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india-rubber bags, filled with water, and pressed, not by screwing, but by the weight of the rods, were employed with much satisfaction.

All the methods of plugging employed by Herr Dunker involved the use of the iron rods belonging to the boring-apparatus, and therefore would be inapplicable (except at great expense) after the operation of boring is finished and the apparatus removed.

It seems desirable to contrive, if possible, some plug that can be let down and raised by a wire. In the first report of your Committee, it was suggested that two bags of sand, one above and the other below the thermometer, should be used for this purpose. Bags of sand, however, would be liable to rub off pieces from the sides of the bore, and thus to become jammed in drawing up. Mr. Lebour has devised a plug which will be of small diameter during the processes of lowering and raising, but can be rendered large and made to fit the bore, when at the proper depth, by letting down upon it a sliding weight suspended by a second wire. Sir W. Thomson suggests that a series of india-rubber disks, at a considerable distance apart, will probably be found effectual.

Mr. Boot has continued his observations in the bore which he is making at Swinderby, near Scarle (Lincoln). It has now been carried to the depth of 2000 feet, and is in earthy limestone or calcareous shale, of Carboniferous age. Its diameter in the lower part is only 3 inches. In April last the temperature 78° F. was observed at 1950 feet; and more recently 79° F. was observed at 2000 feet—the water, in each case, having been undisturbed for a month. Supposing these results not to be vitiated by convection, and assuming the mean temperature at the surface to be 50°, we have an increase of 29° in 2000 feet, which is at the rate of 1° in 69 feet.

Mr. Symons has taken a series of observations at the depth of 1000 feet in the Kentish-Town well, with the viow of determining whether the temperature changes. The instrument employed is a very large and delicate Phillips's maximum thermometer. The following is a list of the observations :

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The “ depth indicated” is shown by a measuring wheel or pulley, over which the wire runs by which the thermometer is raised and lowered, as described, with a diagram, in the Report for 1869. The above Table shows that there is always some stretching, real or apparent, in the interval between lowering the thermometer and raising it again. Recent observations, by means of a fixed mark on the wire, have shown that the change is not, in the main, a permanent elongation, but an alternation of length. It is probably due in part to the greater tension which the wire is under in raising than in lowering, a circumstance which will cause a temporary difference of length variable with the rapidity of winding up; also in part to the circumstance that the wire is warmer when it has just left the water than when it is about to be let down. Some portion of the irregularity observed may be due to variations of temperaturo in that part of the well (210 feet) which contains air. The observations, taken as a whole, show that any variations of temperature which occur in this well at the depth of 1000 feet are so small as to be comparable with the almost inevitable errors of observation. The observations will be continued at intervals of six months, with additional precautions, and with an excessively slow (specially constructed) non-registering thermometer, in addition to the maximum thermometer hitherto employed.

Through the kindness of the eminent geologist M. Delesse, of the Ecole Normale at Paris, observations have been obtained from the coal-mines of Anzin, in the north of France. They were taken under the direction of M. Marsilly, chief engineer of theso mines. Maximum thermometers of the protected Negretti pattern were inserted in holes bored horizontally to the depth of 6 or 7 of a metre in the sides of shafts which were in process of sinking, and in which there was but little circulation of air. A quarter of an hour was allowed to elapse in each case, after the boring of the hole, before the thermometer was inserted and the hole plugged. Four different shafts were tried. Those designated as Nos. I., II., III. were in the mine Chabaud La Tour, and No. IV, was in the mine Renard.

In shaft I. observations were taken at eight different depths, commencing with the temperature 56.10 F. at a depth of 38.5 metres, and ending with 07 3° F. at 200.5 metres.

În shaft II, there were observations at four depths, commencing with 55° at 873 m., and ending with 03.1° at 185 m.

In shaft III. there were observations at three depths, commencing with 56° at 87.8 m., and ending with 621° at 144 m.

These three shafts, all belonging to the same mine, were very wet, and the temperature of the air in them was 11° or 12° C. (52° or 54° F.).

In shaft IV., which was very dry and had an air temperature of about 15° C. (59° F.), observations were taken at six depths, commencing with 703° F. at 21•2 m., and ending with 84° F. at 134:8 m. I'he mean rates of increase deduced from these observations are:

In Shaft 1., 1° F. in 14.4 m., or in 47•2 feet.
, II., ., 11•5 m., , 37.7 ,

III., , 8.65 m, , 284 ,

, IV., „ 8:57 m., „ 28:1 The observer mentions that in shaft II. there was, at a depth of 90 m., a seam of coal in which heat was generated by oxidation; but no such remark is made with respect to any of the other shafts, although it is obvious that some disturbing cause has rendered the temperature in shaft IV. abnormally high. Possibly the heat generated in boring the holes for the thermometers in this shaft (which was dry) has vitiated the observations, the instruments employed being maximum thermometers. Two of the slow non-registering thermometers mentioned in last year's Report have been sent to M. Delesse, to be used for verification.

