shall not enter; the other (No. 11) on some curious facts respecting the walrus and seal discovered by the examination of specimens brought to England by the polar ships. These facts consist in the peculiarities of structure of the hind flipper, or foot of the walrus, the structure of the stomach, and of the placenta. The former of these alone we consider as of general interest. In a former part of the transactions, Sir E. Home had ascertained the peculiarity of structure in the foot of the common fly, as well as of some species of lizards, by which they are enabled to walk and support themselves in positions opposite to gravity, as on a ceiling, or on a smooth perpendicular glass. This structure consisted in certain folds on the under surface of the foot, which the animal has the power of expanding, so as to produce a vacuum in the cells or cavities formed between them, when the foot is placed against any surface. By this means the weight of the animal is supported against gravity by the pressure of the air. Precisely the same structure was now found in the hind foot or fin of the walrus. By this means it is enabled to hold itself firmly against the smooth surface of the blocks of ice in the polar seas. The anatomical structure of the muscles and tendons by which this power is given, closely resembles that of the corresponding parts in the human hand, which, if enveloped in an elastic covering extending beyond the ends of the fingers, might be used in a similar way. P. 235, &c.

In a short paper (No. 18), Mr. Tredgold has given a set of very neat experiments on the elasticity of steel, from which he infers, that its elastic force is sensibly the same at all states of temper. He conceives his results to agree very closely with the explanation given by Dr. Young of the hardening of steel:

"After a piece of steel has been raised to a proper temperature, a cooling fluid is applied, capable of abstracting beat more rapidly from the surface than it can be supplied from the internal parts of the steel. Whence the contraction of the su perficial parts round the central ones, which are expanded by heat, and the contraction of the central parts in cooling, while they are extended into a larger space than they require at a lower temperature, produces that uniform state of tension, which diminishes so much the cohesive force in hard steel. The increase of bulk by hardening agrees with this explanation; and it leads one to expect, that any other metal might be hardened, if we could find a means of abstracting heat with greater velocity than its conducting power." P. 359.

Captain Sabine, assisted by Lieutenant Forster, during their visit to Spitzbergen, in the summer of 1823, made some observations, partly for the purpose of verifying the heights of certain hills on that coast, and partly for that of comparing the barometrical with the geometrical method of determining elevations. With respect to the former object, they found the chart, as well as the elevations of the hills, laid down by Capt. Phipps, extremely incorrect. The accordance between the determinations of an elevation measured with the greatest possible care, and with the best instruments, was found to be very close. It appears to Captain Sabine, that the erroneous statement of the height of the hill in Captain

Phipps's delineation, must have been an error in the insertion, rather than in the observations. "The genuine record," he observes, "might now have furnished materials, interesting perhaps in a geological point of view, of tracing how much, or possibly how little, diminution in height the naked and pointed summits of the Spitzbergen hills have sustained in the lapse of half a century, and in a climate which is considered as peculiarly destructive." (No. 16, see page 308, &c.)

The velocity with which sound travels through the atmosphere was a point investigated by several philosophers in the early periods of modern science. Newton gave the theory of its propagation, and expressed its velocity by a formula. Actual experiments however, on this velocity, instituted in various countries, went to prove the velocity as found by observation, about one-sixth greater than can be deduced by theory. This difference was accounted for by La Place, on the supposition that heat is evolved by the compression of the particles of air by the undulations. To determine the quantity of heat thus generated was found impossible; empirical corrections were therefore of necessity resorted to; and the accuracy to which this can be done must depend upon the accuracy of the experiments; hence the advantage of repeating them with greater attention to precision. One of the greatest improvements made in the mode of performing operations of this kind, was the plan of observing at two stations the interval between the appearance of the flash and the hearing of the report of guns fired simultaneously at each. Thus the effect of wind in altering the interval was annihilated, the one result being increased by the same quantity as the other was diminished.

