THE 110 YAL ARTILLEliY INSTITUTION. 
129 
motion are stated in Table XXXVIII. and the curves due to them are 
drawn in Tig. 1, Plate II. A general mean of all the coefficients is given 
in Table XXXIX., from which a single fair curve is obtained, Tig. 2, 
Plate II. 
Troin this fair curve a table of variations is made, due to a rate of 8 inches 
per minute (Table XL.) by means of which, assuming that the fair curve 
represents generally the variations of all coefficients at different rates of 
motion, the coefficients of Series a may be reduced to a common rate of 
motion, for the purpose of obtaining a stricter comparison. 
This is done in Table XLI. and the diagram, Plate III. represents their 
relative values, the shaded part being the mean coefficient of the different 
surfaces. 
General remarks on the experiments . 
Tor the following reasons it is considered that the blow did no more than 
destroy the adhesion which the pressure set up between the surfaces:— 
1st. If there were not sufficient weight to overcome the friction of 
motion; when the piece was struck, it moved through a space proportional 
to the force of the blow (varying from Jth to -j^-th of an inch) and 
came to a dead stop. 
2nd. When the proper drawing-through weight was reached, the piece 
continued to move at a higher or lower rate of motion according to the 
nature of the surfaces. 
3rd. If the blow were increased beyond that absolutely needed to break 
the contact of the surfaces, it simply had the effect of driving the piece a 
little more during the instant of impact; the rate of the continuous motion 
being unaffected by it. 
The blow therefore corresponded, although in a much smaller degree, 
with the violent shock which is felt in the first instant of discharge 
throughout the carriage and platform, and which must result in effectually 
destroying any force of adhesion between the surfaces of the compressor; 
hence the frictional resistance of the compressor during recoil, and of the 
specimens while in motion were developed as nearly as possible under the 
same conditions, both being comparatively free of the force of adhesion. 
The force of the blow needed to establish motion was found to vary with 
different materials, and was not required at all in the case of some—notably 
gun-metal and iron—the natural inference from this is that some surfaces 
are less disposed than others to adhere or lock into one another, especially 
as in all cases where the surfaces in contact were of the same material, and 
therefore of the same molecular construction, the cohesion was greatest and 
needed the greater blow to destroy it and set up motion; and where dis¬ 
similar materials were employed, the blow was of diminished force, or not 
needed at all, and hence the tendency to adhesion was less or had not begun 
to develope itself. 
It was noticed that the tendency of some surfaces to cohere was so great 
that it was not possible to keep up a uniform continuous slow motion. 
Sufficient weight was needed in the scale pan to make the piece move with 
a certain velocity before adhesion could be fairly overcome, hence the 
surfaces which had no tendency to adhere, as metal and iron, would slide 
