This long talked of and much-mooted proposition seems I at length to have reached a stage of definite action. From an ; article in All the Year Hound we are enabled to gather some- thing as to the possibility of its achievement. Demonstrated j possibility, joined with desirability, seems, at the present age to be all that is necessary to initiate any engineering enterprise. The conditions on which the success of this enterprise depend are comparatively few and simple. The first condition relates to the geological formation in which the work would have to be done. It has frequently been pointed out, and there appears to be no difference of opinion on the subject, that there are to be found, on opposite sides of the Channel, tracts of coast presenting geological features almost identical. The English coast between Deal and Folkestone, for instance, corresponds in every particular with three miles of the French coast, a ! little to the westward of Calais. That the same formations continue under the bed of the sea is a probability that has j been noticed in a report to the Geological Society on " The i Chalk Ridges which extend parallel to the Cliffs on each side of the Channel tending towards the North Sea," by Captain J. B. Martin, in 1839. Careful geological investigation has ! been made with a view to discover whether the chalk forma- j tions obtaining on each coast continue unbroken for the whole j distance dividing them; and there appears no reasonable! cause of doubt that this is the case. j Impressed by these facts, Mr. William Low, an engineer I who for many years had been confident of the feasibility of I connecting the English and French railway systems, by j means of a sub-channel tunnel, set himself earnestly to examine for himself the geological formations of the two shores. After most careful examination, Mr. Low became satisfied that the deductions of the geologists were correct. His ex-1 amination of the borings for several artesian wells on both ? sides of the Channel, strengthened his opinion as to the reg- ! ularity of the strata. It became his firm conviction that along a certain line, about half a mile west of the South Foreland, and four miles west of Calais, the tunnel could be made entirely through the lower, or gray chalk, which, owing to its comparative freedom from water, and other qualities, would be a most desirable stratum in which to work. With the result of these investigations, and with plans of the ' tunnels he projected, Mr. Low, in 1867, betook himself to the Emperor ofthe French, who, giving the English projector a cordial reception, desired him further to organize his plans, and to come again when he might be prepared to submit definite proposals. In 1856, M. Thome de Gamond, a French engineer of repute, who had for many years been advocating the construction of' a tunnel between England and France, obtained, by order of j the Emperor, an investigation of his plans at the hands of a scientific commission. This body, satisfied with the substantial accuracy of M. de Gamond's geological conclusions recommended that his investigations should be practically tested by sinking pits on the two coasts, and driving a few short headings under the sea at the expense of the two governments. Owing possibly to the backwardness of the Great British Circumlocution Office, this recommendation does not j appear to have had any practical result. In 1857, M. de Gamond published the upshot of his researches, and the report of the commission : and at the Paris Exposition of 1867, he publicly exhibited his plans. It was very natural that Mr. Low, after his interview with the Emperor, should put him- j self in communication with M. Thome de Gamond. This ?! gentleman unreservedly placed his experience at Mr. Low's disposal, and, after a time, the results of their joint labors were laid before Mr. James Brunlees. He, after careful exam-1 ination, consented to co-operate with the two engineers in the prosecution of the work. A committee of French and English gentlemen of influence and position, was, by desire of the Emperor, formed to further the project; and it is by the executive committee of this body, under the chairmanship of Lord Richard Grosvenor, that the matter is now prac-. tically brought before the public. But the opinions of Messrs. Low and Brunlees, and of M. Thome de Gamond, received further confirmation. Mr. John Hawkshaw, whose name is well known to the public at large and to the engineering world, was induced to ! test the question, and to ascertain by elaborate independent investigation, the possibility of a sub-channel tunnel. With characteristic care and caution he took nothing for granted, but went himself over the whole ground already traversed by Mr. Low and by M. de Gamond. His geological researches led him to the same conclusions, and his expression of opinion in favor of the gray chalk was very decided. Not even satisfied with the theoretical results of these investigations, carefully though they