when they overspread the earth at a moderate elevation, seems to accommodate itself to all the variations of form in the subjacent soil." Mr. Green has also found, that it is usual to ascend to a greater elevation to experience the same reduction of temperature when the earth is overspread with clouds than in a cloudless sky. According to Mr. Monck Mason, a singular relation is found to exist between the formation or precipitation of rain, and the condition of the sky above the clouds which contain it. "Whenever from a sky completely overcast with clouds rain is falling, a similar range of clouds invariably exists in a certain elevation above, whereby the rays of the sun are intercepted from the layer below; and on the contrary, whenever, with the same apparent condition of the sky below, rain is altogether or generally absent, a clear expanse of firmament, with a sun unobstructed by clouds, is the prevailing character of the space immediately above: thus leaving it a determinate fact, that when rain is pouring from clouds overspreading the earth, the rays of the sun are not operating upon the clouds in question; while, on the other hand, rain does not fall from such clouds when the rays of the sun are unobstructedly falling upon the upper surface." According to the same authority, and in conformity with the opinion of Mr. Green, it appears that, in this country, whatever may be the direction of the wind below, in the higher regions, that is, generally within 10,000 feet above the surface of the earth, the direction of the wind is invariably from some point between the north and west. It appears from Mr. Green's observations, that "the variation experienced in the course of the wind during the progress of the ascent was accompanied by a corresponding alteration in the intensity of its rate, the current which at the commencement was gentle becoming strong as it took another direction, and vice versa." These important facts in Meteorology could not have been ascertained by any observations made at the surface of the earth, and afford strong evidence of the advantages which might result to science from well-planned aeronautic expeditions. With regard to the atmosphere of vapour, it is probable that it tends to the maintenance of an analogous but very different progression of density and temperature, from below upwards, to that of the gaseous atmosphere; but being constrained to diffuse itself through the latter, it is controlled and regulated by the temperature into which it is thus forced. Thus the elasticity with which it will rise from the surface of the earth, in the act of evaporation, will be determined by the temperature of some upper stratum of the air, at which it will become condensed, the force at which point will limit by its reaction that of the evaporating surface. Between these two points, therefore, the dew-point will probably be found to be steady, or to decline by a very slow progression. After passing through the cloud, it may be expected that the dew-point will fall at once several degrees; the elasticity of the vapour on the upper side being probably governed and determined by a new point of condensation in still higher regions, just as the dew-point on the surface of the earth is conceived to be determined by the temperature of the first vapour-plane. This would imply, that while precipitation was taking place on one side of a bed of clouds, rapid evaporation might be going on upon the other. It is also conceivable that these processes of condensation and evaporation may be so adjusted as that they may exactly counteract each other; and the vapour-plane might thus be indicated by no cloud, or possibly by a mere haze; but the dew-point would fall suddenly. To this circumstance the observer's attention should be particularly directed. It is probable that, in ascending to a great height, several vapour-planes might be thus crossed, and the confirmation of the hypothesis would be of importance to science in elucidating the constitution of the atmosphere. It is obvious that,

for the purposes just indicated, the observations of the thermometer and dew-point should, if possible, be unremitted during the whole time both of the ascent and descent, and, of course, must be accompanied by simultaneous observations of the barometer: one person's time should therefore be wholly devoted to these objects; and the arrangement should be well considered, by which his labour may be facilitated and his attention kept undistracted. The prevailing forms and structure of the clouds; their internal motions, if any; the number of strata which may be detected, and the number and direction of the currents which their motion may indicate, will also form interesting objects of observation in conjunction with the preceding. Contemporaneous observations will, of course, be made on the earth during the time of the aërostatic voyage, which will possess a greatly-increased interest if circumstances should permit it to take place on the day when hourly meteorological observations are made at all the principal observatories of Europe, according to the plan laid down by Sir J. Herschel. Portions of the air should be brought down, for examination, from the highest elevations; and this may probably be best effected by taking up several glass balloons, or bottles carefully gauged, fitted with stop-cocks, and filled with water. The water should be allowed to run out at the proper station, and the stop-cocks closed. Experiments upon the radiation of heat, by another observer, would also be interesting, although there are probably no known means of instituting them with all the accuracy which could be desired. Observations with Sir J. Herschel's actinometer might be made upon the force of solar radiation at various heights; but the instrument would not be applicable to the measurement of terrestrial radiation. When a delicate thermometer, whose bulb is covered with lamp-black, is placed in the focus of a parabolic reflector, and turned towards the clear sky, even in the day-time, it will radiate a portion of its heat into space; by the same contrivance, the rays of heat proceeding from the earth, or from beds of clouds, would be condensed upon the thermometer, and some estimate formed of their intensity. Observations upon these points at different heights, and at different periods of the day and night, would be instructive, though not of the high importance which would belong to those of the thermometer and hygrometer. To these observations might be added others of great interest upon the electricity of the atmosphere, by dropping wires into clouds, or from stratum to stratum of cloudless air, and examining the nature of the electricity of their extremity by means of a very delicate electroscope: but attractive as these researches may prove, the Committee recommend, that should a series of ascents be undertaken by one or many observers, on no occasion should the observer's attention be distracted by too great a variety of objects; and that our efforts should at first be directed solely to the elucidation of the question of the decrease of temperature, by the acquisition of accurate contemporaneous observations of the barometer and thermometer made at different elevations. It would manifestly be desirable, that while observations of atmospheric temperature and pressure were made in a balloon, two observers, stationed at the extremities of an accurately measured base, and provided with theodolites of the best construction, should by their observations determine the height of the balloon geometrically, at the instants the observations of temperature and pressure were made. This, however, implies a more extensive system of cooperation, and a larger personal and instrumental force, than could probably be assembled. It will, therefore, be best to confine the observations simply to the determination of corresponding temperatures and pressures of the atmosphere. For this purpose nothing more is wanted than a supply of instruments that can be easily used and give accurate results.

