Currents by means of the "Phaseograph." 973 



II. Methods of Registering Characteristics. 



We can distinguish between two different kinds of charac- 

 teristics. 



A. Statical characteristics. 



B. Dynamic characteristics. 



A refers to stationary or quasi-stationary currents ; these 

 can be registered by ordinary voltmeters or ammeters. B, the 

 dynamic characteristics, occur with variable especially alter- 

 nate currents ; these must be registered by instruments which 

 at every moment indicate strength of current and voltage. 

 For this purpose various oscillographs with two movable 

 systems are used: one registering strength of current, the 

 other voltage. By the construction of the connected values 

 in a co-ordinate system the required characteristic is obtained. 

 Consequently, this is practically an indirect method, which 

 besides implies much waste of time. Another difficulty also 

 arises which makes the results uncertain, i. e. the defective 

 adjustment. The adjustment is effected by directing the 

 reflexions from the mirrors of the two movable systems 

 towards the same point. If these reflexions were, let us say, 

 geometrical circles with the same intensity of light, the 

 adjustment would, no doubt, be possible, but as they present 

 irregular figures, it can be done only with a limited degree 

 of accuracy. To this may be added also the circumstance 

 that the adjustment sometimes is altered while the instrument 

 is registering. On another occasion I will deal more closely 

 with this question. To avoid the difficulties just mentioned, 

 particularly the tedious redrawing of the curves, the two 

 movable systems must in some way be made to co-operate. 

 The apparatus I am going to describe is based on this idea. 



III. The Pliaseograph. 



In a communication to the Phy sikalische Zeitschrift * I have 

 demonstrated the chief features of the construction. As 

 shown by fig. 5 (PL XIX.), the apparatus consists of two 

 parts : the electromagnet and a box of brass with an ebonite 

 or slate lid. In the first construction the electromagnet was 

 made of two soft iron bows, each bar being provided with a 

 solenoid. This arrangement, however, proved useless. Of 

 the four magnetic fields required, only two were sufficiently 

 strong, i. e. those formed between the two bars of the same 

 bow. In the final construction the electromagnet was made 



* M. Siegbahn, Pliys. Zeits. x. 1909, p. 1017. 



