416 Intelligence and Miscellaneous Articles. 



to the structure of dendrites. The dendritic form starts from the 

 part farthest from the axis, and the flow of material is from 

 the smaller to the larger branches, the smaller uniting to form the 

 larger. The author explains dendritic structure by the formation 

 of a fissure in rock which becomes filled with a thin film of 

 dendritic material ; if the fissure is slowly widened, the dendrite 

 starts where the widening commences, coinciding dendrites being 

 formed on each wall. This theory is in accordance with many of 

 the characters of dendrites, such as their method of occurrence, the 

 nature of the material, and their uniformity in thickness. 



XXXIX. Intelligence and Miscellaneous Articles. 



ON THE THEORY OF THE FUNCTION OF THE CONDENSER IN AN 

 INDUCTION-COIL. BY DR. B. WALTER. 



TWO years ago Mr. T. Mizuno published in this Magazine* 

 -*- some observations on the relation connecting the spark-length 

 in the secondary of an induction-coil with the capacity of the con- 

 denser in the primary. These observations have recently induced 

 Mr. K. R. Johnson % of Stockholm, to offer a theoretical expla- 

 nation which, it is true, is correct, but which in my opinion presents 

 as little novelty as the experiments themselves. In fact, some 

 time before the appearance of Mizuno's paper, I published an 

 article J containing not only an account of an identical series of 

 experiments, but also a detailed theory of them. This article of 

 mine has been passed over unnoticed by Mr. Johnson, although 

 it was expressly mentioned by Mr. Mizuno, and in all probability 

 served as a basis for the latter's experiments. 



In one particular, indeed, these experiments appeared to offer a 

 contradiction to my theory, viz., in that the capacity of the con- 

 denser for maximum spark-length was greater the greater the 

 primary current. An explanation of this fact — first discovered by 

 Mr. Mizuno — has not been attempted by Mr. Johnson. Now in a 

 later communication by myself § the fact is hinted at in the 

 remark that with increasing current the primary spark becomes 

 stronger — a phenomena which of course vitiates the theory. 

 Ou the other hand, the relations once more recently discussed by 

 Mr. Johnson I regarded as having been already established in my 

 previously mentioned article. 



Hamburg, State Physical Laboratory, 

 March 1900. 



* T. Mizuno, Phil. Mag. xlv. p. 447 (1898). 

 t K. R. Johnson, ibid. xlix. p. 216 (1900). 



| B. Walter, Wied. Ann. lxii. p. 300 (1897) ; Electrical Review, xli. 

 pp. 529 & 597 (1897). 



§ B. Walter, Phil. Mag. xlvi. p. 172 (1898). 



