.IHSIK.ICTS ()/•■ Hr.l.l. SYSir.M TF.CIISIC.U. f.ll'I.RS 7(6 



('(|iiilil>riiin) witli tlit- hot til.imiiit. At '2l7r)''K the .is>uim<l M.ixwcll 

 ilistril)Uti()ii was viTiticd up to a ri'l.irding ()otnitial so j;ri'al that only 

 oiif oUrtron out of 10"" tniittrd fltctrons was al)lc to ri-arh the rolkctor. 

 It is Ik-IIi'mhI th.il Iho prisitit rtsiiits art- more reliable and extensive 

 than an\- hitherto obtained, .md that lhe\' are ronclnsive for electron 

 emission from tini^;tsen in a hijjh vaeuum. 



Electrons from Oxide Coated Platinum. SiibsiMiniMit measurements 

 by Dr. C Davisson have shown that the electrons emitted from 

 W'ehnelt cathiKles also have velocit\' components distriliiitetl according 

 to Maxwell's law. 



Aiitomobile-Xoise .\feasuretnent.'' H. ("i.vdk S.vook. Automobile 

 noise, although useful as a detector of mechanical imperfections of car 

 operation, is otherwise so extremely undesirable that elaborate methods 

 for analysis with a view toward pre\enting or suppre.ssing such noise 

 are warrantetl. The author presents an illustrated and detailed 

 description of the mechanism of luunan hearing, according to studies 

 nunle in the interests of teleiihonic transmission of maximum effective- 

 ness, enumerating and explaining the de\ices de\eloped for evaluating 

 the sources of sound and its modes of propagation and amplification. 



An automobile can be considered to be composed of a number of 

 acoustic resonators ha\ing \aried degrees of coupling between them, 

 ancl com])arisons are made of the \elocily of sound propagation through 

 the dirterent materials with that of its transmission in air, the \elocity 

 being greater in the structural material. The apparatus used for the 

 detection of ntiise and its measurement consists of \aried types of 

 equipment, divided into two classes; one includes the contact type 

 and the other the air-impact ty[)e, both being demonstrated. 



Following an enumeration of the ditTerent detectors and auxiliary 

 apparatus in use and comments upon the methods employed, it is 

 stated among other conclusions that it seems advisable to base loudness 

 measurements of automobile noise upon the difference of energ%- be- 

 tween the measured sound and an arbitrary standard of sound which is 

 the threshold of normal hearing; that, to locate the origin of automobile 

 noise, it frequently is sufficient merely to detect the noise without 

 measuring its loudness; and that, to identify the origin of automobile 

 noise, it often is of value to ascertain its component frequencies. 



'Jour. Sor. of .Automotive Knginpers. Vol. .\\ II, No. 1. \',i\:v 115. lul.. l'>2.^. 