The slow-action thermometers are constructed on the following plan :The bulb is cylindrical and very strong, and is surrounded by stearine or tallow, which fills up the space between it and a strong glass shield in which the thermometer is inclosed. The shield is not hermetically sealed (uot being intended for protection against pressure), but is stopped at the bottom with a cork, so that the thermometer can be taken out and put in again if desired. Stearine and tallow were selected after trials of several substances, including paraffin-wax, bees’-wax, glue, plaster of Paris, pounded glass, and cotton-wool. The thermometers are inclosed in copper cases lined with india-rubbor. When placed, without these cases, in water differing 10° from their own temperature, they take nearly half a minute to alter by one tenth of a degree.

In concluding this Report, your Committee desire to express their regret at the losses which they have sustained by the deaths of Prof. Phillips, Sir Charles Lyell, and Col. Strange, of whose valuable services they have been deprived within the last three years.

Nitrous Oxide in the Gaseous and Liquid States.

By W. J. JANSSEN. [A communication ordered by the General Committee to be printed in extenso.] The experiments of Faraday on the liquefaction of gases have already proved that gases at the ordinary conditions of pressure and temperature are vapours at a remote stage from their points of condensation. If several gases submitted to great pressure and the cold of the carbonic acid and ether bath did not exhibit any appearance of liquefaction, the cause is probably that Faraday did not obtain a temperature low enough to produce liquefaction. Hence we may conclude that the gaseous and liquid states of matter depend only on the temperature and pressure to which it is exposed. The interesting experiments of Dr. Andrews with carbonic acid (Philosophical Transactions for 1869) not only verified this conclusion, but gave the important result that gases and liquids are distant stages of the same condition of matter, which may pass into one another without breach of continuity. The temperature at which matter, without sudden change of volume or abrupt absorption of heat, passes from the ordinary liquid to the ordinary gaseous state is called by Dr. Andrews the critical point; above that temperature a gas never can be liquefied by pressure, it behaves like a permanent gas; below that temperature it will be liquid or gas, or more exactly liquid or vapour, according to the pressure to which it is exposed. For the details I refer to the above-mentioncd paper.

I have made the same kind of experiments with pitrous oxide, a gas whose physical properties agree much with those of carbonic acid. The apparatus was similar to that used by Dr. Andrews, to whom I am much indebted for the great kindness with which he has afforded me every instruction, and for his invaluable advice abont the use of his apparatus during my stay at Belfast and afterwards.

As my experiments with nitrous oxide presented anomalies which did not occur with carbonic acid, I first made some experiments with the latter gas, in order to try whether they were to be ascribed to observational errors or to the nitrous oxide I used. The results are given in the following Tables, where 8 is the fraction representing the ratio of the volume of the air after and before compression to one another at the temperature t, e the correspond. ing fraction for the carbonic acid at the temperature t', and I the number of volumes which 17,000 volumes of carbonic acid, measured at 0° and 760 millims., would occupy at the temperature and pressure of the observation. The number 17,000 has been taken as unit to compare these Tables with those of Andrews.

Table 1.-Carbonic Acid at 210.45 C.

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These results agree closely with the experiments of Dr. Andrews at the corresponding temperatures, the differences being only 0.2 of an atmosphere. At 21°:47 the gas passed into the liquid state at a pressure of 59.8 atmospheres, whilst its volume had diminished from 17,000 to 162; with Dr. Andrews this pressure amounted to 60.05 atmospheres, and the corresponding volume of the carbonic acid to 160. As the quantity of air in my case was about ato of the entire volume of the gas, the increase of pressure to liquefy the whole after liquefaction had begun, amounted to about 2.4 atmospheres, viz. from 59.81 to 62:18. The critical temperature I found to be 300.87. It will be observed that the pressures are those indicated by the apparent contraction of the air in the air-tube.

In the following Tables s and € have the same meaning as before, but applied to nitrous oxide ; l, however, represents the number of volumes which 1000 volumes of nitrous oxide, measured at 0° and 760 millims., would occupy at the temperature and pressure of the observation. The experiments were made at the temperatures of 25°.15, 320.2, 36o.4, 38o.4, and 430.8, two series below, and three above, the critical point, which was found to vary between 36°:3 and 36o.7. The appearances were the same as with carbonic acid.

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