THE ROYAL ARTILLERY INSTITUTION. 
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Dissimilar materials in contact gave uniformly the slow uniform results; 
especially teak and iron, and metal and iron. 
Similar materials in contact gave the unsteady, irregular results, more 
particularly iron and iron. 
Summary of results, 
1. From a variety of causes the frictional resistance of any combination 
of materials is so variable, that no absolute value for the coefficient can 
be given. 
2. That similar materials in contact are more irregular and jerky than 
dissimilar ones. 
3. That a pressure of 140 lbs. on the square inch can be used without 
incurring abrasion of the surfaces, while 560 lbs. on the square inch injures 
most of them. 
4. That varying the extent of surface has no practical effect on the 
value of the coefficient. 
5. That the frictional resistance varies directly as the total pressure up 
to the point at which adhesion sets in. 
6. That the frictional resistance varies directly as the number of surfaces 
acted upon by the pressure. 
7. That the highest coefficient is obtained with gun-metal and gun-metal, 
but the motion is irregular and violent, whereas gun-metal and iron, while 
giving nearly as high a coefficient, give a very slow and regular motion. 
8. That as respects compressors for gun carriages, the experiments 
appear to establish the following facts :— 
(1) That the materials used for the rubbing surfaces should be dissimilar, 
gun-metal and wrought-iron being the most suitable. 
(2) That the best pressure per square inch is from 80 to 120 lbs., and 
any resistance required beyond this should be obtained by increasing the 
number of surfaces in preference to increasing the pressure, 
Description of the Plates, 
Plate I. Sketch shewing the general arrangement of the apparatus and 
mode of conducting the experiment, 
Plate II. (Fig. 1). Curves, shewing the effect of varying the rate of motion 
with different materials, under a mean pressure of 1*5 tons. (Fig. 2) 
mean of the curves shewn in Fig. 1 with fair curve. 
Plate III. Diagram, shewing the coefficients of Series a at a common 
rate of motion of 8 inches per minute. 
[vol. VI.] 
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