Note on the stereophotochromoscope : a new optical instrument / by David Fraser Harris.

  • David Fraser Fraser-Harris
Date:
[1895]
Catalogue details

Licence: Public Domain Mark

Credit: Note on the stereophotochromoscope : a new optical instrument / by David Fraser Harris. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    30 MEMBEANES OF EECOrvDlNG TAMBOURS. . ■ 14 20X14 -n ,. . . m -F-cm. . . — oscillations, o 0 or 56 per second] The oscillation usually gave a visible tracing for only -25, the amplitude rapidly dymg away after 3 or 4 oscillations. In other words, the inertia of the india-rubber membrane of a 4-5 cm. diam. Marey's tambour expresses itself in an oscillation having a rate of between 50 and 60 per second, being in this case elicited by mechanical agitation of considerable energy. I venture to think, therefore, that this alleged source of mechanical error can constitute an element of fallacy only in tracings of such movements as have a period somewhere between 50 and 60 per second. Provided that a time-tracing be simultaneously taken, the rate of the main series and of superimposed wavelets could always be estimated. Without doubt each tambour has a different period from every other, dependent upon the extent, the thickness, and the tension of its membrane, and upon the weight and length of its lever. Thus, in any investigation making use of such instruments, and especially when, in interpreting the curves, stress will be laid upon any small waves (rapid vibrations), or upon small waves superimposed upon larger (slower) ones, it would be necessary to determine, in some such fashion as the above, the proper period of the apparatus. According to my observa- tions, the instrumental oscillations, even when set up by con- siderable violence, tend to cease (or become so small as to give no tracing) in the comparatively short time of -25. Professor Haycraft seems to have elicited vibrations of a cardiograph by surprisingly gentle pressures—light taps of the finger upon the membrane. From the above observations I would scarcely have expected such slight agitation to have set up the proper period oscillations described by Haycraft with such care.^ The upper tracing he gives on p. 457 closely resembles several I obtained, and had it happened to be accompanied by a simultaneous time- tracing this note would be superliuous. ^ The Movements of the Heart within the Chest and the Cardiogram, Jour, of Physiol., vol. xii., 1891.