380 Application of van der Waals* 



Here we have assumed that N = 33 just as for the bullet. 

 For a 12-inch shot similar to the bullet the four quantities 

 just calculated for the 3-inch shot have to be multiplied by 4. 

 This makes the angle of departure 24° 28' and the range 

 24,000 yards, nearly 14 miles, while the lag of the axis of 

 the shot behind the line of flight is only 5'*1 and the de- 

 flexion of the axis to the right of the path (for right- 

 handed spin) is 1° 32'. Although the numerical results will 

 have to be modified to suit shells, it is clear from the results 

 worked out that the spin of a shot carries out very faithfully 

 the task of keeping the nose foremost during the flight, and 

 that the deflexion of the axis is less at effective ranges for 

 the larger shot than for the smaller ones. 



XXXV . On the Application of van der Waals 1 Equation of 

 State to Magnetism*. 



To the Editors oj the Philosophical Magazine. 



Gentlemen, — 



ALLOW me to make a few remarks with reference to the 

 paper published by Dr. J. R. Ashworth in the November 

 Number of the Fhilosophical Magazine, 1915. He finds for 

 a ferromagnetic substance the following relation between the 

 magnetization I, the magnetic force H, and the absolute 

 temperature T: • 



(H + a'P)(}-J o )=R'T, .... (1) 



as an analogy to van der Waals' equation. 



Moreover, he supposes the Curie temperature to be the 

 same as the critical temperature given by equation (1). If 

 we write the equation in the reduced form 



where 



Cs. _ 



■{& 



+ V)(| 



-0- 



3 = 



T 



= T C 



and 



T = 



c 



'' 27R" 



v= 



I 

 "I 



and 



Ic = 



I» 

 3' 



7 = 



H 

 = H„ 



and 



H.= 



a'V 



then the critical value of I is one. 



* [Some delay has occurred in the publication of this note owing to 

 the MS. having formed part of a mail which was captured by a German 

 vessel. — Eds.] 