This precaution was not adopted till the experiments of the French Academicians were made, in 1822, at the suggestion of M. La Place. In 1823, at the proposal of his royal Highness Prince Frederick, Master General of the Ordnance to the King of the Netherlands, the officers of the artillery, together with Professors Moll and Van Beck, undertook a most elaborate series of observations in Holland. (The full account of their operations and results is given in the volume before us, No. 23, p. 424, &c.) A vast number of precautions not used in former experiments were adopted. The state of the atmosphere, in all its affections, was carefully observed at each station with the best instruments, and the distances of the stations accurately determined by trigonometrical measurement. Of the various details we shall not attempt any description, but shall merely state, that the various results were carefully corrected for the state of the atmosphere, and compared with theory, and with previous determinations. The greatest attention was bestowed on having the shots rigidly simultaneous, by means of accurate time-keepers at each station. The place selected was an extensive heath in the province of Utrecht, and the stations were small hills distinctly visible from each other, at about 2 miles distant, the one named Kooltjezberg, the other Zevenboompjes.

The general result from all the experiments was, that sound travels at the rate of 1089.7445 English feet per second, at 32° Fahrenheit. This result agrees nearly with that of the French philosophers, which is rather greater, as also that of Flamstead, Halley, &c. An extensive comparison of all former determinations, is given at the end of the paper.

On a former occasion we laid before our readers some account of Sir H. Davy's researches relative to the preservation of copper from oxidation, by the contact of more oxidable metals. In the volume of the Transactions now before us, we have a short paper, (No. 12,) from the same author, describing some further investigations on the same subject. He tried several experiments with the view of ascertaining the proportion of protecting metal which might be most advantageous; hammered iron was compared with cast, and he found that the latter, which is the cheapest and most easily procured, is likewise best suited to the purpose; it lasts longer than any other protector, and the plumbaginous substance which is formed after the action of sea water upon it retains the original form of the iron, and does not impede the electrical action of the remaining metal.

It would naturally follow, as a consequence of the theory upon which the process was deduced, that in many cases there would be a deposition of alkaline substances upon the negatively electrical copper; this Sir H. Davy found actually took place. Some sheets of copper having been exposed nearly four months to the action of sea water, and defended by from to of their surface of zinc and iron, became coated with a white matter, which on analysis, was found to be principally carbonate of lime, and carbonate and hydrate of magnesia. Copper on vessels, defended to this extent, on becoming thus coated, became also covered with weeds, insects, &c. When the protection was diminished to below of the surface, the electrical power of the copper being less negative, more neutralized, and nearly in equilibrio with that of the menstruum, no such deposition or adherence of weeds, took place; the surface was slightly corroded, but not to such a degree as to be at all injurious. This experiment is of great practical importance, as pointing out the exact limits to be adopted in defending the coppering of ships. Sir H. Davy considers the wear of cast iron from the oxidation to be not so great, but that a mass of two or three inches in thickness will last for some years; this, he thinks, however, will depend in some measure upon other circumstances, such as the saltness of the sca, and perhaps the rapidity of the ship's motion. It was with the view of ascertaining the effect of this last circumstance, that the author has since made a voyage in a steam-boat across the German ocean, and we understand, found that the utmost velocity of the vessel made no difference whatever in the protecting power of the iron.

But in carrying on these researches, our author has not confined himself to the particular application, important as it is, which has

now been mentioned: he has extended the principle to several other objects. Of these the account he has given in the conclusion of the paper is but short, and we cannot do better than extract it.

"Weak solutions of salt act strongly upon copper; strong ones, as brine, do not affect it; and the reason seems to be, that they contain little or no atmospheric air, the oxygen of which seems necessary to give the electro-positive principle of change to menstrua of this class. I had anticipated the result of this experiment, and upon the same principle, of some others.

"Alkaline solutions, for instance, impede or prevent the action of sea-water on copper; having in themselves the positive electrical energy, which renders the copper negative. Lime water, even, in this way, renders null the power of action of copper on sea-water.

"The tendency of electrical and chemical action being always to produce an equilibrium in the electrical powers, the agency of all combinations formed of metals and fluids is to occasion decomposition, in such an order, that alkaline, metallic, and inflammable matters are determined to the negative part of the combination, and chlorine, iodine, oxygene and acid matters to the positive part. I have shown in the Bakerian lecture for 1806, that this holds good in the voltaic battery. The same law applies to these feebler combinations. If copper in contact with cast-iron be placed in a vessel half full of sea-water, and having its surface partially above that of the water, it will become coated with carbonate of lime, carbonate of magnesia, and carbonate of soda; and the carbonate of soda will gradually accumulate, till the whole surface in the air is covered with its crystals: and if the iron is in one vessel, and the copper forming the arc with it in another; and a third vessel of sea-water in electrical connexion by asbestos, or cotton, is intermediate, the water in this intermediate vessel continually becomes less saline; and undoubtedly by a continuance of the process might be rendered fresh." Phil. Trans. 1824, 2, 246.