were made, Mr. Hawkshaw held it j necessary to make borings on each coast, at the precise points at which the ends of the tunnel would be situated. Thus Mr. Hawkshaw and the French commission came to the same decision. Now, the well at Calais, from which a considerable part of the geological inferences had been drawn, was at some distance from the spot where it was proposed to begin the tunnel on the French side, and possibly the strata might, in the precise place indicated not run as anticipated. This did not, however, turn out to be the case. The actual borings conclusively proved the correctness of the views entertained. The boring on the English coast was commenced at St. Margaret's Bay, near the South Foreland, in the beginning of 1866, and was satisfactorily completed in 1867. It was carried completely through the chalk and into the green sand, which was reached at a depth of five bundled and forty feet below i high water. The boring on the French coast, three miles westward of Calais, was carried to a depth of five hundred and twenty feet below high water. It was intended to pass through the chalk as on the English side, but accident frustrated this design. Simultaneously with these borings the bottom of the Channel was carefully examined by means of a steamer provided with all suitable apparatus. The main useful results established by these experiments appear to be, that on the English soast the depth of chalk is four hundred and seventy feet below high water, of which two hundred and ninety-five feet ire of the gray formation, in which it is proposed to work ; that on the French coast, the depth of chalk is seven hundred and fifty feet, four hundred and eighty being gray: and that there appears to be no room to doubt the regularity af the strata between the two shores along the line proposed. So, it would seem, firstly, that the chief condition is satisfactorily insured, and the geological formation of the sea's bed is such as to admit of the excavation of a tunnel through the lower gray chalk; and secondly, that it is not necessary to go to a depth unsuitable for railway traffic. It is calculated that the approaches to the tunnel can be constructed at gradients not exceeding one foot in eighty. The next point of paramount importance to the traveling public is the question of the safety of the tunnel when made. The dangers most carefully to be guarded against are two : any possible irruption of water from the sea, or from unexpected land-springs ; and any deficiency in ventilation. Engineers are of the opinion that these dangers can all be provided against. Recent borings on either side of the Channel have proved that there need be no fear of land water, and the impermeability of chalk and the depth below the bottom afthe sea, at which the tunnel will be placed, being in no case less than one hundred feet, it is maintained that there would be no danger from incursions of the sea water. The submarine excavations in the Cornish mines are an existing lemonstration of the safety of the proposed tunnel. Ventilation will be secured by means of powerful steam engines, and attempts to raise the necessary funds are wisely ;o be postponed until two small headings, or galleries, are Iriven from each country, connected by transverse driftways. Ventilation would thus be secured in the manner customary n coal mines and works of a similar nature, and the feasibil-ty or otherwise of connecting England and France by a tunnel ;an be demonstrated. Xlie New Postofflce lor New York:. The long-talked of and prayed for new Postoffice was commenced on the 9th inst. The grounds situated at the lower 3nd of the City Hall Park, opposite the SCIENTIFIC AMERICAN office, are now inclosed by a high board fence, within which a large number of laborers are engaged in the prelim-nary work. The new building is to have frontages on Park Row, on Broadway, on the Plaza to be laid out between'it and the City Hall (or in a straight line across the Park), and on the curve at the southwesterly terminus of the Park. The style of architecture will be renaissmit. The material of the edifice is to be a light-colored granite, and, in shape, the building will be conformable to the area of the plot of ground to be built upon. It is to have three stories and an attic over the street level, and a deep basement. The roof will be of the Mansard style. The basement and first story of the building are to be devoted to postoffice purposes exclusively; the second story will contain court rooms for the United States Courts, officestfor the United States Marshal, etc., the money order and registry departments of the Postoffice and the private offices of the Postmaster; the third story will comprise principally the offices of the judges and other officers of the Federal courts, and the attic rooms will be fitted up as places of deposit for Federal records, etc. The plans for the new building will be ready for the contractors in about one month hence. The excavation for the edifice