88 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



axis of which was horizontal and perpendicular to the meridian. The 

 connections of the apparatus are shown schematically in Figure 1. 



After the tube (Q) had been 

 placed in >S', the double 

 switch T was closed to the 

 left, so as to connect >S' with 

 the secondary (Z) of a 

 transformer the primary of 

 which was attached to the 

 alternating street circuit. 

 The secondary coil was so 

 suspended with counterbal- 

 ancing weights in a tall 

 fi-ame that it could be 

 moved at will in the direc- 

 tion of its axis to a distance 

 of several feet away from 

 the primary, and thus a 

 great number of alterna- 

 tions of a current gradually 

 decreasing in intensity 

 could be sent through S to 

 demagnetize the specimen 

 in it. 



31 represents a magnet- 

 ometer in the form of a 

 mirror galvanometer placed 

 in Gauss's B Position with 

 respect to Q ; the galvan- 

 ometer was so shunted by 

 an adjustable resistance JT 

 that the effect on the gal- 

 vanometer needle of the 

 partial current through the 

 coils of the instrument 

 almost exactly compensated 

 for the effect of the whole 

 current through the sole- 

 noid aS' when empty. B is 

 an adjustable rheostat of 

 200 ohms total resistance, designed to carry currents of some intensity, 

 K is a commutator, and IV a milliamperemeter furnished with a set of 



