July i6, 1891] 



NATURE 



249 



to the untechnically instructed. Its natural meaning implies 

 echo or reverberation, and has a definite relation to sound. 

 Now, although a sort of reverberation or repetition is part of the 

 effect intended to be denoted by the phrase resonance, yet the 

 most essential feature of that phenomenon, and the one most to 

 be emphasized in the recent extensions of the term, viz. the 

 accord of frequency or similar tuning between two vibrators, is 

 not connoted at all. Hence, even in acoustics the term is hardly 

 satisfactory, while its extension to other departments of physics 

 may be misleading. 



It was suggested, however, by Dr. Arthur Myers, that the 

 existing word avvrovos has almost exactly the right connotation, 

 and has no special limitation to sound ; while the derivatives 

 syntony, syntonic, and syntonise may readily become English 

 without exciting repulsion. 



The adjective " symphonic," suggested by the reporter of the 

 Physical Society, does not strike me as so good, because it 

 specially refers to sound again, and because the word "sym- 

 phony " has already another definite meaning. 



July 10. Oliver J. Lodge. 



Force and Determinism. 



I DO not think there are many non-physicists who will attempt 

 to gainsay the fact that, under physical constraint, the direction 

 of motion may be determined without affecting the quantity of 

 the energy concerned, and without expenditure of energy. 

 This is seen when the earth and sun revolve around their com- 

 mon centre of gravity, or when I twirl my stick around my 

 finger and thumb ; the earth and sun in the one case, and the 

 ferrule and knob of my stick in the other case, being bound 

 into one system physically. But I do think that an able and 

 clear-headed physicist like Dr. Oliver Lodge would be doing a 

 great service to non-physicists if he would, in your widely- 

 circulated columns, explain and solve, shortly and in non-tech- 

 nical language, the difficulties which trouble some of them ; 

 aiding them, for example, to comprehend the exact force of the 

 words expenditure of energy, and helping them to see that in 

 all known cases of change of direction of motion such change is 

 effected under physical constraint. It is when they are told by 

 a certain class of metaphysicians, who quote, or misquote, physics 

 in support of their assumptions, that physical motion is con- 

 trolled by will-power or volition, always acting at right angles 

 to direction of motion, and therefore leaving the amount of 

 energy unchanged ; it is then, I say, that they begin to grow 

 restive, and to demand definite and verifiable evidence that 

 such metaphysical constraint is (^pace Sir John Herschel) a neces- 

 sary or philosophical conception, and that it is impossible to 

 explain the phenomena without having recourse to it. If Dr. 

 Lodge would consent to help non-physicists in this way, and 

 would indicate what are the "important psychological con- 

 sequences " to which he alludes, he would be doing some of us 

 a good turn. C. Lloyd Morgan. 



University College, Bristol. 



As Prof. Lodge says he is glad to see that bis statement, 

 "although expenditure of energy is needed to increase the speed 

 of matter none is required to alter its direction," called in ques- 

 tion, and as he has so kindly answered one letter on the subject, 

 may I ask him to criticize the following remarks ? 



The theory of kinematics is based on certain geometrical con- 

 cepts, which may be summed up in the term space, and on the 

 concept of time. The laws of motion, together with the asser- 

 tion that mass is not a function of space or time, may logically 

 be regarded as implicitly defining mass and force. Energy may 

 similarly be defined, in terms of these kinematic concepts, as 

 'S,\mv. For I think the progress of science is tending to show 

 that the term " potential energy " is only a cloak to cover our 

 ignorance of the kinetic energies which for the moment have 

 escaped our ken. Hut in any case the statement quoted is 

 logically only a truism, deduced from the definitions of its 

 terms, and is therefore indisputable in all mechanical theorems. 

 But if it is to be applied outside the sphere of pure mechanics, 

 the moral will lie in the application of it — that is, it will be 

 necessary to examine, before applying it to any new subject- 

 matter, whether the definitions from which it was deduced apply 

 to that subject-matter or not. 