is to be thirty feet in depth, and will require the removal of more than 50,000 cubic yards of earth, as there are to be a cellar and sub-cellar. The plans are all to be drawn under the direction of Mr. A. B. Mullett, the supervising architect of the Treasury Department, who has taken rooms at the Astor House in order to be near the scene ot operations while the construction of the building is going on. An important suggestion has been made (but it is only a suggestion as yet) to connect the basement of the new Post-office with the press and mailing rooms of the prominent newspaper offices, by an underground pneumatic railway, so that there may be no delay in sending off the editions of the papers which go to the various parts of the country by mail. If the proposition be acted upon, much time will be saved to the newspaper establishments, the extra handling of the papers being avoided, and the prompt delivery of the morning journals all along the different mail routes will be assured. Mr. Mullett hopes to have the whole building ready for occupancy by September, 1871. He is assisted in his labors by Mr. Hulburd, who superintends the erection of the building; Mr. Judson York, assistant supervising architect, and, in the absence of Mr. Hulburd, acting as superintendent; and Mr. John F. Ames. With such capable and thorough assistants, it may be regarded as certain that Mr. Mullet, whose energy is well known and highly appreciated by the Government, will push, forward the work to a speedy completion, and that, when pronounced ready for occupancy, the edifice will be an ornament to the city. There are also to be important changes in the laying out of the City Hall grounds, and Broadway, from the lower corner of the Plaza to Chambers street, will be widened forty-two feet. Storms in the Sun. We now know that our own sun (resembling in this probably most other solar bodies of the same kind) is in so highly (luid and excitable a condition as to by constantly sending out from its surface forked tongues (thousands of miles in extent) of inflamed hydrogen gas, like the flickering streams of light from the stars ot a street illumination ; and, moreover, as to be subject to great periodical disturbances, now called " magnetic storms, which arc in all probability caused by certain combinations in the movements of those little solid one of which we live, round the sun. Even now one such of magnetic storm seems to be thought pretty near at hand. The sun has been lately exhibiting the most surprising forms of disturbance, and presenting to scientific eyes less " fixity" of essence than ever. Spots so vast that we must estimate their dimensions by millions of square miles, have broken out from time to time, and have presented rapid changes of figuro, indicating the action ot forces of inconceivable intensity, ('lusters of smaller spots, extending over yet vaster areas, have exhibited every form oi disturbance known to the solar physicist, and every degree of light, from the apparent blackness (in reality only relative) of the nuclei, to the intense brillancy of the faculous ridges. And we now know that these are not merely matters for the curious, with wliich, as they happen at a distance of above ninety millions of miles, practical men need not concern themselves. This much, at least, is certain, that the vast changes now going on in the physical constitution of the sun are changes which do most powerfully affect the electric condition of our earth, which have in former years caused the most violent disturbances in the various artificial as wellas natural electric appantus of the world we live in, and which, to speak of the least of all its possible effects, might, just as well as not, happen some day to throw the electric condition of every telegraphic cable on our planet, nnder the sea or above it, in the most dire confusion, and send down telegraphic companies' shares to zero in a lump, even if they did not contrive to telegraph to us, after some strange inarticulate fashion that shares in all public companies, even in that very limited public company, the human race, arc, in a physical point of view, of very doubtful valuo indeed. Let us explain briefly to what we allude. On September 1, 1350, shortly before noon, two astronomers —-Messrs. Hodgson and Carrington—one at Oxford, the other in London, were tit the same insiant scrutinizing a large group of snn spots. On a sudden two intensely bright patches of light appeared in front of the cluster. So brilliant wen; they that the observers thought the darkening screens attached to their telescopes must have become fractured. But this was found not to be the case. The bright spots indicated some process going on upon the sun's surlace—a process of such aei'vity that within five minutes the spots traveled over a space of nearly 34,000 miles. Noiv, at tiie. K''w Observatory there are self -registering magnetic, instruments which indicate the processes of change by which the subtile influences of