G76 



PHYSICAL FORCES. 



is at any instant moving in such a way as to 

 impress on a molecule of the mass B an ad- 

 ditional momentum in any given direction, 

 then the momentum of the molecule of B in 

 that direction will be diminished to an equal 

 amount. That is to say, to any mass of in- 

 creased motion propagated through the mole- 

 cules of B, there must be a reactive wave of 

 decreased motion propagated in the opposite 

 direction through the molecules of A. See, 

 then, the two significant facts, any addition of 

 motion which at one of these alternate periods 

 is given by the molecules of A to the molecules 

 of B, must be propagated through the molecules 

 of B in a direction me ay from A; and, simul- 

 taneously, there must tea, substruction from the 

 motion of the molecules of A, which will be 

 propagated through them in a direction away 

 from B. To every wave of excess sent through 

 one mass, there will be a corresponding wave 

 of defect sent through the other ; and these 

 positive and negative masses will be exactly 

 coincident in their times and exactly equal in 

 their amounts. Whence it obviously follows, 

 that if these waves proceeding from the sur- 

 face of contact through the two masses in con- 

 trary directions are brought into relation, they 

 will neutralize each other. Action and reaction 

 being equal and opposite, these plus and minus 

 molecular motions will cancel one another if 

 they are added together, and there will be a 

 restoration of equilibrium. 



These positive and negative waves of per- 

 turbation will travel through the two masses 

 of molecules with great facility. It is now an 

 established truth, that molecules absorb, in the 

 increase of their own vibrations, those rythmi- 

 cal impulses as waves which have periodic 

 times the same as their own ; but that they 

 cannot thus absorb successive impulses that 

 have periodic times different from then- own. 

 Hence those differential undulations being very 

 long undulations in comparison with those of 

 the molecules themselves, will readily pass 

 through the masses of molecules or be conducted 

 by them. Further observe, that if the two 

 masses of molecules continue joined, these posi- 

 tive and negative differential masses, travelling 

 away from the surface of contact in opposite 

 directions, and mutually arriving at the outer 

 surfaces of the two masses, will be fleeted 

 from these ; and, travelling back again toward 

 the surface of contact will there meet and neu- 

 tralize one another. Hence no current will be 

 produced along a wire joining the outer surfaces 

 of the masses, since neutralization will be more 

 readily effected by this return of the waves 

 through the masses themselves. But though 

 no external current arises, the masses will con- 

 tinue in what we call opposite electrical states; 

 as a delicate electrometer shows that they do. 

 And further, if they are parted, the positive 

 and negative waves which have the instant 

 before been propagated through them respect- 

 ively remaining neutralized, the masses will 

 display their opposite electrical states in a 



more conspicuous way. The residual positive 

 and negative waves will vhen neutralize each 

 other along any conductor that is placed be- 

 tween them ; seeing that the plus waves com- 

 municated from the one mass to the conductor, 

 meeting with the minus waves communicated 

 from the other, each being mutually cancelled 

 as they meet, the conductor will become a 35no 

 of least resistance to the waves of each mats 



Carrying out this view with great ingenuity 

 in the case of thermo-electricity and reaching 

 by it an explanation of the thermo-electric 

 pile, Mr. Spencer thus sums up the argument : 

 May it not be said, that by some such ac- 

 tion alone can the phenomena of electricity be 

 explained, and that some such action must in- 

 evitably arise under the conditions? On the 

 one hand, electricity being a mode of motion, 

 implies the transformation of some preexisting 

 motion implies, also, a transformation, such 

 that there are two new kinds of motion simul- 

 taneously generated, equal and opposite in their 

 directions implies, further, that these differ 

 in being plus and minus, and being therefore 

 capable of neutralizing each other. On the 

 other hand, in the above cases, molecular mo- 

 tion is the only source of motion that may be 

 assigned ; and this molecular motion must, un- 

 der the circumstances, produce effects of the 

 kind witnessed. Molecules vibrating at differ- 

 ent rates cannot be brought in proximity 

 without affecting one another's motions. They 

 must affect one another's motions by period- 

 ically adding to or deducting from one another's 

 motions ; and any excess of motion which those 

 of one order may receive, must be accompanied 

 by an equivalent defect of motion in those of 

 the other order. "When such molecules are 

 units of aggregates placed in contact, they 

 must pass on those perturbations to their 

 neighbors. And so from the surface of contact, 

 there must be waves of excessive and defective 

 molecular motion, equal in their amounts and 

 opposite in their directions waves which must 

 exactly compensate one another when brought 

 into relation. The cause alleged must cer- 

 tainly work some such effects as those describ- 

 ed. In this discussion it will be seen that Mr. 

 Spencer deals only with electrical phenomena, 

 of the simplest kind ; he, however, promises in 

 future to show how this hypothesis furnishes 

 interpretations of other forms of electricity. 



Interesting results have also been reached 

 during the past year in the field of radiation on 

 the connection of the radiants. "We are so ac- 

 customed to associate the word ray with the 

 idea of light, that the terms dark, invisible, or 

 obscure rays are not easy to realize in Iho 

 mind. Yet much the larger portion of the 

 sun's rays are of this invisible character, as 

 was discovered by Sir Wm. Herschel sixty-five 

 years ago. By passing a delicate thermometer 

 through the solar spectrum, he determined 

 the relative heating power, which he found 

 to increase from the violet to the red, and to 

 his surprise he also found that the dark spaca 



