V. D. Dudetskii and I. I. Sidorov.

Determination of the Magnetic Elements in the Barnaul and Biisk Districts in 1910 (author’s abstract)

When B. P. Weinberg’s expedition to the Altai glaciers was being equipped in 1910, it was decided to carry out magnetic observations in the mountainous localities of Altai. During the time that was at our disposal (June 6—September 1), the tasks of the expedition required us to travel over a very large area; and, since magnetic observations were not the main purpose of the expedition, it had been decided in advance to make them only at places where stops were necessary, reducing as much as possible the time spent on carrying them out.

The following route was finally adopted: by steamer from Tomsk to Biisk; along the Uimon road from Biisk to Uimon via Anos and Ust-Kan; by pack route from Uimon to Belukha and further via Argut, Dzhelo and Taldura to Kosh-Agach; and, finally, along the Chuya road to Biisk. Thus the survey covered about \(5^\circ\) in longitude and the same amount in latitude.

We had the following instruments at our disposal:
1. Wild’s magnetic theodolite (described in detail by D. A. Smirnovyi in Proceedings of the Academy of Sciences for 1906). We introduced certain changes into the construction of the instrument, concerning chiefly the determination of the horizontal force. 2. An aneroid. 3. A hypsothermometer. All these instruments belong to Tomsk University. 4. Two Ericsson table chronometers (Nos. 85 and 119). The latter was left in Barnaul at the disposal of the postal official Bauer, who agreed to undertake the work of comparing chronometer 119 with our traveling one by telegraph.

Work en route was usually conducted in the following order. I. I. Sidorov determined, from the sun, the correction of the chronometer and the azimuth of the reference mark, and took readings of the magnetic meridian. After this V. D. Dudetskii made observations of the oscillations of the magnet and, at certain points, determined the declination. Finally, the inductor was placed in the position of the little house with the magnet, and the inclination was determined. In some cases (absence of sun, etc.) the usual order was changed. When one person made observations, the other kept the record. About \(1 \tfrac{1}{2}\) hours were spent at each point, including the setting up and packing of the instruments. We used a tent only in case of unfavorable weather; in good weather we simply screened the instrument from the sun with a piece of canvas.

For the determination of the chronometer correction, the moments when the upper and lower limbs of the sun touched one of the horizontal threads of the telescope were usually noted, with the circle left and the circle right, and both verniers of the vertical circle and the level attached to it were read. The chronometer was transported in a box stuffed with hay. The impossibility, under the conditions of travel, of taking greater precautions had its effect, as comparisons with Barnaul by telegraph at five points showed, in irregularities in the rate of the chronometer; therefore, in processing the results, we could not use chronometer corrections to correct the longitudes taken from maps. But, since at each point the correction of the chronometer to local time was determined, these irregularities had no substantial significance in finding the geographical me—

of the meridian, and, consequently, of the magnetic declination from our observations. For the determination of the geographic coordinates we had at our disposal: 1. Lists of astronomical points (18 cases), 2. a map of the General Staff, and 3. a map of the Altai district. All these sources give large discrepancies, reaching up to \(20'\) in latitude and \(10'\) in longitude. A comparison of the chronometer corrections with the differences of longitudes at reliable points gives us a mean observational error of \(\pm 5\) seconds, explained by the irregularity of the chronometer’s rate while en route.

In determining the declination, in some cases we first determined separately, after measuring the altitudes of the sun, the azimuth of some mark by two pointings with the circle to the right and to the left; in other cases (the second half of the journey), simultaneously with the reading of the vertical circle, the horizontal circle was also read; the pointing in such cases was made at the sun so that the vertical thread divided the solar disk in half. Often no pointing at a mark was made, and we confined ourselves to reading the horizontal circle. The computations were carried out by the usual formulae. Four pointings at the magnet were made. Unwinding was performed only at 8 points. The expenditure of time connected with reversing the magnet often compelled us to be satisfied with two repeated pointings at the magnet, subsequently introducing a correction for collimation, which was taken as equal to \(-38'7\) for the southern end of the magnet and \(+27'0\) for the northern. The accuracy of the determination of declination was governed by the error in determining the astronomical meridian, which, under unfavorable conditions depending on the inaccuracy of the latitude and the position of the sun, could amount to \(5'\), while under more favorable conditions it did not exceed \(2'—3'\).

The Wild instrument, being a relative instrument, requires, for the determination of horizontal intensity, a preliminary comparison with a constant instrument of some observatory. Not having the possibility of making a comparison of the instrument before the journey, and wishing not to depend on the variability of the instrument, we introduced into the construction of the instrument a modification consisting in the fact that rulers were made for the instrument, on which the magnet is placed during deflections. This made it possible to produce deflections at two distances and, by determining the constants of the instrument, to judge its variability.

For the constants of the instrument the following values were obtained. The conversion factor \(A\), according to the measurements of 1910 in Tomsk, was obtained from the dimensions as 4.2844, and according to the determinations of 1912 proved equal to 4.2750. Comparisons by M. I. Sidorov with the instruments of the Pavlovsk Observatory in 1911 gave \(A = 4.3110\), and those by V. D. Dudetsky with the instruments of the Irkutsk Observatory in 1912 gave \(A = 4.2974\). From this we conclude that \(A\) varies with time and see that the instrument itself diminishes the intensity by approximately \(0.4\%\). In the computations \(A = 4.311\) was adopted. The temperature coefficient \(\mu\) was found to be 0.00073 from determinations in Tomsk, Pavlovsk, and Irkutsk; according to Prof. Kaustin’s data \(\mu = 0.00072\), and according to Smirnov \(\mu = 0.00066\). Taking into account the relative weights of all determinations, we finally took \(\mu = 0.00068\).

The inclination was determined by the inductor attached to the Wild theodolite. Only two readings were made: with circle E and with circle W.

For the purpose of judging the diurnal and periodic variations of terrestrial magnetism, a temporary magnetic station was organized in Anos. A comparison of its readings with those of Irkutsk shows that the daily course is similar at both stations, but at Anos the amplitude of the declination is somewhat greater than at Irkutsk. The results of the observations are reduced to the mean for June, July, and August.