August 29, 1884.] 



SCIENCE 



183 



from that found from his first series of experiments, 

 and may be taken to be 299,800 kilometres per 

 second. 



It is remarkable how many of the playthings of our 

 childhood give rise to questions of the deepest scien- 

 tific interest. In spite of the admirable investigations 

 of Plateau, it still remains a mystery why soapy 

 water stands almost alone among fluids as a material 

 for bubbles. The beautiful development of color was 

 long ago ascribed to the interference of light, called 

 into play by the gradual thinning of the film. Some 

 of the phenomena are, however, so curious as to 

 have led excellent observers like Brewster to reject 

 the theory of thin plates, and to assume the secre- 

 tion of various kinds of coloring-matter. 



When the thickness of a film falls below a small 

 fraction of the length of a wave of light, the color 

 disappears, and is replaced by an intense blackness. 

 Professors Remold and Riicker have recently made 

 the remarkable observation, that the whole of the 

 black region, soon after its formation, is of uniform 

 thickness, the passage from the black to the colored 

 portions being exceedingly abrupt. By two inde- 

 pendent methods, they have determined the thickness 

 of the black film to lie between seven and four- 

 teen millionths of a millimetre; so that the thin- 

 nest films correspond to about one-seventieth of 

 a wave-length of light. The importance of these 

 results in regard to molecular theory is too obvious to 

 be insisted upon. 



In_ theoretical acoustics, progress has been steadily 

 maintained, and many phenomena which were ob- 

 scure twenty or thirty years ago, have since received 

 adequate explanation. If some important practical 

 questions remain unsolved, one reason is that they 

 have not yet been definitely stated. Almost every 

 thing in connection with the ordinary use of our 

 senses presents peculiar difficulties to scientific in- 

 vestigation. Some kinds of information with regard 

 to their surroundings are of such paramount impor- 

 tance to successive generations of living beings, that 

 they have learned to interpret indications, which, 

 from a physical point of view, are of the slenderest 

 character. Every day we are in the habit of recogniz- 

 ing, without much difficulty, the quarter from which 

 a sound proceeds ; but by what steps we attain that 

 end has not yet been satisfactorily explained. It has 

 been proved, that, when proper precautions are taken, 

 we are unable to distinguish whether a pure tone (as 

 from a vibrating tuning-fork held over a suitable 

 resonator) comes to us from in front, or from behind. 

 This is what might have been expected from an a 

 priori point of view; but what would not have been 

 expected is, that with almost any other sort of sound, 

 from a clap of the hands to the clearest vowel-sound, 

 the discrimination is not only possible, but easy and 

 instinctive. In these cases it does not appear how 

 the possession of two ears helps us, though there is 

 some evidence that it does ; and, even when sounds 

 come to us from the right or left, the explanation of 

 the ready discrimination which is then possible with 

 pure tones is not so easy as might at first appear. 

 We should be inclined to think that the sound was 



heard much more loudly with the ear that is turned 

 towards than with the ear that is turned from it, and 

 that in this way the direction was recognized. But, 

 if we try the experiment, we find, that, at any rate 

 with notes near the middle of the musical scale, the 

 difference of loudness is by no means so very great. 

 The wave-lengths of such notes are long enough, in 

 relation to the dimensions of the head, to forbid the 

 formation of any thing like a sound-shadow, in which 

 the averted ear might be sheltered. 



In concluding this imperfect survey of recent prog- 

 ress in physics, Lord Rayleigh said emphatically 

 that much of great importance had been passed over 

 altogether. He should have liked to speak of those 

 far-reaching speculations, especially associated with 

 the name of Maxwell, in which light is regarded as a 

 disturbance in an electro-magnetic medium. Indeed, 

 at one time, he had thought of taking the scientific 

 work of Maxwell as the principal theme of his 

 address. But, like most men of genius, Maxwell 

 delighted in questions too obscure and difficult for 

 hasty treatment; and thus, much of his work could 

 hardly be considered upon such an occasion as the 

 present. Maxwell's endeavor was always to keep 

 the facts in the foreground ; and to his influence, in 

 conjunction with that of Thomson and Helmholtz, is 

 largely due that elimination of unnecessary hypothe- 

 sis which is one of the distinguishing characteristics 

 of the science of the present day. 



In speaking unfavorably of superfluous hypothesis, 

 Lord Rayleigh did not wish to be misunderstood. 

 Science is nothing without generalizations. De- 

 tached and ill-assorted facts are only raw material, 

 and, in the absence of a theoretical solvent, have but 

 little nutritive value. At the present time, and in 

 some departments, the accumulation of material is 

 so rapid that there is danger of indigestion. By a 

 fiction as remarkable as any to be found in law, what 

 has once been published, even though it be in the 

 Russian language, is usually spoken of as t known ; ' 

 and it is often forgotten that the rediscovery in the 

 library may be a more difficult and uncertain process 

 than the first discovery in the laboratory. In this 

 matter, we are greatly dependent upon annual reports 

 and abstracts, issued principally in Germany, with- 

 out which the search for the discoveries of a little- 

 known author would be well-nigh hopeless. Much 

 useful work has been done in this direction in con- 

 nection with our association. Such critical reports 

 as those upon hydro-dynamics, upon tides, and upon 

 spectroscopy, guide the investigator to the points 

 most requiring attention, and, in discussing past 

 achievements, contribute in no small degree to future 

 progress. But, though good work has been done, 

 much yet remains to do. 



In estimating the present position and prospects 

 of experimental science, there is good ground for 

 encouragement. The multiplication of laboratories 

 gives to the younger generation opportunities such 

 as have never existed before, and which excite the 

 envy of those who have had to learn in middle life 

 much that now forms part of an undergraduate 

 course. As to the management of such institutions, 



