hertz's experiments. 205 



vil)rat(' ill its tail. How can a medium have those contraiy piopeitics!? 

 How can it oft'er au imjierceptible resistance to the comet, and yet take 

 up the vibrations of the atoms ? These are liard questions, and science 

 has as yet but dim answers to them, hardly to be dignified by the name 

 of answers — rather dim analogies to show that the properties su[)posed 

 to CO exist, though seeming contradictory, are not so in reality. 



One of the most beautiful experiments man knows — one fraught 

 with more suggestions than almost any hundred others — is that by 

 which a ring of air may be thrown through the air for many yards, and 

 two such rings may hit, and shivering, rebound. These rings move 

 in curved jiaths past one another witli almost no resistance to their 

 motion, urged by an action not transmitted in time from one ring to 

 another, but, like gravitation, acting wherever a ring may be, and yet 

 the air through Avhich they move can take u)> vibrations from the rings 

 showing thus that there is no real contradiction between the ])roperties 

 of things moving through a medium unresistedly in certain i)aths round 

 one another, and yet transmitting other motions to the medium. This 

 same air can push and pull, as wlien it sucks up waterspouts and deals 

 destruction in tornadoes. Hence there seems no real contradiction 

 between a medium that can imsh andjiull and transmit vibrations, and 

 yet offer no resistance to such fragile, light, and large-extended things 

 as rings of air. 



It is important to understand something about the properties that 

 this medium must have in order to explain light, electricity, and mag- 

 netism, because there is no use expecting a medium to possess contra- 

 dictory i)roperties. It is also well to recollect that for about tw^o hun- 

 dred years the existence of a medium by which light is propagated has 

 been considered as certain, and that it would be very remarkable if 

 this medium, which can be set in vibration by material atoms, acted 

 on matter in no other way. It seems almost impossible but that a 

 medium whicli is moved l)y atoms, and which sets them into motion, 

 should be able to mo\e sucli armies of atoms as we deal with in material 

 bodies. Even if we knew nothing of electricity and magnetism, it 

 would be natural to look for some imiiortant })liciioiiieiia. due to the 

 action of this medium on masses of matter. Th(> medium is n vera cttusa^ 

 and if it can be sliowii that tlie same set of properties by which electric 

 and magnetic forces are explained will also enable it to transmit vibra- 

 tions that have all the properties of light, it will surely be beyond a 

 doubt but that these electric and magnetic actions are those very ones 

 Ave would naturally expect from the medium that i»roi»agates light. 



Clerk 3laxwell some years ago showed that this was so, but as far as 

 any facts known at that time could prove, there were other theories of 

 electric and magnetic actions which ex])lained tlieir known i)henomenn 

 without the intervention of a medium. The matter stood somewhat 

 thus: The older thecuMes of <'lectric and nmgnetic force explained all 

 phenomena then known. These older theories assumed that electric 



