iga 



SCIENCE. 



[Vol. XXII. No. 557 



velocity indefinitely great) would seem to give the idea 

 that the velocities are enormously great sometimes. 



But it would appear that there are distinct physical 

 conditions tending to limit the velocities of the molecules 

 of a gas [i. e., the velocities cajsable of being acquired in 

 the accidents of collision). First, there is the friction of 

 the molecules in their passage through the tether. This 

 must be considerable at high velocities, since meteoric 

 dust is measureably retarded from this cause; and the 

 relative friction or resistance to passage increases as the 

 size of the body diminishes. So that probably by the 

 known small size of molecules, the friction must be very 

 great. Second, the resistance to passage is augmented 

 from the fact that the molecule is in vibration (or some 

 analogous motion about its centre of gravitv) in the 

 sether. The molecule is like a rough body then, stirring 

 up the fether during its translator^ motion, which must 

 greatly augment the resistance to passage. That there 

 is friction in the gather hj the passage of molecules is 

 also confirmed, as it seems, by the fact that waves of heat 

 and light contain energy. For how should a vibrating 

 molecule impart energy to the tether without friction or 

 resistance ? The resistance is, in fact, a measure of the 

 energy imparted. It ap73ears a question whether, if the 

 amplitude of the vibration (or motion which stirs up the 

 aether) of molecules were known, the friction or resistance 

 could not be calculated therefrom. For we know the 

 number of vibrations accurately by the spectroscope, 

 and the energy imjjarted to the asther (or contained 

 in the waves), by the thermojDile. To deduce the resist- 

 ance to passage represented by the act of vibrating or 

 swinging, we only ajjpear to require the amplitude of 

 vibration then. Perhaps a limiting value for this could 

 be approximately arrived at. 



Another cause tending to reduce the velocity of trans- 

 latory motion possible to the molecules of gases in the 

 accidents of collision, consists obviously in the fact that 

 the internal motion of the molecule (vibration, rotation, 

 &c.) is proportional to the translatory velocity. So if a 

 molecule attained an excessive translatory velocity, it 

 would acquire an excessive vibration. This vibration 

 would soon dissipate the energy in the tether in the form 

 of waves of heat; and at the next succeeding collisions, 

 the molecule would acquire a relatively slower translatory 

 motion, as it could not retain the necessary vibratory mo- 

 tion (internal motion) which is the essential accompani- 

 ment of a very high translatory velocity. So, therefore, 

 from all these causes, the speeds capable of being ac- 

 quired by the molecules of gases in the accidents of their 

 encounters, are probably moderate; and far less, perhaps, 

 than might be inferred from the theorem that the veloc- 

 ities vary between zero and a velocity indefinitely great. 



Eeferring to a letter received from the late Prof. Clerk 

 Maxwell, I find that — "The number of molecules whose 

 velocity is more than five times the mean velocity is an 

 exceedingly small fraction of the whole number, less than 

 one millionth. But if there were 10'°° molecules, many 

 millions of these would have velocities greater than five 

 times the mean, and yet this would produce no appreci- 

 able effect on the whole mas's." 



It seems, then, from the above that the number of 

 molecules attaining high speeds is relatively rare. But 

 it appears none the less worth noting distinctly that an 

 indefinitely great velocity would mean a velocity indefi- 

 nitely greater than the speed of light even. Suppose a 

 few molecules to attain extreme stellar velocities of say 

 200 miles per second; it is evident that the friction in the 

 sether (appreciable in the case of meteoric dust) would 

 commence to tell in reducing the velocity. And as for a 

 molecule su^iposed to acquire the speed of light itself, 

 the molecule would (in traversing the tether) resemble 

 much a cannon ball moving through the air at the normal 



speed of the air-molecules themselves — about 1600 feet 

 per second — where the resistance to passage is very con- 

 siderable, so it seems that there are in practice physical 

 conditions limiting the velocities attainable by the mole- 

 cules of gases; the resistance to passage augmenting 

 more than in proj^ortion to the velocity. It is not at all 

 as if those molecules were moving in empty space. A 

 molecule, if assumed to acquire an infinite velocity, would 

 certainly have to be assumed to possess an infinite 

 energy. It may be questioned whether even the total 

 energy of translatory motion of the stars in the collective 

 universe is infinite in sum; if not, then a single molecule 

 with a supposed infinite velocity would require to have 

 a greater total energy than this. The expression "infinite 

 velocity" apparently only comes into the mathematical cal- 

 culations aj^plicable to a gas, supjjosed infinite in extent. 

