desired, to keep advancing every year. In nothing is this great truth more strongly exemplified than in the manufacture and working of submarine cables. Every new one is better than that which preceded it. In the Malta and Alexandria cable it was thought that at last true perfection had been attained, but the next one for the Persian Gulf was better still. The Atlantic cable of 1865 was better than that again, the cable of 1866 better still, and this last French cable is likely to be the best of all. The standard of the manufactured value of a cable is judged by what are called its units of resistance. There is always a certain amount of resistance to the passage of the electric current through the conductor, and the more perfect the insulation of the cable the greater that resistance will be. This amount of resistance is measured by the galvanometer, and is counted by millions of units. Thus, a cable which gave a resistance of only one million of units would at once show that it was defective, and by some hidden leakage allowed the current to escape, and so, of course, allowed it to enter the wire faster than it could have done had it been so carefully insulated that all the electricity must have passed along the conductor, and along that only. Bad materials, which absorb the current, will also give rise to a low rate of resistance, and a low rate of resistance is only a scientific term for a bad cable. The Indian Government insisted on the Persian Gulf cable having a uniform standard of resistance of 50,000,000 units, and this pitch of excellence was thought to be almost unattainable, yet it was done, and more than done. The standard for the Atlantic cable of 1865 was then raised to 100,000,000 units, and that, too, was accomplished. In the cable of 1866 the standard of resistance was raised to 150,000,000 units, and now in this French cable the contract standard is that it must have 250,000,000 units of resistance, and no less. Thus the two Atlantic cables have gained so much in insulation since they left the factory that often during last year, it is said, they gave a resistance as high as 4,000,000,000 units.-Abridged from the Times.

WEST INDIA AND PANAMA TELEGRAPH.

WITH this cable it is proposed to make a most important extension of submarine telegraphs, and which will in time become more important still when the Government of Peru has completed the arrangements it is now making for a wire which will connect the West India system by a telegraph of alternate land and sea lines along the whole line of the South-west Pacific coast from Panama to Valparaiso, and thence across La Plata, to Buenos Ayres and Montevideo, whence there is already an almost complete land line along the eastern coast of South America up to Rio de Janeiro. The cable made by this West India Company consists of 2,550 miles of submarine cable with 350 miles of land line. It is difficult to fix the cost per mile at

which the cable will be made, for as it passes through very varying depths of water, in some parts over what may be called shallows, and in no part at a greater depth than 600 fathoms, the cable varies also in its form of manufacture. It is of what may be called the composite kind—that is, very thick where the water is shoal, very light and strong where the sea is deep, and with two lines of intermediate cables for the intermediate depths. This contract has been taken by the India-rubber, Gutta Percha, and Telegraph Works Company, at Silvertown, where the cable, and where every process in the long and elaborate system of manufacture can be seen, from the first twisting of the copper strand at one end of the works to the finished cable running out into the tanks at the other.

Between Cuba and Florida a submarine line has been laid by Sir Charles Bright, which connects the land lines of Cuba with Key West, and thence all over the States, and by the French or the two English submarine Atlantic lines to all parts of Europe. The new line which the West India Company are about to lay will connect these Cuban lines, and therefore the lines of America and Europe, with Jamaica. From Kingston the line takes a north-easterly bend, passing up to Porto Rico, thence to St. Thomas's, and so on down south again, calling at the islands of Gaudaloupe, Martinique, Barbadoes, Tobago, Grenada, and Trinidad. From Trinidad it goes on to the main land of South America, touching at Georgetown, where it is landed, and so on by land to New Amsterdam and Surinam. At all the places we have mentioned there are stations. From Kingston, Jamaica, there is to be a branch line passing straight to the Panama land lines at Aspinwall.

We have said that the cable will be composite in its outward form and weight; that is to say, that its conductor and its insulation will be the same internally. It is only in the strength of the outer covering of wire that it will in some parts be made thicker and heavier than others. Thus, from the many landingplaces at which the cable will touch, there will be an unusual length of these shore ends-at least 100 miles in all. These ends will all be very massive, though not so massive as the shore ends of the present Atlantic Cable, which have an amount of strength not required on the West India line. It is made of a double sheathing of iron wires, the outer one of twelve very powerful galvanised iron wires, or rods we might almost call them, and the inner sheath of fourteen smaller wires. Both the inner and outer sheath are bound round with hemp, soaked afterwards in tar, and both are also coated outside with Clark's compound, which is understood to be one of the best for protecting cables from the injury which is sometimes caused in shallow water by the attacks of submarine animalculæ. These little devastators, however, fortunately never touch the gutta-percha. The intermediate cable is of very much the same strength as the inner sheathing of the shore ends, and is covered in with

twelve strong wires. The strong deep-sea portion is very little less in size than the intermediate, and is very like the first old Atlantic cable, though nearly twice as heavy and certainly more than four times as strong, for it is sheathed with twelve small wires, but all of solid homogeneous iron. It is merely for convenience sake, however, that this part of the line is called deep, for of deep sea in the general modern meaning of the term-that is, 2,000 or 3,000 fathoms-the West India line has none to encounter. The greatest depth along the route is only 600 fathoms, and the greatest single stretch from station to station little more than 600 miles-a mere trifle when we consider what the science of cable-laying has now been brought to. The different sections we have mentioned will be so tapered in their construction as to be reduced at the point of junction to the exact diameter of the smaller part of the section they are next to join with.