terrestrial magnetism wax and wane. At one time the line traced by the pointer will be marked by scarcely perceptible undulations, indicating the ahnoj-it quiescent state of the great terrestrial magnet. At another, well-marked waves along the line exhibit the pulsations of th! magnetic system, influenced in a manner as1 yet intelligible io the physicist. And then there is a third form of disturbance, the sharp, sadden jerks of the pointer exhibiting the occurrence of those mysterious phenomena termed " magnetic storms." j When the records of the Kew Observatory came to be' looked over, it was found that at the very instant in which the brilliant spots of light had appeared to Messrs. Hodgson and Carrington, the w-iU-rogiatering instruments had been subjected to the third and most significant form of disturbance— a magnetic storm began, in fact, as the light broke out on the sun's surface. But this was not the only evidence of: the sympathy with which the earth responded to the solar action. It was subsequently found that soon after the spots of light hud appeared the whole frame of the earth had thrilled under a mysterious magnetic influence. At the West Indies, in South America, in Australia, wher-i vi;r magnetic observations are systematically made, the oh- j rfjvrs had the same story to tell. In the telegraph stations ! HO Washington and Philadelphia the signalmen received ptro ig electric shocks. In Norway telegraphic machinery was set on fire. The pen of Bain's telegraph was followed by a flame. And wherever telegraphic wires were in action, well-marked indications of disturbance presented themselves. KWJI iiiis, however, was not all. The great magnetic storm v-3 not. a men; instantaneous electric throe. Hours passed bo Tore the disturbed earth resumed its ordinary state. And Tsui* it happened that in nearly all parts of the earth night ! r'eii while the storm was yut in progress. During the night ? magnificent auroras spread their waving streamers over the ' sky, both in the northern and the southern hemisphere. As the disturbed needle vibrated, the colored streamers waved responsive, and it was only when the magnetic storm was subsiding that the auroral lights faded from the heavens. 1'ow, it is evident that these phenomena show the most intimate relation between these peculiar disturbances in the sun i:,al the magnetic currents of our own earth. Directly one of these changes takes place upward of ninety millions of miles iiway, tlie electric condition of our planet is changed in some mysterious way, of which our instruments, and even the con-1 vision ot our sky, bear record. The pens o1' all our telegraphic wires may some day trace in (tame a handwriting more ominous of human destiny than '? was the handwriting which during Belshazzar's feast traced a TVivruing on the wal) of the full oi the Babylonian dynasty. .Moivcvv.r, not.o Oily, thui; these- cUHtiges in the imdUkm **(' the sun take place at intervals of about eleven years. The . variable star which swings round it, as well as supplying us , with light and heat and (apparently) magnetism, clouds over . every eleven years these spots, so that it seems most likely v that every eleven years certain magnetic conditions recur - which have not occurred in the interval. If so, perhaps, the , i magnetic excitement of 1859 will recur, and it may be in much greater force next year—in 1870. And if it does, how are we to say what may or may not recur with it 1 Type Setting by Machinery. The following is a description from the Scientific Opinion ? of an invention recently patented : The type pockets are stationary, and are arranged in a circle or a portion of a cir- ? cle around or over a revolving wheel or frame, the wheel carrying a number of pickpockets, each of which is capable of withdrawing type from one of the pockets, the precise pocket upon which each pickpocket shall operate, being in one arrangement determined by the position of the perforations in a strip of paper acting in concert with a system of levers and triggers or fingers in manner as, or nearly as follows : The systems of perforations which the inventor found suitable was similar to that used in a former apparatus, in which each letter or sign is represented by two or more perforations, the distinctions between the several letters or signs being effected by changing the positions of the perforations from one to another of a series of straight lines or imaginary lines, as, for example, fourteen, which number will, in ordinary cases, be found to be sufficient. The strip of paper thus j perforated is passed by an intermittent movement over a perforated drum or plate and into contact with a series of . fourteen pins attached to, or formed on, a corresponding number of ]ever3 or triggers, each movement of the paper bringing two perforations opposite to two of the pins, which said two pins enter the said perforations,and the corresponding levers move into position to set one of the pickpockets. _--------_—..