1895.] Investigation of the Laws of Attrition. 



31 



On the other hand, from the general trend of the figures in the 

 table it would seem that, when rubbed by a softer substance, a certain 

 amount is always to be considered lost. (In the table when appears 

 it means that the amount, if any, is less than experimental errors 

 introduced.) No attempt has been made to deduce a relation con- 

 necting the several quantities here involved, as, unfortunately, the 

 figures themselves cannot be relied on sufficiently to warrant 

 doing so. 



Tables of Experiments. 



In the following tables the force is given in what are practically 

 arbitrary units. The numbers themselves are the number of lbs. 

 hung over the pulley in each experiment. To obtain the force pressing 

 the cylinders together, these must be, in the first place, increased in 

 the ratio of the leverage of the swinging frame. 



For the purposes of comparison the weights obtained, which are 

 given in the two parallel columns, have been divided by the number 

 of rotations made by the cylinders in each case and by the number 

 of units of weight acting over the pulley. In the tables, decimal 

 places have been omitted : these are given beneath each table in the 

 deduced mean. To bring the result to C.G.S. units it is necessary 

 to divide by the sum of the mean circumferences of the cylinders, 

 by the number of grams in a lb., by g, and to multiply by 77/69*75 

 the ratio of the leverage. From the pivot or axis of the swinging 

 frame to where the cord leading to the weight was attached was 

 77 cm., from the same point to the cylinder was 69*75. 



Quartz and Quartz. 



Weight per rotation 





per unit force. 



Force. 



t " 





28 



64 



82 



28 



57 



57 



28 



71 



50 



21 



66 



66 



21 



62 



90 



21 



66 



66 



18 



77 



77 



18 



44 



72 



18 



55 



61 



18 



94 



66 



14 



43 



57 



u 



76 



98 



Mean 



= 0-000068 





Mean circumference of cylinders { First c J linder = 17 ' 4 



I Second cylinder = 17*6 



