360 Tufts — Transmission of Sound 



through it. The data given in Table I are typical of the results 

 obtained. 



The length of the column of shot used in this particular case 

 was 69 centimeters. The successive differences in pressure 

 between the two ends of the column are given in centimeters 

 of water in the first column of the table headed M. The 

 columns headed A, B and C, give the times in seconds required 

 for a tenth of a cubic foot of air to flow through the materials 

 A, B and C respectively, under the corresponding differences in 

 pressure indicated in the first column. The next three columns 

 of the table contain the products of the pressures into the cor- 

 responding times of flow through the three sizes of shot A, B 

 and C respectively. An examination of these products shows 



Table I. 

 M A B C MxAMxBMxC C/A C/B 



1 



48-5 



101-0 



484*0 



48 



101 



484 



10-0 



4-8 



2 



31-5 



59-0 



283-0 



63 



118 



566 



8-9 



4-8 



4 



19-1 



31-1 



150-0 



76 



124 



600 



7-8 



4-8 



8 



13-6 



20-6 



79-0 



105 



165 



632 



5-8 



3-8 



16 



8-1 



13-1 



39-0 



130 



210 



624 



4-8 



2-9 



26 



6-4 



9'7 



24-0 



160 



252 



624 



3-7 



2-4 



that the times of flow through the different materials decreases 

 less rapidly than the pressure-gradient increases. This differ- 

 ence in rates is much more marked for the coarse materials, A 

 and B, than for the finer material C, and for all of the mate- 

 rials is more noticeable for the lower than for the higher pres- 

 sure-gradients. As a result of this, the ratio of the time 

 required for a given volume of air to flow through C to the time 

 required to flow through A or B at the same pressure, given in 

 the columns headed C/A and C/B respectively, is seen to be 

 different for different pressures. A comparison of these ratios 

 shows that they decrease in value as the pressure-gradient 

 increases. The results of the experiments may be summed up 

 in the following statement : 



As the pressure-gradient for either of the materials A, B or 

 C is increased, the rate of flow of air through the material 

 increases less rapidly than the pressure-gradient, within the 

 range of pressures investigated. This difference of ratio of 

 increase is more noticeable for the coarse than for the fine 

 shot, and as a result of this, the numbers expressing the rela- 

 tive rates of flow of air through A and B as compared to C, 

 become smaller as the pressure-gradient increases. This is 

 equivalent to the statement that the resistances offered by the 

 three sizes of shot to the flow of air through them, become 

 more nearly equal as the pressure-gradient increases. The 

 pressure-gradients used varied from 0*01 to 0*60 of a centi- 

 meter of water per centimeter length of material. 



