Tribune Extras Lecture and Letter Series 



vibrations to a second the residual vibration was one- 

 eleventh of a second. Ho concludes that the whole ear 

 vibrates as one mass, and the durations of these oscilla- 

 tions of the whole car are far too short to remain one- 

 thirl ieth of a second. Ho thinks that this explains our 

 inability to distinguish the actual pitch of sound when 

 that pitch exceeds certain well-known limits. One of 

 the most remarkable deductions was that the duration 

 of tae sensation depends upon pitch rather than noon 

 Intensity. A considerable difr-reuce in intensity has 

 very little c licet upon the duration. 



Among the inferences which he draws from this 

 investigation is that tho timbre of a composite sound 

 brains to change at tho instant the vibrations causing it 

 ceu.e, ami tho residual sensation becomes more and 

 more simple till at last only tho simple sound of the 

 fundamental harmonic remains in the ear. Tnere are 

 analogous phenomena in respect to the sensation of light 

 to the eyes. Another deduction is that a composite 

 Bound can be aualyz <! by means of a revolving disc with 

 sectors cut out of it, interposed before the ear. Already 

 this line of research has cleared up many obscure points 

 in the theory of audition, and it bids fair to correct 

 many grave errors into which previous investigators 

 nave fallen. 



REFLECTION OF SOUND FEOM FLAMES AND 

 HEATED GASES. 



BY PROF. A. M. MAYER. 



This was a series of experiments showing 



that flames, heated gases, and cold gases of densities 

 differing from that of the atmosphere, can reflect sonor- 

 ous aerial vibrations, and tho exoorimeuts have also 

 given a measure of the reflecting power of flat ga flume. 

 Prof. Mayer was incited to this investigation by read- 

 ing the exceedingly interesting experiments of Prof. 

 Tyndal! on the stoppage of sound in a non-homogeneous 

 atmosphere, and the description of an apparatus devised 

 by Mr. Cottrell to Illustrate this, aud also a paper by 

 that gentleman on ''The Division of a Sound Wave by a 

 layer of Flame or heated gas into a reflected and trans- 

 mitted Wave." 



Prof. Mayer's method of ilHistration is simple and 

 easy of performance. He takes two similar resonators 

 and places tho planes of their mouths at right angles to 

 each other. Then in this angle he firmly llxes the tuning- 

 fork corresponding to tho resonators, so that tho broad 

 face of one of its prongs faces the mouth of one reson- 

 ator, while the space between tho prongs faces the 

 mouth of the other. Complete interference of the sounds 

 issuing from their mouths is obtained, and tho only 

 sound that roaches tho ear is the faint (sound given by 

 the fork's action on the air outside the angle included 

 )>v the months of the resonators. If in these circum- 

 stances we close the mouth of either oue of the resonators 

 with a piece of cardboard, the open resou itor will 

 Strongly reen force the sound of the forks. If we now 

 ro\erthc mouth of this resonator with, card-board, we 

 shall again have nili-nce. 



Now substitute for card-board, when both resonators 

 are open, the flume of a b.ii'.> wing gas-burner, with one 

 resonator, and use something more permeable to sound 

 than the card-board with the other. I5y trying a series 

 nl iimri! and more permeable diaph'-agm, it was found 

 that tracing paper just eqnab-d the i-ll'-et of the gafi- 

 flaino in guarding the mouth of the resonator from the 

 entrant of sound. A sheet of heated air above the gas- 

 burner was found to bo exactly equivalent to tho gas- 

 flame. The passage of a sheet of cold coal gas over the 



mouth of the resonator produced a similar effort; and sc 

 also did carbonic acid gas. though in less degree; but 

 cold, dry hydrogen closed the mouth of the resonator 

 more effectively than either of the above gases, though 

 not equal in this respect to the heated air above the 

 bat's wing flame. Among other curious results, Prof. 

 Mayer has ascertained that there is an absorption of 

 sound in the bat's wing flame; that the flame is heated 

 by the sonorous vibrations which enter it as sucb, and 

 isMie as heat vibrations. Ho has endeavored to obtain 

 a quantitative mathematical analysis of this absorption 

 and hopes for exact result?. 



TESTS OF THE STRENGTH OF PINE. 



BY PROK. W. A. NORTOX OF YALE COLLEGE. 



This paper was exceedingly elaborate, and 

 gave the results of a series of experiments on the sets or 

 residual deflections of pine sticks after having been 

 sui jected to a transverse stress. Tn 1839 Prof. Norton 

 demonstrated that th<i received theoretical formula for 

 the deflection of rectangular beams under stress re- 

 quired the addition of another term, varying directly as 

 the length and inversely as the breadth and depth of 

 the beam. Since then ho has been more recently ex- 

 perimenting upon residual sets or deflections. Tho 

 apparatus for testing was described at length and with 

 great detail. Great care was taken to guard against 

 incidental errors, especially in respect to consequences 

 of changing temperature during the stress. There was 

 evidence that alter repeated strains a molecular change 

 took place in the wood, and the effect of strain, after an 

 interval of rest, to a great extent not only passed awar, 

 but even left the stick with less set than it had a short 

 time before. A great number of curious and seemingly 

 contradictory results were obtained in the course of 

 these very numerous and varied experiments. As one 

 of the results obtained it appears that a load equal to 

 one-fourth of the breaking weight produces a perma- 

 nent set, and that repeated applications of this load 

 from day to day are attended with a continually in- 

 creasing set. It results that such wood should never be 

 subjected in any strncturo to one-fourth of its breaking 

 strain. 



Prof. Hilgard suggested that it was desirable to 

 use material for these experiments that could be 

 examined optically, such, for instance as glass. Ho 

 also Htigge.sted tho extreme similarity of Prof. 

 Thurston'a experiments upon tho torsion of pine 

 sticks. Prof. Norton was not inclined wholly to ac- 

 cept Prof. Thnrston's method of explaining the phe- 

 nomena. Prof. Hilgard mentioned that glass rods 

 took a set nnder torsion ; Prof. Henry urged the 

 use of homogeneous material in these experiments, 

 and Prof. Rogers suggested brass as a suitable sub- 

 stance; he agreed with Prof. Hilgard in regarding 

 the pine stick as a mere collection of fibers with 

 more or loss rosin between them. 



Tho proceedings of tho day were closed with tho 

 reading of a biographical sketch of Prof. Henry 

 James Clarke. 