Of the Hygrometer.-It is desirable that two hygrometers should be provided, which may be fixed side by side upon the lid of a box, into which they may be contrived to pack. The observer should not only note the temperature of the first appearance of dew, but the temperature at which it again disappears; and while he is waiting for the last observation by one instrument, he may proceed to make a new one with the other. A store of the best æther should be provided, and a convenient dropping-bottle. No disadvantage would arise from the effect of the diminished pressure upon the boiling-point of the æther, if placed in a bottle contrived for the purpose; as thus, a b the bottle,

a

c d the level of the æther,

ef a tube fitted tight into the neck, and passing to the bottom of d the liquid, furnished with a stop-cock e. As the atmospheric pressure diminished upon the aperture of the stop-cock, the b pressure of the included vapour would pour out a stream of æther, which might be regulated, and the rapidity of its subsequent evaporation would be a great advantage; but as it is probable that the dryness of some of the upper sections of the atmosphere may be extreme, smaller tubes, filled with condensed sulphurous acid, should be provided, and kept cool in ice, by the dropping of which upon the bulb of the hygrometer extreme cold may be produced. As an additional precaution, a small bright silver capsule and delicate spirit-thermometer may be prepared, by which the dew-point may be observed from the direct evaporation of the acid. Bottles containing a mixture of liquid carbonic acid and æther might perhaps be prepared, which would answer the purpose still more perfectly. As it is extremely desirable that the relation of the cold produced by evaporation from the surface of a wet-bulbed thermometer with the dew-point should be ascertained, and as such an observation would not add much to the trouble of the observer, Dr. Mason's hygrometer, which is a convenient form of the instrument, may be fixed upon a stem upon the box, immediately behind the hygrometers, and the temperatures of the two thermometers may be noted. The freezing of the water in the upper regions will, however, put an end to these observations. The stem which supports the thermometers may also be made to carry a moveable card-board, covered on the outside with gilt paper, so as to screen all the instruments from direct radiant heat.

Of the Barometer.-The only barometer that can be used, and can be trusted in observations like those in question, appears to be the Siphon-barometer of Bunten, in Paris (Quay Pelletier, No. 26), or barometers of a similar construction by Robinson, of London. The tubes of Bunten appear to be carefully made; the column of mercury is easily seen; and the slow motion of the verniers, though not so fine as in Robinson's, is more easily managed, a circumstance of some importance in the present instance. The barometers should be new: their scales divided in millimetres only. Some of them have a scale of English inches, which, owing to some mistake about standard temperature, is very erroneous. They should be always kept inverted, except when in actual use. When allowed to hang in the position in which they are used, the mercury in the short tube becomes oxidized, the glass covered with a powder of the oxide, and the capillary depression considerably increased, which renders the instrument useless. In a cisternbarometer, where the level of the mercury cannot be observed, the corrections for a change of level for small variations of barometrical pressure are extremely troublesome. For large changes of barometrical pressure they const become uncertain in the highest degree. Troughton's mode of deterng the lower level is decidedly bad. The cistern-barometers, in which

the lower level is determined by contact of a point with the surface of mercury, are good comparative or differential instruments, but nothing more.

Of the Thermometer.-The best and most convenient thermometers appear to be those made by Greiner, of Berlin, with a paper scale enclosed in an

outer tube, or a scale of milk-white glass. The bulbs are exposed, and the scales cannot be injured by immersing the bulbs, or whole instrument in water, or any other liquid, for purposes of comparison. The graduation should extend from 85° Fahr. to about + 100° Fahr. In Gay-Lussac's ascent, the thermometer descended 40° 25". It is not likely that any observers would ascend much higher than he did, or that they would undertake an ascent when the temperature at the earth's surface was less than 10° C. The thermometers, during the ascent, should be enclosed in bright tin tubes (having an opening through which the scale can be observed), open at both ends, with a round disc of tin at a little distance from the ends, to prevent the effect of radiation. Thermometers thus protected were used at the Cambridge Observatory, and found to answer well. The temperature of the air being already known, one thermometer with a wet bulb will be sufficient to determine the pressure of vapour at a given station.

