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observations; but the bore continues for about 70 feet further. We have here a total increase of 4° in 300 feet, which is at the rate of 1o in 75 feet; but the intermediate steps are so irregular that not much weight can be attached to thiş determination.

The Secretary has corresponded with the Smithsonian Institution respecting the great bore at St. Louis, which was described in last year's Report, and also respecting the Hoosac Tunnel which passes under a mountain and will be 4 miles long, but the correspondence has not yet led to any definite result.

It was stated in last Report that application had been made to General Helmersen, of the Mining College, St. Petersburg, for information regarding the temperature of a very deep bore in course of sinking at Moscow, as well as regarding underground temperatures in Russia generally. A long delay occurred, owing to the General being absent from home for seven months, and not receiving the communication till his return; but shortly after his return he dispatched a very polite answer, from which the following passages are extracted:"We have an artesian well in St. Petersburg, bored in the Lower Silurian strata. At the depth of 656 English feet this well stops at the granite, a granite which perfectly resembles that of Finland. The lowest portion of these Silurian strata is merely a degraded granite, a grit combined with débris of felspar. About 353,000 hectolitres of water flow from the well per diem, and this water issues with a constant temperature of 9°.8 Reaumur. You are doubtless aware of the existence of a series of observations on the temperature of the soil at the bottom of a well which was sunk in the town of Yakoutsk in Eastern Siberia. This well has shown us that the soil of Siberia, at least in this part of its great extent, is frozen to a depth of 540 English feet. The mean temperature of Yakoutsk is -8°.2 R. At the depth of 100 feet the temperature of the soil was found to be -5°.2. From this depth to the bottom the temperature increased at the rate of 1° R. for every 117 feet; whence it would follow that the soil at Yakoutsk is frozen to the depth of about 700 feet.

"It appears to me a very interesting circumstance that, according to accounts just received by the Academy of Sciences from Baron Maydel, traveller in the country of the Tchukchees [des Tschouktschi], there are found in those regions layers of ice, quite pure, alternating with sand and clay. The interesting letter of the Baron will shortly be printed in the publications of the Academy. It was in making excavations in search of mammoths that Maydel made this discovery."

If we assume the temperature of the surface of the soil at St. Petersburg to be 39° 17 F., which, according to Herschel's Meteorology,' is the mean temperature of the air at the Magnetic and Meteorological Observatory, and if we take the temperature of the water as that of the bottom of the well, we have an increase downwards of 14o·88 F. in 656 feet, which is at the rate of 1° F. in 44.1 feet. If, on the other hand, we suppose the surface of the ground to be 4° F. warmer than the air (and the difference at Yakoutsk appears to be greater than this), we deduce an increase at the rate of 1° F. in 60 feet.

The rate of increase at Yakoutsk from the depth of 100 feet to the bottom of the frozen well at 540 feet is given above by General Helmersen as 1° R. in 117 feet. This is 1° F. in 52 feet.

An account of the Yakoutsk well is given in Comptes Rendus,' tome vi. 1838, p. 501, in an extract from a letter by Erman (fils), who visited Yakoutsk when the well had attained a depth of 50 feet. He gives the tem

perature at this depth from his own observations, and the temperatures at 77, 119, and 382 feet from the subsequent observations of the merchant to whom the well belonged. His figures differ very materially from those given above; but it may fairly be presumed that General Helmersen's account is the more accurate.

Before the receipt of General Helmersen's letter, the following communication respecting the Moscow boring had been received by the Secretary from Mons. N. Lubimoff, Professor of Natural Philosophy in the University of Moscow.

"December, 1870.

"DEAR SIR,-I beg your pardon for not having replied sooner to your letter. I am sorry to say that the information which I can now communicate is very deficient. The great bore of Moscow is not yet terminated, and the experiments on temperature which have been made hitherto are but of a preliminary kind. It was in the hope of renewing the measurements under more satisfactory conditions that I delayed my answer; but as certain circumstances did not permit me to resume the observations, which are therefore deferred to the spring of 1871, I must restrict myself to describing the old ones. "These were made, on my commission, by M. Schiller, B.A., in April 1869. The bore was then about 994 feet deep, and, from 56 feet to the bottom, full of water. A mercury thermometer of a peculiar kind was constructed, on an idea of my own. It consisted of a capillary tube of thick glass, terminating below in a large reservoir; at the upper end a funnel-like piece was adjusted, into which the mercury flowed off as soon as the temperature rose above a certain value [sketch annexed]. The whole was placed within a closed case, which was plunged to a chosen depth into the bore, and reversed by means of a special arrangement. It was then brought again to the right position and drawn up to the surface, a portion of mercury having flowed away. Here the thermometer was plunged into a water-bath, the temperature of which was so regulated that the mercury attained the end of the capillary tube; this was then the temperature required.

