March 20, 1896.] 



SCIENCE. 



429 



not produce any change in the speed of A 

 or B, but the result of the collision is the 

 deflection of the paths of both and this de- 

 flection is proportional to their masses. All 

 this is simple in the collision of two free 

 bodies of a certain class, both of which are 

 in motion and which collide when their 

 paths impinge upon each other. But two 

 bodies, A and B impinge. A is with- 

 out molar motion ; B has molor motion. 

 Will B yield a part of its motion to A, 

 or will B retain its motion as in the 

 case of two free moving bodies and cre- 

 ate motion in A ? Or if A is unmoved and 

 B is stopped in its molar motion will motion 

 be annihilated ? If two molar bodies are 

 free and both in motion and their paths 

 impinge, neither particle has its speed in- 

 creased or diminished, but if one is at rest 

 it will be put in molar motion and it will 

 thus appear to have motion given to it 

 either by the creation of motion or by tak- 

 ing it from the other. The illusion involved 

 arises from this, that the molar body said to 

 be at rest is really not at rest. If they are 

 both free and in motion it is plain that one 

 does not yield motion to the other. But if 

 one of the bodies is in the state called rest it 

 appears that it is set in motion or that the 

 other body is brought to rest. In the first 

 case it seems that motion is not created nor 

 annihilated, in the second that motion is 

 created and in the third that motion is an- 

 nihilated. Is this true? This is the ques- 

 tion we are to answer. Can motion in any 

 body be created or destroyed by collision ? 

 It appears so, but we are to show that this 

 appearance is an illusion. 



Every particle of matter known to man is 

 in motion at a high velocity. This wooden 

 ball is in motion about the axis of the earth, 

 about the sun, and also with the sun about 

 some other point in the heavens. The sum 

 of all these motions considered as speed is 

 unknown, but it may be affirmed with safety 

 that it is very great. Let us call this the 



telluric motion of the ball, its motion with 

 the earth. Its path is composed of at least 

 three contemporaneous revolutions. How- 

 ever great the speed of the telluric motion, 

 it is> yet small as compared with other mo- 

 tions within the body itself. As now un- 

 derstood the woody tissue is composed of 

 cells, the cells of molecules, and the mole- 

 cules of atoms, all grouped in such a man- 

 ner by composed motion as to constitute a 

 tissue whose structure is preserved by mo- 

 lecular motion. That rigidity is sometimes 

 due to motion is well known. Stand by 

 the nozzle of a monitor with four hundred 

 feet of pressure behind the water and watch 

 the stream drive the great boulder away. 

 Strike this stream with a crowbar ; though 

 the iron may bend, the stream is unbroken. 

 So we may conceive that rigidity and 

 strength of structure are properties of mo- 

 tion. Let us call this rigidity and struc- 

 tural strength of the woody tissue consti- 

 tutional motion, whose force is equal to the 

 sum necessary to rend the ball into its con- 

 stituent atoms. The structural strength is a 

 measure of its constitutional motion, which 

 is great as compared with any molar motion 

 observed in the ball. Again the body exhib- 

 its a mode of motion known as heat,which is 

 undulatory or vibratory. Of the speed of 

 radiant heat something is known, and it is 

 well-known that it is very great as compared 

 with any molar motion observed in the 

 bodies which exhibit the heat. Let us call 

 this constitutional and thermic motion 

 molecular motion. 



I roll the ball over the floor, and molar 

 motion is exhibited to the vision. 



Thus we know of three kinds of motion 

 possessed by the body, but that which is 

 apparent to the unaided vision as molar 

 motion is but a minute part of the whole. 

 It is evident that it is a very small part of 

 the telluric motion. Let us now see what 

 proportion it bears to the molecular or the 

 constitutional and thermic motions com- 



