708 Mr. A. S. Eve on the Properties of 



If the original separation of the surfaces is less than 117 fifi, 

 as in the accompanying illustration, then the final distance 

 obtained before rupture will be less than 800 ////. 



For values of d between and 730 /*/* the curve given 

 follows very exactly the equation 



R = 4-5xl0- 16 ^ 6 , 

 R = resistance in ohms, 

 d = distance between surfaces in /*/*. 



It will, therefore, hardly do to assume that the conducting 

 bridge has a uniform cross-section throughout its length. If, 

 however, we consider it uniform when d equals 400 /z/x and B, 

 equals 2 ohms, i. e. before the extension has greatly increased 

 the resistance, then, assuming the material is pure platinum, 

 the diameter of the bridge is found to be 4'4 x 10"~ 5 cm. 

 This distance is considerably shorter than the mercury- light 

 waves used in this investigation, and consequently we need 

 not be surprised at our failure to observe by microscopic 

 examination any evidence of cohesion. 



The behaviour of the coherence, however, can very readily 

 be explained upon the assumption of the formation of a very 

 small metallic bridge which ruptures at once upon receiving 

 any sudden jar, causing a lateral movement, but which may 

 be stretched until it rapidly forms a neck and breaks, 



The process of the formation of the bridge is still un- 

 known. It is probable that an explanation of the production 

 of short spark-discharges will also make clear the coherer 

 action. C. K. 



LXV. The Properties of Radium in Minute Quantities. 

 By A. S. Eve, McGill University, Montreal*. 



IN a recent communication to the Physikalisehe Zeitschrift 

 (Dec. 1, 1904), A. Yoller has published some results 

 which appear to be diametrically opposed to the theory of 

 radioactivity, a theory which has already received a remark- 

 able amount of experimental confirmation. 



Yoller found that radium, distributed on a plate in minute 

 quantities and exposed to the air, disappeared or decayed in a 

 few days or weeks ; whereas other investigations lead to the 

 conclusion that radium, whether in larger or smaller quantities, 



* Communicated by Prof. E. Rutherford, F.E.S. 