"The measurements were made at the depths of 175, 350, 525, 700, 875, and 994 feet. From 350 feet to the bottom the temperature throughout the bore was found to be nearly constant, namely 10°-1 C., with deviations of +01. The temperatures of the upper parts of the bore were not quite precisely ascertained, the chief attention being given, in these first experiments, to the deeper parts. The air-temperature at the surface for the time 23 April April to varied between +7o-5 and - 1o·9 C. 5 May


"As soon as the boring is completed, and the present impediments removed from the bore, the observations will be resumed, and perhaps some new methods will be applied for the sake of verification, though the above described apparatus, previously tried, seemed to give very exact results.

"I shall be very glad to communicate to you, as soon as possible, the results of the new experiments. As to underground temperatures for Russia in general, there is, so far as I know, no place where regular and trustworthy observations have been made [should be made in original] except the Central Physical Observatory at St. Petersburg, the results of which are published by Dr. Wild, Director of the establishment, in his printed Annual Reports."

From the sketch annexed to the description in Professor Lubimoff's letter, it appears that the enlargement at the open end of the capillary tube is quite sudden, and not likely to retain any mercury when inverted. The idea of error from this cause may therefore be dismissed; but the instrument is en

tirely unprotected against the pressure of the water in which it is immersed, and it is important to consider what effect this pressure will have.

In thermometers of the ordinary construction this pressure acts only externally, and produces much greater diminution of the internal volume than when, as in Prof. Lubimoff's thermometer, it acts both externally and internally, a mode of action with which we are familiar in the case of Ersted's piezometer.

From Regnault's experiments it appears that the apparent compression of mercury in glass, when the pressure is thus applied, is 000001234 per atmosphere, whereas the apparent expansion of mercury in glass for heat is 0000857 per degree Fahrenheit. The latter number is 69 times the former; it therefore appears that a pressure of 69 atmospheres would be required to falsify the indications of Prof. Lubimoff's thermometer to the extent of 1° F. The actual pressure at the bottom of the well is less than the half of this, and therefore should only produce an error of a few tenths of a degree. This, however, is on the assumption that the glass undergoes no change of figure, a condition which may easily fail of being fulfilled, owing to the want of perfect uniformity in the glass.

Mr. Donaldson has written from Calcutta to the effect that the thermometer which was sent to him has been entrusted to a competent observer, who has taken numerous observations with it, which will be sent shortly.

M. Erman's letter above referred to is immediately followed in the 'Comptes Rendus' by an account, by M. Walferdin, of some observations, which appear to be very reliable, taken in artesian wells in the basin in which Paris is situated. They were taken with maximum thermometers of the kind invented by Walferdin himself, in which the mercury overflows into a reservoir when the temperature exceeds a certain limit, the thermometers being hermetically sealed in glass tubes to protect them from pressure.

The observations which he first describes were taken in a well, newly sunk to the depth of 263 metres, at St. André, about 50 miles to the west of Paris, and which failed to yield a supply of water. The temperature was carefully observed at the depth of 253 metres by means of two thermometers, which were allowed to remain at that depth for ten hours. Their indications agreed to 03 of a degree Centigrade, and gave a mean of 17°.95 C. For the sake of comparison, M. Walferdin observed the temperature at the bottom of a well 75 metres deep, situated at a distance of only 13 metres from the other well, and found it 12°.2C., showing a difference of 5°-75C. in 178 metres, which is at the rate of 1° C. in 30.95 metres, or 1° F. in 56.4 feet. He mentions that he also employed two Six's thermometers (deux thermométrographes) enclosed in copper tubes to protect them from pressure, but both of these gave erroneous indications. The copper case of one was imperfect, and allowed a little water to enter. This one read 10-25 too high, owing probably to the effect of pressure; the other read 2°-15 too low, owing probably to the index being shaken down.

The temperature at the depth of 400 metres in the puits de Grenelle at Paris was observed on two different occasions. The indications were 23°.5 on the first and 23°.75 on the second occasion; and these M. Walferdin compares with the constant temperature 11°.7 in the caves of the Observatory at the depth of 28 metres. Taking the mean of the two observations, 23°.6, we have a difference of 11°.9 in 372 metres, which is at the rate of 1° C. in 31.2 metres, or 1° F. in 56·9 feet.

Observations in the well of the Military School, at a distance of 600 metres from the puits de Grenelle, showed a temperature of 16°-4 C. at the depth of

173 metres. This gives, by comparison with the Observatory caves, an increase at the rate of 1° C. in 30.85 metres, or 1° F. in 56.25 feet.

