Here a subterranean stratum of ice was pierced to a depth of more than 382 feet. The thermometer was sunk at eleven points along the lateral walls of the shaft between the surface and the greatest depth, which was reached in 1837. The observer was obliged to be let down standing in a bucket, with one arm fastened to a rope, while he read off the thermometric scale. The series of observations, whose mean error does not amount to more than 0°.45 F. embrace the interval between April 1844 and June 1846. The decrease of cold was not proportional to the depth at individual points, but nevertheless the following results were obtained for the total increase of the mean temperatures for the different superimposed frozen strata :

After a very careful consideration of all these observations, Middendorff determined the general increase of temperature to be 1° F. for every space varying from 44°.5 to 52 feet.46 This result shows a more rapid increase of heat in

to continue the boring; and, up to 1837, although an opening had been made to a depth of 382 feet below the surface, it had not penetrated beyond the ice.

"If we exclude,"

46 Middendorff, Reise in Sib. Bd. i, s. 125-133. says Middendorff, "those depths which did not quite reach 100 feet, on the ground that they were influenced by annual deviations of temperature, as was determined by experiments previously made in Siberia, we shall still find certain anomalies in the partial increase of heat. Thus, for instance, between the depths of 150-200 feet the temperature rises at a ratio of 1° F. for only 29.3 feet, while between 250300 feet the corresponding increase is 96.4 feet. We may, therefore, venture to assert that the results of observations that have hitherto been obtained in Shergin's shaft are by no means sufficient to determine with certainty the amount of the increase of temperature, and that, notwithstanding the great variations which may depend upon the different conductive powers of the terrestrial strata, and the disturbing influence of the air or water which enters from above, an increase of 1° F. occurs for every 44-52 feet. The result of 52 feet is the mean of six partial increases of temperature, measured at intervals of 50 feet between the depths of 100 and 382 feet. On comparing the mean

Schergin's shaft than has been obtained from different borings in Central Europe, whose results approximate closely to one another (see p. 37). The difference fluctuates between 4th and 4th. The mean annual temperature of Jakutsk was determined at 13°.7 F. The oscillation between the summer and winter temperature is so great, according to Newerow's observations, which were continued for fifteen years (from 1829 to 1844), that sometimes for fourteen days consecutively in July and August, the atmospheric temperature rises as high as 77,° or even 84°.6 F., while during 120 consecutive winter days from November to February, the cold falls to between -42°.3 F. and -69° F. In estimating the increase of temperature which was found on boring through the frozen soil, we must take into account the depth below the annual temperature of Jakutsk 13°.71 F. with that which was found from observation to be the mean temperature of the ice (26°.6) at the greatest depth of the mine (382 feet), I find 29.6 feet for every increase of 1° F. A comparison of the temperature at the deepest part with that at a depth of 100 feet would give 44.4 feet for this increase. From the acute investigations of Middendorff and Peters in reference to the velocity of transmission of changes of atmospheric temperature, including the maxima of cold and heat (Middend. s. 133–157, 168-175), it follows that in the different borings which do not exceed the inconsiderable depth of from 8 to 20 feet, "the temperature rises from March to October, and falls from November to April, because the spring and autumn are the seasons of the year in which the changes of atmospheric temperature are most considerable" (s. 142-145). Even carefully covered mines in Northern Siberia become gradually cooled, in consequence of the walls of the shafts having been for years in contact with the air; this cause, however, has only made the temperature fall about 1° F. in Schergin's shaft, in the course of eighteen years. A remarkable and hitherto unexplained phenomenon, which has also presented itself in the Schergin shaft, is the warmth occasionally observed in the winter, although only at the lowest strata, without any appreciable influence from without (s. 156-178). It seems still more striking to me, that in the borings at Wedensk, on the Pasina, when the atmospheric temperature is 31° F. it should be 26°.-4 at the inconsiderable depth of 5 or 10 feet! The isogeothermal lines, whose direction was first pointed out by Kupffer, in his admirable investigations (Cosmos, vol. i, p. 216) will long continue to present problems that we are unable to solve. The solution of these problems is more especially difficult in those cases in which the complete perforation of the frozen soil is a work of considerable time; we can, however, no longer regard the frozen soil at Jakutsk as a merely local phenomenon, which, in accordance with Slobin's view, is produced by the terrestrial strata deposited from water (Middend. s. 167).

surface at which the ice exhibits the temperature of 32° F., and which is consequently the nearest to the lower limit of the frozen soil; according to Middendorff's results which entirely agree with those that had been obtained much earlier by Erman, this point was found in Schergin's shaft to be 652, or 684 feet below the surface. It would appear, however, from the increase of temperature which was observed in the mines of Mangan, Shilow and Dawydow, which are situated at about three or four miles from Irkutsk, in the chain of hills on the left bank of the Lena, and which are scarcely more than 60 feet in depth, that the normal stratum of perpetual frost seems to be situated at 320 feet below the surface." Is this inequality only apparent in cousequence of the uncertainty which attaches to a numerical determination, based on so inconsiderable a depth, and does the increase of temperature obey different laws at different times? Is it certain that if we were to make a horizontal section of several hundred fathoms from the deepest part of Schergin's shaft into the adjoining country, we should find in every direction and at every distance from the mine frozen soil, in which the thermometer would indicate a temperature of 4°.5 below the freezing point?