ه

Directions for Observing.-When the motion of the balloon in a vertical direction appears to be small. 1. Observe the thermometer attached to the barometer. 2. Make the lower edge of the upper ring appear to touch the upper end of the mercurial column. 3. Make the lower edge of the lower ring appear to touch the lower end of column. 4. Observe the thermometer in the tin case for temperature of air, and note the time. 5. Read off the two verniers of the barometer. 6. Observe the psychometer (wet-bulb thermometer) and Daniell's hygrometer. The observations at the surface of the earth should be made in the same order. The observers should avoid as much as possible approaching the thermometer and barometer, in order that they should not influence the temperature. The aëronaut must be instructed in making the contact between the ring and the end of the mercurial column, also in reading a vernier correctly.

Tin cases for thermometers, Daniell's hygrometer, &c.

It would be manifestly imprudent to commence operations with only just a sufficient stock of such fragile instruments as barometers and thermometers. Duplicates of every one should be provided. This would make the cost of the instruments amount to about 50%. To the above might be added,—a sympezometer, constructed for the purpose, without sliding scale,—a maximum and minimum thermometer, about as large as a watch, constructed by Breguet.

(Signed)

DAVID BREWSTER,
J. F. W. HERSCHEL,

J. W. LUBBOCK,

T. R. ROBINSON,

EDWARD SABINE,
W. WHEWELL,
W. H. MILLer.

Report on British Fossil Reptiles. By RICHARD OWEN, Esq., F.R.S., F.G.S., &c. &c.

PART II.

THE British Fossil Reptiles described in the first part of this Report presented modifications of their osseous structure, and especially of the vertebral column and locomotive extremities, by which they were especially adapted for a marine life, and hence have been collectively termed Enaliosauria. All the numerous species of this family are extinct, and it seems that the genera have ceased to be represented since the deposition of the chalk formations. In the present zoological systems the Plesiosauri and Ichthyosauri are referrible to the Saurian order of reptiles, as defined by Cuvier; but they offer the most remarkable deviations from the existing types, and constitute links which connect the Reptiles, on the one hand, with Fishes, and, on the other hand, with the cetaceous Mammals.

The present and concluding part of the Report on British Fossil Reptiles contains an account of the remains of the Crocodilian, Dinosaurian, Lacertian, Pterodactylian, Chelonian, Ophidian and Batrachian reptiles.

The most remarkable of the extinct species of the amphibious and terrestrial Sauria of England have been discovered and described by Dr. Buckland and Dr. Mantell. Some remains are briefly noticed by Parkinson*, and by the older English observers, as Wooller and Chapman. Cuvier has added to the value of these discoveries by his just observations and comparisons. Some of the British Chelonian fossils have been noticed by Parkinson, Cuvier and Dr. Mantell; but none of the British extinct Ophidians or Batrachians appear to have been hitherto recognized as such.

PLIOSAURUS.

The Enaliosaurs are immediately connected with the Crocodilian reptiles by an extinct genus, represented by species of gigantic size, of which the remains are not unfrequent in the Kimmeridge and Oxford clays. The Reptile in question is essentially a modified Plesiosaurus, but its modifications appear to entitle it to be regarded as a distinct genus, which, as it is more closely allied to the true Sauria, I have proposed to call Pliosaurus†.

Large, simple, conical teeth, with the enamelled crown traversed by welldefined and abruptly terminated longitudinal or oblique ridges, as in the teeth of the Plesiosaur, have not unfrequently been discovered in the Kimmeridge clay formation. These teeth differ from those of the Plesiosaur in their greater relative thickness as compared with their length, and in the subtrihedral shape of their crown; the outer side is slightly convex, sometimes nearly flat; it is separated from the two other sides by two sharp ridges; these are more convex, and the angle dividing them is often so rounded off that they form a demi-cone, and the shape of the tooth thus approximates very closely to that of the Mosasaur, with which it is equal in size. It may be readily distinguished, however, even when the crown only is preserved, by the ridges which traverse the inner or convex sides, the outer flattened surface alone being smooth; but an entire tooth of the present extinct Reptile presents a long fang, which at once removes it from the acrodont group of lacertine Saurians, and allies it with the thecodont Reptiles, among which it approaches nearest, in the superficial markings of the crown, to the Plesiosaur.

The known parts of the skeleton of the gigantic extinct reptile, to which the teeth in question belong, confirm this approximation; but the vertebræ of the

* Organic Remains of a Former World, vol. iii.

† Odontography, Part II., p. 282.