ANY TWO PLACES ON THE SURFACE OF THE EARTH, ETC. phical mile is to the English mile, as 1.15 to 1 very nearly; hence we have 3033.5 × 1·15=3488.5 English miles, for the direct distance between Liverpool and Halifax. Note. The above process is not precisely that which is indicated by the formula; but it is tantamount to it, and saves the trouble of a subtraction in taking the complements of the latitudes, for it is obvious, that the sine of the complement is the same as the cosine, and the cosine of the complement the same as the sine. Longitude of Cape Churchill...... 93° 12' 0" West. Sum of the longitudes.............. 95 32 30 East. ... ... ... 0.32927 sub. +0.64395 Nat. cos. b=+0.31468 7 EXAMPLE 2.-What is the direct distance between the Observatory of Paris, in latitude 48° 50′ 12′′ North, and longitude 2° 20′ 30′′ East, and Cape Churchill, in latitude 58° 48' North, and longitude 93° 12′ West ? Here the latitudes are both north, and the longitudes one east and the other west; consequently, the sum is the angle contained between the meridians of the places; and being greater than a right angle, it agrees with the second case. Hence it is log. cos. 8.984840 log. cos. 9.714352 ... log. sin. 9'932151 log. 9.517555 log. 9.808851 nat. num. 40.64395 22° 54′ 42′′ South, and longitude 43° 9' West? Here the latitudes are the one North and the other South, and the longitudes both West; and since their difference is less than 90°, the example falls under the third case. Hence it is, Difference of the longitudes......... 40 9 30 log. cos. 9.883244 ... log. cos. 9.775308 +0.41962 Nat. cos. b 0.10703; therefore, we have b=83°51′20′′-5031.3 geographical miles, or 5786 English miles, the distance sought. log. 9.622862 the latitude is 12° 33′ North, and longitude 53° 23′ East? In this example both the latitudes and longitudes are of different names, and the sum of the longitudes is greater than 90°; the example therefore falls under the fourth case, and is thus resolved : EXAMPLE 4.-What is the direct distance between Fort Villagagnan, in Brazil, the latitude and longitude being as in the last example, and the western extremity of the island of Socotra, of which Longitude of Fort Villagagnan 43° 9' 0" West. Longitude of W. extr. of Socotra.. 53 23 0 East. Sum of the longitudes 0 log. cos. 9.056071 Latitude of Fort Villagagnan ...... 22 54 42... log. cos. 9.964310 Latitude of W. extr. of Socotra 12 33 0 ... log. cos. 9.989497 b=180°—79° 13′ 20′′-100° 46′ 40′′-6046-66 geographical miles, " 8 BAILLIE'S PATENT TRANSPARENT SLIDE-VALVE VENTILATOR. or 69533 English miles, the distance sought. Since these four examples illustrate all the cases of which the problem is susceptible, it is only necessary that the reader should pay particular attention to the signs of the quantities as they arise in these cases, to avoid any error that may result from the different relations of the angular magnitudes. rack-pulley, n, in the same way as in ordinary roller-blinds; but when it is a 7/2 BAILLIE'S PATENT TRANSPARENT SLIDE- In the ordinary glass louvre ventilators each of the louvres turns on a separate axis, and as long as the whole keep in equally perfect working order, the whole may be opened to any uniform extent, or altogether closed. It rarely happens, however, that the whole remain. for any length of time in the same trim; some will not turn as freely, or to the same extent, as others; while one or two will not move at all, either one way or another; the ventilation becomes, in consequence, proportionally inefficient ; the streams of air enter at different, often very conflicting angles; and permanent draughts are established where occasional currents only were wanted. In the present ventilator we have all the advantages of the glass louvres, free from any of these objections. It consists, firstly, of a series of louvres, which are permanently fixed at a certain inclination, so that the currents of air may be deflected upwards in one uniform direction; and secondly, of a sliding valve, likewise of glass, by which the quantity of air admitted may be regulated at pleasure, and which, when closed, renders the openings perfectly air-tight. The whole is contained in a neat frame, which may be readily adapted by a common glazier to any of the panes of a window. Fig. A is an elevation and a vertical section of a sash-window, with a ventilator of this description, fixed in the position which experience has proved to be the best for avoiding draughts. a a are the fixed glass louvres; b c, the slide valve for regulating the quantity of air admitted, which is moved by the cords de, coinciding with, and hidden by, the sash-bars, and passing over pulleys (as at fg hj) to any required position. The