Schrenk has examined the frozen soil in 67° 30′ N. L. in the country of the Samojedes. In the neighbourhood of Pustojenskoy Gorodok, fire is employed to facilitate the sinking of wells, and in the middle of summer ice was found at only 5 feet below the surface. This stratum could be traced for nearly 70 feet, when the works were suddenly stopped. The inhabitants were able to sledge over the neighbouring lake of Usteje throughout the whole of the summer of 1813.48 During my Siberian expedition with Ehrenberg and Gustav Rose, we caused a boring to be made

47 Middendorff, Bd. i, s. 160, 164, 179. In these numerical data and conjectures regarding the thickness of the frozen soil, it is assumed that the temperature increases in arithmetical progression with the depth. Whether a retardation of this increase occurs in greater depths is theoretically uncertain, and hence there is no use in entering upon deceptive calculations regarding the temperature of the centre of the earth in the fused heterogeneous rocky masses which give rise to

currents.

48 Schrenk's Reise durch die Tundern der Samojeden, 1848, Th. i, s. 597.

in a piece of turfy ground near Bogoslowsk (59° 44′ N. L.) among the Ural Mountains on the road to the Turjin mines.49 We found pieces of ice at the depth of 5 feet, which were embedded, breccia-like, in the frozen ground, below which began a stratum of thick ice which we had not penetrated at the depth of 10 feet.

The geographical extension of the frozen ground, that is to say, the limits within which ice and frozen earth are found at a certain depth, even in the month of August, and consequently throughout the whole year, in the most northern parts of the Scandinavian peninsula, as far east as the coasts of Asia, depends, according to Middendorff's acute observations (like all geothermal relations) more upon local influences than upon the temperature of the atmosphere. The influence of the latter is on the whole, no doubt, stronger than any other, but the isogeothermal lines are not, as Kupffer has remarked, parallel in their convex and concave curves to climatic isothermal lines, which are determined by the means of the atmospheric temperature. The infiltration of liquid vapours deposited by the air, the rising of thermal springs from a depth, and the varying conductive powers of the soil, appear to be especially active." "On the most northern point of the European continent, in Finmark, between the high latitudes of 70° and 71°, there is as yet no continuous tract of frozen soil. To the eastward, impinging upon the valley of the Obi, 5° south of the North Cape, we find frozen ground at Obdorsk and Beresow. To the east and south-east of this point, the cold of the soil increases, excepting at Tobolsk on the Irtisch, where the temperature of the soil is colder than at Witimsk, in the valley of the Lena, which lies 1° farther north. Turuchansk (65° 54′ N. L.) on the Jenisei, is situated upon an unfrozen soil, although it is close to the limits of the ice. The soil at Amginsk, south-east of Jakutsk, presents as low a temperature as that of Obdorsk, which lies 5° farther north; the same being the case with Oleminsk on the Jenisei. From the Obi to the latter river the curve formed by the limits of the

49 Gustav Rose, Reise nach. dem Ural, Bd. i, s. 428.

50 Compare my friend, G. von Helmersen's experiments on the relative conductive powers of different kinds of rocks (Mém. de l'Académie de St. Pétersbourg: Mélanges Physiques et Chimiques, 1851, p. 32).

frozen soil seems to rise a couple of degrees farther north, after which it intersects, as it turns southward, the Lena valley, almost 8° south of the Jenessei. Farther eastward, this line again rises in a northerly direction." Kupffer, who has visited the mines of Nertshinsk, draws attention to the fact that independently of the continuous northern mass of frozen soil, the phenomenon occurs in an island-like form in the more southern districts, but in general it is entirely independent of the limits of vegetation, or of the growth of timber.

It is a very considerable advance in our knowledge, when we are able gradually to arrive at general and sound cosmical views of the relations of temperature of our earth in the northern portions of the old continent; and to recognise the fact that under different meridians the limits of the frozen soil as well as those of the mean annual temperature, and of the growth of trees, are situated at very different latitudes; whence it is obvious that continuous currents of heat must be generated in the interior of our planet. Franklin found in the north-west part of America that the ground was frozen even in the middle of August at a depth of 16 inches, while Richardson observed upon a more eastern point of the coast in 71° 12′ lat. that the ice-stratum was thawed in July as low as 3 feet beneath the herb-covered surface. Would that scientific travellers would afford us more general information regarding the geothermal relations in this part of the earth and in the southern hemisphere! An insight into the connection of phenomena is the most certain means of leading us to the causes of apparently involved anomalies, and to the comprehension of that which we are apt too hastily to regard as at variance with normal laws.

51 Middendorff, Bd. i, s. 166. Compare also s. 179. "The curve representing the commencement of the freezing of the soil in Northern Asia exhibits two convexities, inclining southwards, one on the Obi, which is very inconsiderable, and the other on the Lena, which is much more strongly marked. The limit of the frozen soil passes from Berresow on the Obi, towards Turuchansk on the Jenisei, it then runs between Witimsk and Olekminsk, on the right bank of the Lena, and, ascending northwards, turns to the east."