722 Mr. J. J. T. Chabot on the Various Motions in 



Thus by combining with the iron or the constantan (say) 

 a " modifying " wire of another metal such as copper, the 

 line of the composite wire can be turned into more exact 

 parallelism to the line of the other metal used with it by 

 merely altering the resistance of one of the branches of the 

 composite wire. In the cases already mentioned the 

 "modifying" wire (copper) will have a circuit of relatively 

 high resistance. 



In measuring high temperatures with platinum-platinum- 

 rhodium (or Ptlr) junctions, a " modifying " wire of less 

 pure platinum, for example, would enable the thermoelectric 

 voltage-curve to be modified at will, and perhaps "normalized" 

 or even rectified. 



Teddington, Feb. 23, 1905. 



LXVII. Simple Diagram connecting the Various Motions in 

 the so-called Bohnenberger 's Machine. By J. J. Taudin 

 Chabot *. 



BOHNENBERGER'S machine f is but seldom noticed in 

 the general run of text-books on physics. This may 

 be partly due to the fact that an exhaustive numerical re- 

 presentation of its mode of action cannot be there given, but 

 partly it is also due to the circumstance that in consequence 

 of its remaining unnoticed it has gradually come to be re- 

 garded by many as a mere curiosity, instead of a necessary 

 part of the equipment of every well arranged physical 

 laboratory. 



Nevertheless this piece of apparatus presents a stimulating 

 means, whose value is not to be underrated, of demonstrating 

 the composition of motions, such as we already come across 

 in the parallelogram of velocities ; provided only that its 

 mode of action may be rendered plain in a correspondingly 

 simple manner. The following lines are an effort in this 

 direction. 



Let the massive disk be in the x-y plane, and its axis of 

 rotation along the z-axis of an orthogonal three-dimensional 

 system of co-ordinates xy z ; and let the direction of rotation 

 be R. (fig. 1). Then we have to distinguish two main com- 

 binations : (1) an independent torque, acting in the direction 

 R^, imparts to each element of the rotating disk as it passes 

 the .r-axis a tendency to move along a resultant R y . ; but 



* Communicated by the Author. 



+ " Beschreibung- einer Maschinezur Erlauterung der Gesetze derUm- 

 drehung der Erde umihre Achse imd Verauderung der Lage der letztern." 

 Tuebingen, 1817. 



