AUSTIN: MUSICAL RECEPTION 223 



was bromcresol purple, the color changes of which occur just 

 to the acid side of the neutral point; with this indicator a yellow 

 color was obtained, indicating a specific acidity of at least 30. 

 The soil was accordingly tried again with methyl red, which lies 

 next toward the acid side, and this gave a violet-red color, cor- 

 responding to a specific acidity of 300 ot more. It was accord- 

 ingly necessary to try an indicator working at still higher acid- 

 ities, namely bromphenol blue; and this yielded a violet color, 

 indicating 300 or less. The last two indicators agreed, then, in 

 fixing the reaction of this soil as: specific acidity 300 (Pg = 4-5) • 

 In spite of certain limitations, this method is capable of giv- 

 ing definite information as to soil reaction in many cases. And 

 the results obtained by the writer on a number of species of 

 native plants, to be described shortly in other communications, 

 have been of such significance that the method is now published 

 for the benefit of students of plant distribution and others in- 

 terested in soil acidity and alkalinity. 



RADIOTELEGRAPHY. — Musical reception with continuous 

 waves without local oscillations, h. W. Austin, U. S. Naval 

 Radio Research Laboratory. 



The principle of what is now known as the slipping contact 

 detector or ticker, was first applied to the detection of direct 

 currents with the telephone by the author in 1900^ and later 

 applied to the reception of radio signals in 1906.^ 



This does not in general give a musical note in reception either 

 for damped or continuous oscillation, on account of the irregu- 

 larity of the contacts. If, however, a toothed wheel or any 

 equivalent contact maker, such as is shown in figure i, be pro- 

 vided with a brush bearing on the face of the wheel or axle in 

 such a way as to produce a steady contact, while a second brush 

 is adjusted so as to touch the teeth, musical reception 

 can be obtained with continuous oscillations. For this purpose 

 the alternating E. M. F. is impressed at DE and the wheel rotated 

 at such a speed that the contacts of the brush E are made with 



' Phys. Rev. ii: Aug., 1900. 



2 This Journal i: 6. 1911. Physik. Zeitsch. 12: 867. 1911. 