These three determinations are in wonderfully close agreement with each other. All three wells are sunk in the chalk of the Paris basin. In the case of the St. André well the thicknesses of the different strata were:—

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The thermometer which the Committee have been employing for the last three years is a Phillips's maximum, having so fine a bore that the detached column of mercury which serves as the index is sustained in the vertical position by capillary action, and will bear a moderate amount of shaking without slipping down. Numerous instances, however, have occurred in which the index has slipped in consequence of jerks or concussions sustained by the thermometer in hauling it up from a depth. During the past six months the Secretary has been in correspondence with Messrs. Negretti and Zambra respecting a proposed modification of the maximum thermometer known by their name, which occurred to him more than a year ago, and was described by him privately to some meteorological friends at the last Meeting of the Association. It was then supposd to be new, but it now appears that Messrs. Negretti and Zambra have made something of the kind for the last fourteen or fifteen years. Several changes, however, were necessary before the thermometer was adapted to the uses of the Committee, and the first complete instruments were received in June last. They are enclosed, like the thermometers previously used, in hermetically sealed tubes, for protection against pressure, and they have the advantages (1) of being able to bear more severe jolts without derangement of their indications, and (2) of presenting to view a much broader column of mercury, so as to be more easily read in a dim light.

The instrument is to be used in a vertical position, with the bulb uppermost. Between the bulb and the stem there is a contraction, through which the mercury will not pass except under pressure. It is set by holding it with the bulb end lowest, and tapping this end on the palm of the hand, till the part between the contraction and the bulb is full of mercury. It can then be held with the bulb up, and the mercury in the stem will run down to the lower end, from which the graduations begin. In this position, the top of the column indicates the temperature of setting, which must be lower than the temperature intended to be observed.

The instrument is then to be lowered into the bore to any required depth, and allowed to remain there for about half an hour, to ensure its taking the temperature of the surrounding water. The expansion of the mercury in the bulb with heat will force a portion of the liquid through the contraction, and subsequent cooling in hauling up will not cause any of it to return. The portion which has thus escaped from the bulb into the stem will usually be found remaining close to the contraction, when the thermometer has been hauled up. The instrument must then be gently inclined, so as to make the bulb end slightly the lowest, when the mercury in the stem will all unite into one column, which will run down to its place on again raising the bulb. The head of the column will then indicate the required temperature.

Report on Observations of Luminous Meteors, 1870-71. By a Committee consisting of JAMES GLAISHER, F.R.S., of the Royal Observatory, Greenwich, ROBERT P. GREG, F.R.S., ALEXANDER S. HERSCHEL, F.R.A.S., and CHARLES BROOKE, F.R.S., Secretary to the Meteorological Society.

THE object of the Committee being, as in the previous year, to present a condensed Report of the observations which they have received, and to indicate the progress of Meteoric Astronomy during the interval which has elapsed since their last Report, the reviews of recent publications relating to Meteoric Science which will be found in the sequel are preceded by a statement of the results obtained by the observers, who have during the past year contributed a valuable list of communications on the appearances of luminous meteors and regular observations of star-showers to the Committee. The real heights and velocities of thirteen shooting-stars obtained by the cooperation of Mr. Glaisher's staff of observers at the Royal Observatory, Greenwich, during the simultaneous watch for meteors on the nights of the 5th to 12th of August last, are sufficiently accordant with the real velocity of the Perseids (as already previously determined by similar means, in the year 1863) to afford a satisfactory conclusion that the results of direct observation are in very close agreement with those derived from the astronomical theory of the August meteor-stream. Shooting-stars were observed to be more than usually frequent on the nights of the 17th of August and 24th of September last, accompanying on the latter night a rather brilliant display of the Aurora. On the nights of the 18th-20th of October last the sky was so generally overcast as to conceal the view of any meteoric shower which may have taken place on that well-established meteoric date. But on the mornings of 13th-15th of November last a satisfactory series of observations of the November star-shower (so far as its return could be identified) recorded at the Royal Observatory, Greenwich, and at several other British stations, concurs with very similar descriptions of its appearance in the United States of America in showing the rapid decrease of intensity of this display since the period of greatest brightness, which it attained in the years 1866 and 1867. Notices of the extreme brightness with which it was visible in the following year (1868) are extracted from astronomical and meteorological journals kept in Switzerland and Scotland. A short view of the sky on the night of the 12th of December last was obtained at Birmingham, where the accurate divergence of the meteors observed by Mr. Wood from the radiant point in Gemini of the December meteors sufficed to verify the periodical return of that meteoric current. The state of the sky was not favourable for observations of meteors on the first two nights of January; but during two hours, when the sky was clear, on the night of the 20th of April last, the well-known group of April meteors was noted, on the periodical date, diverging in considerable numbers, and with the characteristic features of brightness, and leaving a persistent streak from the direction of a nearly fixed. centre in the constellation Lyra. One meteor of the shower, simultaneously observed at Birmingham and Bury St. Edmunds, afforded sufficiently accurate materials for calculating its real distance from the observers, and the length and velocity of its visible flight relatively to the earth. The combined observations of the regularly recurring meteor-showers during the past year having at present proved successful in contributing some valuable materials to their history, the Committee propose to resume during the coming year a systematic watch for their return, and to provide observers

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