444 W. A. Norton — JExperiments on Contact Resistance. 



facts show that the application of the contact pressure was gen- 

 erally attended with a diminution of the coefficient of molecu- 

 lar resistance at the surface of contact. When the pressures 

 were renewed at short intervals, the contact set at first observed 

 was generally maintained, and often increased. 



The following table gives the diminutions of the contact dis- 

 tance obtained with the several weights, 2 oz., 4 oz.., 8 oz., 16 oz., 

 and 24 oz. It is to be understood that the numerical determin- 

 ations given in the table are the means of a number of individ- 

 ual determinations. It thus happens that the decimals are car- 

 ried beyond the reliable reading of the apparatus. The mean 

 results of diiferent sets of experiments are given in two instan- 

 ces. The apparent surface of contact was about ^^ of a square 

 inch, except in the case of the contact of a flat surface with a 

 round surface of sharp curvature, in which the area of contact 

 was too minute to be estimated. 



|lrononlron.| Same. 



Average. 



iron on iron. 



S„e. 1 a™«.. 





S...s.oot. 



s.... 





Znicr 



B.™. 





16 ;; 



0-000170 

 •000250 

 •000340 

 •000450 



•000285 

 -000325 

 •000425 

 •000500 



•000267 

 •000500 



•000410 



0;ofM62 



•0002'75 

 •000425 



*^.000257 

 •000297 





--- 



S. 



brE". 



ptIC 



Oeunaverage 



l^' 



jsorf. smooth. Surf, smooth. 



Surf, rough. 



Surf, polished 







'1" 



•000335 

 ■000500 



©•oooito 



•000250 

 •000256 

 •000410 



0^00^h5 

 •000267 



•000400 



-000212 

 -000294 



•o2m?5 



0^000i69 

 •000261 



•000404 

 •000493 



o.„Son 



0^00025 

 0-00029 

 000040 



On examining this table it will be seen, 



(1.) That the diminutions of contact distance were very 

 nearly the same, whatever was the nature, or condition of the 

 surfaces in contact 



(2.) That they were nearly independent of the extent of the 

 surface in contact ; since they were nearly the same when the 

 surfaces touched in a mere point, as when the surface of contact 

 had an extent of one-fourth of an inch by one-eighth of an 

 inch. 



(3.) That the diminution of contact distance for an increase 

 of one ounce in the pressure, was nearly inversely proportional 