We should add, that in a note, the author mentions, that he is at present engaged in applying the principle of the experiment just described on alkaline solutions, to the preservation of animal and vegetable substances. Also, that scientific artist, Mr. Pepys, has ingeniously applied the protecting principle by inclosing finely cutting instruments in handles, on cases lined with zinc.

Several years have now elapsed since the president of the Royal Society in the further prosecution of those researches on flame, which had already led him to the most important practical results, discovered some new and curious phenomena in the combustion of mixed gases, by means of fine wires of platinum, introduced into them at a temperature below ignition. A wire of this sort being heated much below the point of visible redness, and immersed in a mixture of coal gas and oxygen gas in due proportions, immediately became white hot, and continued to glow until all that was inflammable in the mixture was consumed. The wire, repeatedly taken out of the mixture and suffered to cool below the point of redness, instantly recovered its temperature on being again plunged into the mixed gases. The same phenomena were produced in mixtures of oxygen with olefiant gas, with carbonic oxide, with cyanogen, and with hydrogen; and in the last case there was an evident production of water. When the wire was very fine, and the gases had been mixed in explosive proportions, the heat of the wire became sufficiently intense to cause them to detonate. In mixtures which were non-explosive from the redundancy of one or

the other gas, the combination of their bases went on silently, and the same chemical compounds were formed as by their rapid combustion. For the accounts of these researches, we refer our readers to the Phil. Trans. 1817, Part I.

In the autumn of 1823, results of a nature closely analogous in some respects were announced by Professor Dobereiner of Jena, with this striking additional circumstance, that when platinum in a spongy form, is introduced into an explosive mixture of oxygen and hydrogen, the metal, even though its temperature had not been previously raised, immediately glows, and causes the union of the two gases to take place, sometimes silently, at others with detonation. It is remarkable, however, that platinum in this form, though so active on mixtures of oxygen and hydrogen, produces no effect, at common temperatures, on mixtures of oxygen with those compound gases which were found by Sir H. Davy to be so readily acted upon by the heated wire. One gas, carbonic oxide, indeed appears from the statements of M.M. Dulong and Thenard, to be capable of uniting with oxygen, at the temperature of the atmosphere, by means of the spongy platinum; but Dr. Henry in repeating the experiment, found, that though this is in strictness true, yet the combination was so extremely slow, that the due diminution of volume was not completed till several days had elapsed. And on mixtures of olefiànt gas, of carburetted hydrogen, or of cyanogen, with oxygen, the sponge does not, by any duration of contact, exert the smallest action at common temperatures.

It was this inefficiency of the platinum sponge on the compounds of charcoal and hydrogen, in mixture with oxygen, while it acts so remarkably on common hydrogen, and also, though slowly on carbonic oxide, that suggested to Dr. Henry the possibility of solving by its means some interesting problems in the analysis of gaseous bodies; he hoped more especially to be able to separate from each other the gases constituting certain mixtures, to the compositions of which approximations only had been made, by comparing the phenomena and results of their combustion, with those which ought to ensue, supposing such mixtures to consist of certain hypothetical proportions of known gases. For instance, it might be expected that, from a mixture of hydrogen and carburetted hydrogen with oxygen, the platinum sponge would cause the removal of the hydrogen, leaving the carburetted hydrogen unaltered. To ascertain this, and a variety of similar points, he made artificial mixtures of the combustible gases in known volumes, and submitted them, mixed with oxygen, sometimes to contact with the sponge, and sometimes with balls made of clay, and platinum; a method also used by Professor Dobereiner, the sponge being mixed into a paste with fine clay, and then formed into small balls, by which means it is readily passed up into a gaseous mixture, through the mercury in the pneumatic trough. Dr. Henry's paper is of considerable length, and is so full of curious facts, that it is hardly possible to abridge it. Various mixtures of nearly all the gases formed