 But in these calculations it seems tacitly to be supposed 

 that the molecules are moving in empty space, which is, 

 however, not a fact. On the contraryf, the molecules 

 move in a resisting substance whose obstruction to motion 

 increases in a high ratio with the velocity of the bodies 

 which traverse the resisting substance. 



DISCOVEEY OF ANOTHEE ANCIENT AEGILLITE 

 QTJAEEY IN THE DELAWAEE VALLEY. 



BY H. C. MERCER, DOYLESTOWN", PA. 



On June 23, 1893, with the help of my assistant, Ed- 

 ■ ward Frankenfield, I discovered another ancient argillite 

 quarry, on the left bank of Neshaminy Creek, on the War- 

 ner farm, about three-quarters of a mile above the mouth 

 of Mill or Labaska Creek (Bucks County, Pennsylvania). 



No artificial hollows as at Graddis Eun have yet been 

 found in the surrounding woods, but the rock here rising 

 in a low cliff above the stream is argillite, and the water 

 eating away the bank below it has revealed layers of chips, 

 charcoal, large worked masses, pitted as if to split with 

 the grain, pebble hammer stones and " turtle backs." A 

 broken yellow jasper spear blade was found by Franken- 

 field 100 yards higher up the stream. 



While the Gaddis Eun quarry (noticed in Science of 



f The late Prof- Clerk Maxwell arrived at some data as to the 

 size, etc. , of molecules. If we assume a hydrogen molecule to 

 vibrate through an amplitude (say) two-thirds of its diameter at 

 a certain temperature, we can obviously get the total distance 

 traversed through the sether in one second by the molecule 

 through its vibrations, i. e., the total distance equal to the sum of 

 the amplitudes of all the vibrations of the molecule in one second. 

 That is, add together all the amplitudes, and find what distance 

 that would make in a straight line. The size of the molecule is 

 taken from Maxwell. I find this distance to be about ninety 

 miles, i. e. , the molecule vibrates at the rate of ninety miles per 

 second, by the above assumed amplitude of vibration in terms of 

 ■dimensions of molecule (which seems quite possible). According to 

 Maxwell, two million hydrogen molecules placed in a row would 

 occupy a millimetre. Hence it appears practicable that molecules 

 can vibrate at a greater rate than a planetary velocity, which 

 may seem surprising to some, considering how small the dimen- 

 sions of molecules are (and therefore their amplitudes of move- 

 ment). The velocity of the earth in its orbit, for instance, is 

 eighteen miles per second, as is known. The above comparative- 

 ly high estimate for vibratory velocity of molecules (ninety miles 

 per second, only a rough estimate, of course) may account ration- 

 ally for the energ)' contained in the heat-waves of gases and 

 other bodies, which (energ}') is a measure of the friction or re- 

 sistance opposed by the sether to the vibration or movement of a 

 body in it. Calculations of this kind, although, of course, only 

 approximate, may give us conceptions or ideas of the sether struc- 

 ture. If I had by me data as to the energjr of the waves emitted 

 by a gas (radiating power), it would obviously not be difficult to 

 compute the static resistance opposed by the sether to the vibra- 

 tory movement or swing of the molecule in it, in terms of the 

 weight of the molecule, i. e., in terms of gravity. Whether we 

 have here a swing of the molecule, a movement of rotation oscil- 

 latory in its nature, or any movement of a repeated kind, the 

 same considerations evidently in principle apply. In the above 

 computation, the wave length of a hydrogen molecule is taken to 

 average one thirty-nine thousandth of an inch. 



