140 Dr. E. Warburg on the Heating produced in 



thence to be concluded that a thinner and thicker tube, the am- 

 plitude of whose vibrations is the same, develope equal amounts 

 of heat in the unit of section, that in the above experiments the 

 thinner tube was only heated more strongly because the ampli- 

 tude of the oscillations was greater in it; the latter is also seen 

 in the circumstance that the note of the system is distinctly 

 louder when the thinner is replaced by the thicker tube. 



The investigation of self-sounding lead tubes led to the same 

 result. Of three tubes of the same thickness of tubing and 

 length, 



A tube of 16 millims. external diameter after brisk rubbing 

 gave no deflection at the node. 



A tube of 9 millims 200 divisions. 



A tube of 4 millims 600 „ 



The intensity of the deflection decreased the greater the distance 

 from the node, and in the loops there was virtually no heating 

 at all. There can be no doubt that here the stronger heating of 

 the thinner tubes is simply explained by the fact that when the 

 same amount of force is used to excite the tone, the amplitudes 

 of vibration in the narrow tubes must be greater than in wider 

 ones ; for with wider ones a greater mass is set in motion than 

 with narrower ones. 



After it had been thus established what arrangement of the 

 experiment produced the greatest increase of temperature by 

 sounding, it was easy to demonstrate such a heating also in other 

 bodies. The only plan, however, was to connect the metals in 

 the form of thin wire with the sounding body, and then to put 

 this into powerful vibrations. A brass wire \\ to 2 millims. in 

 diameter, the length of which was half the wave-length of the 

 tone of the glass tube, indicated heat in the node corresponding 

 to 100 divisions. If by shortening the wire the strength of the 

 resonance was increased, 300 divisions were obtained. Then 

 come, in decreasing order of intensity of temperature observed, 

 copper, iron, steel, wood. 



A body very remarkable for its deadening properties is caout- 

 chouc ; and hence it is not surprising that on a short piece of 

 caoutchouc tubing being fastened to the sounding glass tube 

 a heating of more than 1000 divisions was obtained. A ther- 

 mometer which, laid on before the experiment, showed 19°, rose, 

 after the sounding, to 21° ; the actual increase in temperature 

 amounted therefore to 2°. 



While in tubes of other materials when several nodes are formed 

 the increase of temperature on the various nodes is much the 

 same, in the case of caoutchouc this is only perceptible at a small 

 distance from the place where it is fastened on the glass tube. 