The whole process of manufacturing a cable is a most curious series of operations. From the time that the lump of raw gutta-percha enters the works, very much in appearance and fibre like a compressed ball of dried stable manure, till it is shredded, boiled, cleaned, steamed, melted, macerated, mixed, and re-macerated, and pours out pure to be forced through dies round the copper conductor, the visitor never loses sight of it. When the first coat has been given-and in this cable there are three, with a coating of insulation between each-the process of putting on coat after coat is of course all alike. Here, however, the copper conductor is placed in connection with the batteries to detect faults, and on the first sign of loss of insulation the alarm bell rings, and the works are stopped till the cause of leakage is discovered and the part cut out. The minimum standard of resistance of the present cable is fixed at as high as 300,000,000 units, or 50,000,000 units of resistance higher than the last French cable, and 100,000,000 units higher than the standard under which both the English cables were constructed. This raising of the standard of excellence every year shows conclusively how much more perfect the manufacture is becoming, both mechanically and scientifically. Before leaving the works, the West India cable, to avoid all risk, is to be tested in water of 75 degrees up to as high as 500,000,000 units.-Times.

Chemical Science. ́

RECENT PROGRESS OF CHEMICAL SCIENCE.

DR. DEBUS, President of the Chemical Section of the British Association, stated the actual progress to have been so great that it would be impossible within the limits of an address to give even a bare outline of the more important work done during the year. Dr. Debus endeavoured, under these circumstances, to direct attention to the ideas which at present guide chemists in their researches-to place in a clear light the objects they are striving to attain, and to indicate the direction of the scientific thought of our time.

The speaker referred, in the first place, to the molecular arrangement of the atoms of which bodies are composed, and said that the views of chemists relative to the combinations of atoms in molecules, and to the methods of ascertaining this arrangement, have undergone great alterations and received great additions during the last ten or fifteen years. To a consideration of these changes he invited the attention of his audience. Eighteen years ago Professor Williamson read before the members of the Association a remarkable paper which contained the germ of our modern chemical doctrines, and was the cause of many important discoveries. He proposed to regard three large classes of bodies-acids, bases, and salts-from the same point of view, and to compare their chemical properties with those of one single elected substance. For this term of comparison he chose water. The speaker proceeded to say:-Now, water is composed of three atoms- -two of hydrogen and one of oxygen. Williamson showed that all oxygen acids, all oxygen bases, and the salts resulting from a combination of the two, can, like water, be considered to be composed of three parts or radicals, two of the radicals playing the part of the hydrogen atoms in water, and the third that of the atom of oxygen. Potassic hydrate is water which has one of its atoms of hydrogen replaced by an atom of potassium; hydric nitrate is water which has one atom of hydrogen replaced by nitric oxide; and potassic nitrate is water with one of its hydrogen atoms replaced by nitrate oxide and the other by potassium. This speculation, as every chemist knows, is well supported by experiments; it embraces three large classes of bodies which till then had been considered as distinct. Mr. Gerhardt, in 1853, extended Williamson's views by distinguishing two other types of molecular structure, represented respectively by hydrogen and ammonia; and succeeded, by help of the radical theory, in arranging the majority of the then known substances under the one or the other of the three types already mentioned. Like every theory which is in harmony with experience, the above considerations led to results of unex

pected importance; for it soon became apparent that the radicals which thus replace hydrogen in water are not at all of the same chemical value.

Dr. Debus then entered into an elaborate and technical explanation in proof of this statement, and then went on to say :"Thus every year produces results which improve our conceptions of the atomic and molecular constitution of bodies; and as our knowledge improves, new questions suggest themselves and our power over the elements increases. It has already become possible to prepare in the laboratory bodies of a very complex character, and which a few years ago were only found in the bodies of animals or plants. Alizarin, the beautiful compound of the madder root, has been obtained by artificial means in the course of the year by Messrs. Liebermann and Græbe. Results of such a nature render it highly probable that at no distant period it will be in our power to prepare artificially nearly all, if not all, the substances found in plants and animals. Here I must not be misunderstood. Organic structures, such as muscular fibre or the leaves of a tree, the science of chemistry is incapable of producing, but molecules like those found in a leaf or in the stem of a tree will, no doubt, one day be manufactured from their elements. "I must not conclude this address without reference to two or three subjects of great importance. Professor Bunsen of Heidelberg has published a paper on the washing of precipitates. Every one acquainted with practical chemistry knows how much time is often lost in waiting for a liquid to pass through the filter. Bunsen found the rate of filtration nearly proportional to the difference between the pressures on the upper and lower surfaces of the liquid. If, accordingly, the funnel be fixed air-tight by means of a perforated cork to the neck of a bottle, and the air exhausted in the bottle, the liquid will run faster through the filter in proportion to the diminution of the pressure in the bottle. Comparative experiments, some made according to the old and others made according to the new method, showed that the filtration, washing, and drying of a precipitate, which took seven hours by the old plan, could be performed by filtration into an exhausted bottle in thirteen minutes. But a saving of time is not the only advantage of the improved method of collecting and washing precipitates. A more perfect washing with less water than is required by the common way of proceeding is by no means the least recommendation of Bunsen's ingenious method."

CHEMICAL AFFINITY.

A VERY important paper on the nature of Chemical Affinity has been submitted to the French Academy by M. Dumas, in which he maintains that the doctrines first promulgated by Newton upon this subject best accord with chemical phenomena. By affinity we understand the force which causes simple substances to unite with other simple substances to form compounds, and this force