572 Intelligence and Miscellaneous Articles. 



2. Models of the kind described may therefore likewise belong 

 to either of two classes — one constructed with wheels whose teeth 

 form left-handed screws ; the other with wheels whose teeth are 

 right-handed. 



3. The properties of models of the two kinds are, when con- 

 sidered each by itself, identical ; but relatively to each other they 

 exhibit symmetrical inversion. 



4. On attempting to combine a constituent of one of the above 

 classes with one of the other class, it is found that it is possible 

 to make them gear into each other only when their axes of 

 revolution are parallel. Such a combination of helical -toothed 

 gearing with parallel axes has a similar property to a combination 

 with axes at right angles (the separate wheels being consequently 

 of the same kind) : a limited positive or negative acceleration of 

 the rotation of one of them causes the rotatory motion of both to 

 be partially transformed into motion of translation : the wheels 

 move in opposite directions along their axes of rotation until the 

 acceleration ceases or is replaced by one of opposite sign, and so 

 on (vid. Phil. Mag. loc. cit.). 



5. By combining with each other in different ways pairs of right- 

 handed and pairs of left-handed helical-toothed wheels (thus forming 

 at the same time one or more of the pairs mentioned in the last 

 paragraph), various closer combinations can be made, each of 

 which is distinguishable from the rest, and can in turn serve, as a 

 unit of a higher order, for building up a wheel-model with a regular 

 distribution in space, and with the described properties of trans- 

 forming rotatory motion into motion of translation. 



6. The number of possible models of this latter kind is, in general, 

 dependent upon the number of elements which go to the formation 

 of their constituents, — the more numerous these are, the longer in 

 each case is the series of the possible resulting combinations. 



Degerloch (Wiirtemberg), November 4th, 1898. 



To the Editors of the Philosophical Magazine. 



Gentlemen, 

 In the May number of this Magazine (pp. 432-447) Mr. A. P. 

 Wills has described a method of measuring with the balance the 

 susceptibility of diamagnetic and feebly magnetic substances. I 

 venture to point out that the same method was described by me 

 so long ago as 1889 {Tageblatt der 62 Versammlung deutscher 

 Naturforscher und Aerzte in Heidelberg, pp. 209-211), as used for 

 measuring the magnetic constants of Iron, Nickel, Cobalt, Oxide 

 of Iron and Bismuth, parallel and perpendicular to the lines of 

 magnetic force. The method effects for solids precisely what the 

 method I have given of measuriug magnetic forces by means of 

 hydrostatic pressure does for liquids ("Wiedemann's Annalen, xxiv. 

 p*p e 347-416, 1885), and has for ten years past been repeatedly 

 used in my Laboratory here, as for instance by Herr Paul Meyer 

 (Dissertation, Heidelberg, 1889 ; Electrotechnisehe Zeitschrift, x. 

 pp. 582-587); MaxAVeber (Wiedemann's Annalen, liv. pp. 30-43, 

 1895), and Ernst Seckelson (Dissertation, Heidelberg, 1898). 

 Univeisity of Heidelberg. Very faithfully yours, 



Phvsical Laboratory, G. Quincke. 



November 7, 1898 



