.irruc.iiKKW or sr.trisTic.iL Mirnions 45 



Tho (iiu'stioiis wliicli must lu" answered from a coiisideralioii dI tliese 

 data arc typical. For example, we are interested to know how a 

 second series of observations may be expectctl to differ if the same 

 experiment were re|ieate(l. Tlie largest observed frequency corre- 

 s(Hinds to four alpha particles, although what assurance is there that 

 this is the most probable number? What is the probability that any 

 given numlx^r of alpha particles will strike the screen in the same 

 interval of time? Or again, what is the maximum number of alpha 

 particles that may be expcctwl to strike the screen? All of these 

 questions naturally can be answered providing we can deternune 

 the most probable frequency distribution. 



Statislital Xattire of Certain Telephone Problems. The character- 

 istics of some telephone equipment cannot be controlled within 

 narrow limits much better than the distribution of alpha particles 

 could l)e controlled in the above experiment. We shall confine our 

 attention primarily to a single piece of equipment. The carbon micro- 

 phone. For many reasons it is necessary to attain a picture of the 

 way in which a microphone operates. It is necessar\' to find out 

 why carbon is the best known microphonic material. In order to 

 do this we must measure certain physical and chemical characteristics 

 of the Ciirbon and compare these with its microphonic pro()erties 

 when used under commercial conditions. In the second place it 

 becomes necessary to establish methods for inspecting manufactured 

 product in order to take account of any inherent variability, and 

 yet not to overlook any ev'idence of a "trend" in the process of manu- 

 facture toward the production of a poor quality of apparatus. In 

 the third place it so hapfjens that the commercial measure of the 

 degree of control exhibited in the manufacture of the apparatus 

 must be interpreted ultimately in terms of sensation measures given 

 by the human ear. That is, the first phase of the problem is purely 

 physical; the second is one of manufacturing control and inspection 

 and the third involves the study of a variable quantity by means 

 of a methcKl of measurement which in itself introduces large variations 

 in the observations. 



In one of the most wideh" used types of microphones there are 

 approximately 50,000 granules of carbon per instrument. Each of 

 these granules is irregular in contour, porous and of appro.ximately 

 the size of the head of a pin. If such a group of granules is placed 

 in a cylindrical lavite chamber about J-inch in diameter and closed 

 at either end with gold-plated electrodes; if this chamber is then 

 placed on a suspension free from all building \ibrations and carefully 

 insulated from sound disturbances; if automalicalh' controlled 



