electric waves p 

 graph lines. It is probable that in this se 

 may be said to have a velocity. The early 

 time elapsing between starting "electricity hit 

 ductor and receiving it at the other end, ga- 

 tory results. This interval would depend on the electromotive 

 tone employed, the resistance and capacity of the conductor, and 

 the M-nsitn eness of the receiving instrument. It would therefore 

 by no means be proportionate to the length. By the following 

 method the electrical condition of any point of the line may be 

 examined quantitatively at intervals of -001 of a second or* less 

 ting the electric impulse. It thus becomes possible to 

 measure the form and speed of a wave. Suppose one end A of a 

 conductor A B is placed to earth, and that the other B is con- 

 nected with one pole of a battery whose second pole is put to 

 earth. Then any point of the conductor as C will assume a po- 

 tential which will be proportional to the resistance of A i '. This 

 potential may be measured by com jtant with I 



condenser or accumulator, and then discharging the latter through 

 a delicate galvanometer. When the circuit Is first closed a minute 

 interval of time is required before C will attain its full poten- 

 tial measurements made of the relation of these quantities show 

 the form of the electric wave passing the point C. The only me- 

 chanical difficulty is to construct a chronograph which will allow 

 C to be connected with the condenser, a small but accurately 

 determined time after A is connected with the battery. A heavy 

 wheel of brass is set in motion by a steel spring so that it sbsB 

 revolve exactly twice a second. The interval through which the 

 spring acts being always the same, a nearly constant velocity is 

 parted. The disc is divided into 500 equal parts. A 

 movable index serves to regulate the angle through which the 

 - between the two connection* to be recorded. The time 

 ot revolution of the disk was first determined by noting the fig- 

 ures read in succession under the film of a small* telescope, « hen 

 the disk was illuminated by half-second flashes of an induction 

 coil. The force of the spring and the position of the trigger re- 

 leasing it were adjtwte relocity was obtained. 

 Recently a condenser was discharged through a known resistance 

 for some interval indicated by the disk, and the time calculated 