--------------. Bleaching Ivory. The following recipe for bleaching ivory is said to be very satisfactory : The ivory, when cut into plates of the proper thickness for keys, is placed in a flat vessel, and a solution of carbonate of soda, in the proportion of ten ounces of soda to two pounds of soft river water to each pound of ivory is i poured over it. This is allowed to remain for 36 or 48 hours, after which the solution is to be poured off and the ivory i washed several times in cold, soft water. After this it is to I be again immersed in a solution consisting of three quarters of a pound of sulphate of soda, and two pounds of soft water, to a pound of the ivory, and allowed to remain five or six hours. Two ounces of hydrochloric acid, previously diluted with four times its weight of water, are then to be stirred in, and the vessel covered with a tight-fitting cap, and allowed to remain 36 hours. The liquid is then poured off, and the j ivory plates well washed and dried in the air. Should the desired degree of whiteness not bo obtained by one operation, it can be repeated until successful. As the gases generated during the process are injurious to the lungs, it will be readily understood that the operation should be conducted in the open air or in a chimney, where the fumes can be carried off. Patent Bottle Stopper. A new safety stopper for bottles has been patented in England. It is composed of a short vulcanized india-rubber or cork tube, in the upper part of which is inserted a metallic ring, on which this tube is kept fast by any suitable means, either by binding, spurs, expansion, etc. A screw-tapped peg with a conical head is inserted upwards in the india-rubber tube, through which it runs, and is provided with a round screw nut at its upper part. This tube so fitted, is inserted in the neck of the bottle to be stopped, and the screw nut being turned to the right with the fingers causes this screw-tapped peg to move upwards ; the conical head of the latter entering gradually in the india-rubber tube presses it against the internal side of the neck at the very place where this neck is conical, and the bottle is hermetically closed, because the conical head of the peg presses against the india-rubber or i cork tube in its whole periphery against the conical neck of j the bottle. To open the bottle, the screw nut must be turned to the left ; then, by pushing down the peg, its conical head comes out of the rubber tube, and the stopper is easily removed. Profits of Small Inventions. Hiram Tucker lately applied for an extension of his patent for a Spring Bed Bottom. Theinvention consisted in supporting the ends of wooden slats on stirrup springs. It appeared from the patentee's sworn statement that he had cleared in 1 profits from his patent over one hundred and twenty thousand 1 dollars. Judge Fisher, the Commissioner of Patents, decided that the invention was not one of great importance to the public, that the patentee had not expended an extraordinary amount of time, ingenuity, or expense upon the invention, and that the profits already'mado were an adequate compensation. The application for extension was therefore rejected. --------------?-------- * ----------------------- FOR the sake of the future cleanliness of the city, we are glad to chronicle the fact that a new Postoffice is about to bi I erected upon the lower point of the City Hall Park. Already the filthy apple, peanut, and ice-cream stalls are cleared away, and in their stead we can look out upon a clean board ' fence. The municipal authorities of this city are constitutionally wedded t/j all sorts of nuisances, and it is vain to expect, or oven hope for anything like good order, either in *,lvt) 9tn;ts a? oihej public, phic.cH undo? sity control., PAPER FKOM SHAVINGS AND SAWDUST.—Dr. Matthiessen, a i well-known scmaiit, now appears in the character of an inventor and patentee in England of an important improvement. He submits wood when in a state of division, such as shavings, sawdust, or disintegrated wood, to what is known as a rotting process—that is to say, the wood in a state of division is steeped either in running or stagnant water, and is allowed to undergo a rotting or fermenting process, by which process certain constituents of the wood will be decomposed and removed, and the subsequent treatment of the residual ligneous fiber for the production of pulp or paper will be thereby rendered more economical, and the process of boiling and : bleaching is more easily effected. BKOADWAY has been re-paved from Bowling G reen to Union Square at a cost of very nearly $463,000. The work was commenced in the month of June, 1867, and has been going on wearily ever since, very much to the inconvenience and annoyance of those who crowd that busy thoroughfare. IN estimating the practical value of any science, something more than the mere material results of its application must be taken into account. It must be credited with whatever aid it affords to its sister sciences.