From the Archive of P. N. Lebedev

22. VI. 01

INSTRUCTIONS FOR STUDENT ZERNOV (1)

Your work has taken such definite shape that, in leaving Moscow for this winter, I need draw your attention only to a few particulars.

1) Observation with Reilly’s large circle, with which you have been practicing, cannot be used for a final determination of the decrement, since the large disk changes too strongly the hole of the resonator and all its properties. That is why you should attach no importance to the difference that you will find between your observations and Leiber’s results [2].

2) For the final observations ask Nikol. Petrovich [3] to give you a small—5–8 mm in diameter—galvanometric mirror, to draw out a thin straight glass rod, to the end of which you will attach with sealing wax a little copper disk 5–6 mm in diameter and 0.1 mm thick. Suspend the whole apparatus on a thin glass thread, which you can easily draw out to the desired thickness (ask Nik. Petr. to show you how this is done). With a period of oscillation of the whole system, for example, of 5 sec., the sensitivity will probably be sufficient. If not, then work with a longer period.

3) Arrange the observations in the following manner: first determine the approximate position of the maximum, mark it, and return constantly to this position of the resonator after each separate reading; in this way you will eliminate fluctuations of the intensity in the Kamerton.

4) Process all your observations graphically, i.e., after reducing all observations to a constant deflection at a definite position of the resonator, plot them on coordinate paper and connect them by a smooth curve*).

5) For simplicity, during the observations set not to a definite length of the resonator according to the scale, but simply—

) In the margin is written: “Calculate from the readings according to the graph—this is more accurate than from individual observations.” (Editor’s note.*)

by the numbers of revolutions of the handle of the support: rapid tracking of individual observations considerably increases their accuracy.

6) In making the calculation, bear in mind that with Leibergh the reading of the manometer was directly proportional to the amplitude; with you, with the Rayleigh disk, the deflections are directly proportional to the squares of the amplitudes!

7) In the calculation avoid needless precision and a needlessly large number of points taken.

P. Lebedev

Notes

[1] Leaving abroad for treatment, P. K. Lebedev entrusted the supervision of his practical students (Altberg, Zernov, Zlatovratskii, and Romanov) to N. P. Kasterin, at that time a privatdozent of Moscow University. The first of these instructions (to Altberg) is printed in vol. I of Scientific Heritage. (Student Zernov—Vladimir Dmitrievich Zernov, 1878–1938—subsequently professor and rector of Saratov University, and later professor at MIIT. At that time he was working on the topic “Damping of acoustic resonators”; the work remained unpublished, and the topic was replaced by a new one: “Absolute measurement of the force of sound.”)

[2] P. P. Leibergh (1869–1938) was P. N. Lebedev’s first student in time, who under his direction did work on the damping of acoustic resonators (Journal of the Russian Physico-Chemical Society, physical section, 18, 1896). There is a detailed abstract of it by P. N. Lebedev in the Beiblätter for the same year, 1896.

[3] Nikolai Petrovich Kasterin, who, as stated, supervised P. N. Lebedev’s practical students in 1901. For Lebedev’s private correspondence on this matter see: Scientific Heritage, vol. I, pp. 571, 580, 582, 587, 589.

T. K.