August 25, 1916] 



SCIENCE 



283 



5 Colby silt loam. Apparently the greatest 

 injury caused by grinding for one hour is 

 noted in the case of sandy soils. 



"When the soils were ground for 8 or 24 

 hours, there was an enormous decrease in the 

 bacterial flora. This is readily noted from the 

 figures of the last three soils given in Table I. 

 After 24 hours of grinding the soil was rend- 

 ered almost free of bacteria. 



It is of interest in this connection to note 

 the effect of long grinding on other soil organ- 

 isms, e. g., soil protozoa. Dilution counts on 

 various culture solutions adapted to protozoa 

 showed that the unground soils contained pro- 

 tozoa in dilutions greater than 1 to 10,000, 

 while in many cases the ground soil failed to 

 show any growth of protozoa. The garden soil, 

 No. 12, contained protozoa in the first dilution, 

 one gram in 10 c.c. of the medium. When 

 ground for 24 hours this same soil did not 

 show the presence of protozoa. 



From the results, it seems fair to conclude 

 that grinding soil in a ball mill injures the 

 soil microorganisms. If this process is con- 

 tinued for several hours, the soil will be par- 

 tially sterilized. Although no definite study 

 has been made, it is most probable that the 

 larger forms of plant life as fungi, yeasts and 

 algse suffer the same fate as the protozoa and 

 bacteria. 



E. B. Fred 



TJniveesity of Wisconsin 



an acoustic demonstration bearing on 

 the pulse theory of radiation 



Some years ago I made the acquaintance of 

 the " pulse theory " of radiation. As I under- 

 stood it then, the periodicity of any mono- 

 chromatic light as observed by means of a 

 spectral system was a function of the instru- 

 ment of dispersion. If so, how various sources 

 could give different spectra when their radia- 

 tion was dispersed by the identical instrument 

 was to me an unanswered question. It was 

 unthinkable that there should not be some 

 characteristic difference between the pulses, or 

 their manner of succession, in the two cases. 



The demonstration which I am about to 

 describe developed as the result of a more 

 recent informal discussion of the subject in 



this laboratory. It occurred to me that the 

 acoustic analogy of such a theory should have 

 as its consequence this fact : that an irregular 

 series of impacts would cause wave disturb- 

 'ances in the air such that a resonator of any 

 period, within certain limits, should respond. 



Such a series of impacts was furnished by a 

 stream of sand-particles falling against an 

 inclined paper surface, and the resonator was 

 the classic glass bottle, which was made to 

 respond to different periods by introducing 

 different amounts of water. 



Essentially the experimental set-up (which 

 was about twenty minutes in construction) 

 consists of a vertical glass tube of 7 mm. bore, 

 constricted to about 4 mm. at a point near its 

 top and some 42 cm. from its lower end; of a 

 funnel, whose expanded end is covered with a 

 rather loose diaphragm of thin tracing paper; 

 and the resonator described. The sand was 

 allowed to flow through the constriction in the 

 tube, and the stream subsequent to this was 

 kept from spreading too much by the portion 

 of the tube below, falling freely a distance of 

 12 cm. from the lower extremity of the latter 

 before striking the diaphragm (Fig. 1). The 

 sand was what is known to the drug trade as 