For example, by the third law of motion, mechanical force 

 only acts between tzvo masses, the momenta generated in them 

 being equal and opposite. If, therefore, psychic force is to 



NO. II 33, VOL. 44] 



come under the definition of mechanical force, it can only act 

 between two particles. And, therefore, if psychic force is to do 

 no work, by reason of its always acting in a direction normal to 

 the path of a particle, it can only act between two particles 

 whose paths happen to have a common normal — an occurrence 

 which must be infinitely rare. Edward T. Dixon. 



1 2 Barkston Mansions, South Kensington, July 4. 



Magnetic Anomalies. 



The discovery of very strong magnetic anomalies between 

 Charkov and Kursk in Russia, to which A. de Tillo has lately 

 referred in the Comptes rendus and in Nature, raises the 

 question whether the values there observed are strictly local, 

 or extend over a relatively wide area. Thus, it would be of 

 great interest to know if, on moving, say, some metres away 

 from a station, the declination and inclination hold the same 

 value. If not, there is clearly some cause which acts at a short 

 distance ; but if constancy is observed, a great step would be 

 taken towards the settlement of the question as to the existence 

 of strong variations common to a wide area. 



When magnetic anomalies are observed, the first thing to be 

 done is to ascertain whether the values found in a given locality 

 have a definite meaning— that is, whether they do not change 

 for slight displacements ; otherwise, the determination of the 

 magnetic elements has no meaning, as it is impossible to refer 

 them to geographical co-ordinates. 



The overlooking of this precaution has often led to serious 

 mistakes. Alfonso Sella. 



Biella, July 4. 



Physical Religion. 



As a constant reader of Nature from its commencement, 

 and the possessor of its forty-three and a half volumes, I venture 

 (after reading the review of " Physical Religion" in this week's 

 number) to ask if it is intended to develop it into a theological 

 journal. Because, however smart it may be to abolish Abraham 

 without "even taking the trouble to discuss" him, or to dispose 

 of Lux Mundi in a contemptuous sentence, it is hardly in 

 accordance with scientific methods. 



It is curious that many "Agnostics," though by their own 

 showing (if they would talk Latin instead of Greek) they are 

 Ignoramuses at best, should be so certainly sure of everything, 

 when a little reflection and modesty might satisfy them that as 

 '^Know-nothings" (in plain English) they have no more right to 

 deny than to assert. 



The standing motto of your title might be improved by the 

 addition of " Ne supra crepidam sutor." 



Hampstead Heath, July 11. B. Woodd Smith. 



SOME APPLICATIONS OF PHOTOGRAPHY} 



ONE of the subjects to which I propose to invite your 

 attention this evening is the application of instan- 

 taneous photography to the illustration of certain me- 

 chanical phenomena which pass so quickly as to elude 

 ordinary means of observation. The expression " instan- 

 taneous photography " is perhaps not quite a defensible 

 one, because no photography can be really instantaneous 

 — some time must always be occupied. One of the sim- 

 plest and most commonly used methods of obtaining very 

 short exposures is by the use of movable shutters, for 

 which purpose many ingenious mechanical devices have 

 been invented. About two years ago we had a lecture 

 from Prof. Muybridge, in which he showed us the appli- 

 cation of this method— and a remarkably interesting 

 application it was — to the examination of the various 

 positions assumed by a horse in his several gaits. Other 

 means, however, may be employed to the same end, and 

 one of them depends upon the production of an instan- 

 taneous light. It will obviously come to the same thing 

 whether the light to which we expose the plates be 

 instantaneous, or whether by a mechanical device we 

 allow the plate to be submitted to a continuous light for 



' Friday Evening Discourse, delivered at the Royal Institution of Great 

 Britain, on February 6, 1891, by Lord Rayleigh, F.R.S., Professor of 

 Natural Philosophy, R.I. ^ 



