

538 Mr. G. "W. de Ttinzelmann : Mechanical Pressure of 



have also contributed greatly to our knowledge of the con- 

 nexion between the steady current curve o£ a detector and 

 its behaviour under electrical oscillations. 



Conclusion. 



The chief fact brought to light by the above experiments 

 is that the energy passed to the telephone by a detector is 

 connected linearly with the energy given to the detector in 

 the form of electrical oscillations. This is true for all the 

 detectors examined, even including the coherers discussed in 

 the earlier paper. The curves connecting the input and 

 output of energy though they are straight lines usually 

 pass some distance away from the origin. This implies that 

 for a particular detector under invariable conditions there is 

 a fixed wastage of oscillation energy, amounting commonly 

 to about 1/10 of an erg per second, however large or small 

 the oscillation energy given to the detector maybe. Another 

 interpretation is, however, that a small quantity of energy, 

 which is invariable while the detector is undisturbed, is 

 delivered by the detector to the telephone circuit in a form 

 lhat never makes any proportion of itself manifest as sound. 

 The curves suggest, though they do not prove, that all 

 detectors are fundamentally thermal in their action. That 

 this deduction is opposed to the conclusions reached by 

 previous experimenters is clear from the summary of their 

 work given above. The principal cause o± this difference 

 between our conclusions appears to be that nearly all previous 

 observers have used comparatively large quantities of oscil- 

 lation energy, and have therefore probably brought into 

 play phenomena that never arise in detectors as used in 

 wireless telegraphy. 



The above investigations were carried out by the aid 

 of a grant from the Royal Society's Government Grant 

 Committee. 



LIV. The Mechanical Pressure of Radiation effective on 

 the smallest as well as on larger Particles. By G. W. 



DE TUNZELMANN, B.Sc* 



IT has been pointed out by Prof. Schuster in a letter to 

 ' Nature' t that " there is a widespread impression that 

 light pressure acts only on particles the linear dimensions of 

 which include several wave-lengths of light, but this is not 



* Communicated by the Author. 

 t 'Nature,' vol. lxxxi. p. 97 (1909). 



