August 28, 1891.J 



SCIENCE. 



1 19? 



The doctrine of signatures depends on the notion that the 

 appearance of plants signify their use. The eye-bright, on 

 account of the eye-like spot in its corolla, is used for eyes; 

 the granulated roots of the saxifrage indicate its use for cal- 

 culous complaints; the human shape of the roots of ginseng 

 give it special efl&cacy; and the walnut, the parts of which 

 so closely resemble the skull and brain, is marked out for 

 the mental diseases. The doctrine of sympathies has ap- 

 peared under various forms, and has quite an important his- 

 tory. The common phrase, " Take a hair of the dog that bit 

 you," is a survival of this system, and shows that the logic 

 underlying it is nothing more than that two phenomena once 

 connected, either by coincidence or as cause and effect, will 

 continue to maintain this connection. Paracelsus describes 

 a peculiarly composed weapon-salve which was to be applied 

 to the weapon that caused the wound and thus heal the 

 wound. Sir Eenelm Digby's practices involve the same no- 

 tion. He procured a handkerchief or other personal belong- 

 ing of the patient, and when this was dipped in water, the 

 fever abated, and the like. The sympathetic alphabet was 

 another form of this doctrine. Two friends each cut a piece 

 of skin and grafted it on the skin of the other; on this was 

 tattooed an alphabet, and communication was established by 

 the belief that pricking a letter on the skin of the one friend 

 would cause a paia in the corresponding place of the other. 

 Even in the present century two Frenchmen announced the 

 discovery of a species of snails which, however widely sepa- 

 rated, would go through the same movements, so that if the 

 one is guided over an alphabet the other will rest upon the 

 same letters. 



The most systematic of all these pseudo-sciences is astrol- 

 ogy, the analogies underlying which being of all grades of 

 remoteness. The system of correspondences which it pro- 

 posed gave unusual opportunity for flights of imagination, 

 and no analogy, however far-fetched, was too slight for the 

 foundation of some doctrine. The accident by which the 

 planets were given the names of deities was sufficient to 

 connect the characters of those deities with the lives of per- 

 sons at whose births these planets presented especial relations. 

 Similarly the fact that constellations were named by fan- 

 cied resemblances to certain animals was sufficient to connect 

 one's career with the qualities of that animal; thus a child 

 born under the sign of a lion would be courageous, but one 

 born under the crab would not go forward in life. 



Amongst the various genei'alizations upon which these 

 considerations have bearing, attention will be called to the 

 following. The history of the argument by analogy adds 

 another link to the chain of evidence by which the develop- 

 ment of the individual is connected with that of the race. 

 We trace similar appearances amongst savages, amongst 

 children, and still more strikingly in those surviving forms 

 of superstition and pseudo-scientific systems which we are 

 warranted in regarding as reversions to more primitive types 

 of thought. Again, the principle that what was once the 

 serious business of adults serves in more advanced stages of 

 culture for the play of children or the amusement of leisure 

 hours, finds illustration here. Just as the drum, once the 

 terrifying instrument of the warrior, or the rattle, once the 

 potent implement of the medicine-man, has become the toy 

 of children, or as the bow and arrow are maintained for 

 sport only, so the outgrown forms of thought, the analogies, 

 that were serious to our ancestors, now find application in 

 riddles and puns When we ask, " Why is this one object 

 like another? " we are asking for just such out-of-the-way 

 resemblances as have been noted above. And, finally, in a 



variety of ways, the consideration of the argument by anal- 

 ogy adds to our appreciation of the unfoldment of mental 

 powers, of the slow and painful steps by which the tenets of 

 modern science have been gained, of the necessity for con- 

 tinued striving in this direction, as well as of the underlying 

 unity of movement and design by which these phenomena- 

 acquire their deeper and more human interest. 



THE ETHER.' 



It was with some fear and trembling that I selected as the' 

 subject of a brief address a subject of such vast dimensions, 

 and the feeling increased as it became more and more evi- 

 dent how difHcult it is to give clear expression to ideas that 

 are very far from clear. 



In former days many reasons were given showing the ne 

 cessity for the existence of an ether which do not seem con- 

 clusive now. We can scarcely appreciate the bearing of an 

 argument to the effect that there must be an ether or nature 

 would be disgusted with the major portion of space. We 

 should begin at once to wonder what there could have been 

 in the experience or training of any person that could lead 

 him to such a conclusion. We do not see the need of an 

 ether to hold up the stars and planets and prevent them fi'oni 

 falling to the ground. We do not try to explain by similar 

 means how the planets are kept in motion. 



We do, however, have other needs for ether, which seem 

 important and pressing; still we cannot help wondering oc- 

 casionally, with Theophrastus Such, what kind of hornpipe 

 we are dancing now. How will our ideas commend them- 

 selves to those who follow? 



For many years it was taught that the luminiferous ether 

 was an incompressible jelly-like mass, and that light is an 

 elastic pulsation in this medium. The elastic' theory, how- 

 ever, was burdened with serious difficulty. No , phenomena 

 corresponding to a vibration normal to the wave front could 

 be found, but mathematical analysis showed that such waves 

 should in general exist in an elastic medium. Green saw 

 that this wave would produce no optical phenomena if the 

 velocity were either zero or infinite, and concluded that it 

 could not be zero in a stable medium. Those who followed 

 him in time also accepted his conclusion that the ether was 

 incompressible, and that the compression-rarefaction wave 

 must travel with an infinite speed. So the matter stood un- 

 til 1865, when Maxwell proposed an electro-magnetic theory 

 of light. According to this theory of light no compression- 

 rarefaction wave should exist, and light was conceived to 

 consist of local electrical displacement in a plane at right- 

 angles to the line of propagation. 



The rival theory met with great favor. It gradually be- 

 came clear that Maxwell's theory of light was attended with 

 less difficulty than the elastic theory. Twenty-three years 

 later. Sir William Thomson brings a powerful reinforcement 

 to the elastic theory which changes the whole aspect of the 

 case. He simply suggests that the compression-rarefaction 

 wave could properly and logically be gotten rid of in the 

 elastic theory by making its velocity zero, instead of infinite, 

 as Green had done half a century before. What Thomson 

 did was to examine anew the ground upon which Green had 

 concluded that a zero velocity for the compression wave in- 

 volved an unstable state of the medium, and it was found 

 that such a conclusion did not follow. 



1 Abstract of an address before the Section of Physics of the American 

 Association for the Advancement of Science, at Washington, D.C., Aug. 19-25,.. 

 1891, by Francis E. Nipher, vice-president of the section. 



