84 



upon both the distance and direction of motion of tlie moving magnet. 

 Wlien tlie magnet is near tlie core the detector is more sensitive wlien 

 the magnet is approacliing. but when some distance from the core the 

 detector is more sensitive wlien the magnet is receding. Both curves 

 indicate a maximum of sensitiveness at a distance from the core, the 

 distance being less when, the magnet is approaching than when receding. 



Removing the magnet and operating the transmitter tended to de- 

 magnetize the core. Then when the magnet was placed in position and 

 the transmitter again operated, as in Curve C, there was a relatively 

 greater change in the magnetism of the core than was obtained under 

 the conditions of Curves A and B. Hence the deflections in column 

 C are .greater than those in A or B. It is evident that the relative 

 change in the magnetization of the core would be greater still where 

 the magnetic field is reversed after each reading, as in Curve D. 



Since nickel is more susceptible than iron in weak magnetic fields, 

 and less susceptible in strong fields, it occurred to the writer that 

 a more uniform sensibility for varying distances between the moving- 

 magnet and core might be obtained by making the core of nickel. 



Four cores were made, each one being 5 cm. long, approximately .4 

 cm. in diameter, and being wound with two hundred turns of No. 

 36 copper wire. 



Core 1 consisted of 26 pieces of piano wire, .003 cm. in diameter. 



Core 2 of 10 pieces of piano wire and 10 pieces of nickel wire, .082 

 cm. in diameter. 



Core 3 of 2 pieces of piano wire and 13 pieces of nickel wire. 



Core 4 of 14 pieces of nickel wire. 



Table II gives the deflections at various distances between the- 

 magnet and each of the four cores, the magnet being moved one space 

 at a time and having its poles reversed after each reading. The data, 

 for three of the cores is plotted in Fig. 2. 



