216 Mr. K. R. Johnson on the Theory of the 



5. The intensity of the diffuse reflected light with the 

 angle e constant and with varying angles of incidence i is 

 not proportional to the cos i, as Lambert assumes, 



6. The intensity of the diffuse reflected light with the 

 angle i constant and the angle e varying is proportional to 

 cos €, or Lambert's law of emanation is strictly correct for 

 absolutely matt surfaces without any exception. 



7. The so-called law of the cosine (q = T 2 .ds. cos i cos e) is 

 not true in consequence of the deviations of the law of tbe 

 cos i. The deviations range between 4*6 per cent, and 

 10 per cent. 



In conclusion I wish to return my best thanks to Prof. 

 Dr. von Lommel, who drew my attention to this interesting 

 branch of optics. I am also greatly indebted to Prof. Dr. 

 Seeli«er and Prof. Dr. Graetz for the interest shown bv 

 these gentlemen. 



Munich, Physical Laboratory of the University, 

 December 1899. 



XIV. On the Theory of the Function of the Condenser in an 

 Induction- Coil. By 1\. R. Johnson, Filosojie Licentiat *. 



IN a memoir " On the Function of the Condenser in an 

 Induction-Coil," T. Mizuno has published in May 1898 1 

 a research on the relation between the capacity of the con- 

 denser, the intensity of the primary current, and the secondary 

 spark-length. His results can be theoretically explained as 

 follows : — 



If the condenser is inserted across the interruptor in the 

 primary circuit, the extra current darts into the condenser ; 

 and if the maximum of the potential-difference in the con- 

 denser is very great, a spark takes place in the interruptor, 

 and thus the oscillations in the circuit are diminished by the 

 spark. If the capacity of the condenser is very large, the 

 maximum of potential-difference in the condenser and the 

 interruptor is small and unable to make a spark. Thus, 

 the efficiency of the induction-coil is greatly increased by a 

 little increasing capacity as far as the discharge by spark at 

 the interruptor diminishes ; when this spark is entirely sup- 

 pressed, the efficiency of the induction-coil is greatest and 

 the secondary spark-length a maximum. The capacity of the 

 primary condenser being further increased, the efficiency of 

 the induction-coil is diminished by the reason that the 

 maximum potential-difference in the condenser is diminished 



* Communicated by the Author, 

 f Phil. Mag. xlv. p. 447. 