cord is represented in the figure as being finally passed over a THE BRITISH ASSOCIATION-CAMBRIDGE MEETING, 1845. indicated arise from having the louvres stationary, instead of being moveable. For example:-First, the draught of cold air is avoided, which, in the case of moveable louvres, enters through the intervals that are required to be left between their ends and the sides of the frame. Secondly, the apparatus has no joints, nor other working parts, where the dust can accumulate and become hardened, so as to obstruct their action. It may be closed in a perfectly air-tight manner, even in the most dusty situations. Thirdly, its construction is so simple, that nothing but rough usage can injure it; and if out of order, it may be repaired by any ordinary workman. And fourthly, the cord or line by which the sliding valve is opened and shut (when such is used) may be carried to any part of a room, such as the bed-side, in the same manner as a bell-rope. We have had one of these ventilators fixed for some time in our own office, and should be wanting in thankfulness for the comfort it has afforded us, were we not to recommend it warmly to friends. BRITISH ASSOCIATION-CAMBRIDGE our Sir John Herschel, President. [Selections from the Reports of the proceedings in the Athenæum and other journals.] Barometrical Pressure.-New Discovery Expedition. The Antarctic Voyage of Sir James Ross has conferred a most important accession to our knowledge in the striking discovery of a permanently low barometric pressure in high south latitudes over the whole Antarctic ocean-a pressure actually inferior by considerably more than an inch of mercury to what is found between the tropics. A fact so novel and remarkable will of course give rise to a variety of speculations as to its cause; and I anticipate that it will furnish one of the most interesting discussions which have ever taken place in our Physical Section. The voyage now happily commenced under the most favourable auspices for the further prosecution of our Arctic discoveries under Sir John Franklin, will bring to the test of direct experiment a mode of accounting for this extraordinary phenomenon thrown out by Colonel Sabine, which, if realized, will necessitate a complete revision of our whole system of barometric observation in high 9 latitudes, and a total reconstruction of all our knowledge of the laws of pressure in regions where excessive cold prevails. This, with the magnetic survey of the Arctic seas, and the not improbable solution of the great geographical problem which forms the chief object of the expedition, will furnish a sufficient answer to those, if any there be, who regard such voyages as useless. Let us hope and pray that it may please Providence to shield him and his brave companions from the many dangers of their enterprise, and restore them in health and honour to their country.-The President's Address. Repeal of the Glass Duty. A very great obstacle to the improvement of telescopes in this country has been happily removed within the past year by the repeal of the duty on glass. Hitherto, owing to the enormous expense of experiments to private individuals not manufacturers-and to the heavy excise duties imposed on the manufacture, which has operated to repress all attempts on the part of practical men to produce glass adapted to the construction of large achromatics, our opticians have been compelled to resort abroad for their materials-purchasing them at enormous prices, and never being able to procure the largest sizes. The skill, enterprise, and capital of the British manufacturer have now free scope, and it is our own fault if we do not speedily rival, and perhaps outdo, the far-famed works of Munich and Paris. Indeed, it is hardly possible to overestimate the effect of this fiscal change on a variety of other sciences to which the costliness of glass apparatus has been hitherto an exceeding drawback, not only from the actual expense of apparatus already in common use, but as repressing the invention and construction of new applications of this useful material.-The President's Address. Dr. SCORESBY described a large magnetic machine which he had constructed, with some results of its action. The principal part of the machine consists of two cases, or fasciculæ of magnetic bars, of unusually large dimensions, on principles which may be thus summarily stated: 1. That magnetic bars designed for large combinations may be conveniently constructed of various pieces; that the separation of a long bar, say of three or four, into several portions, is not disadvantageous in regard to power, and that the resulting power is similar, whether in the combining of several series of short bars the elementary bars be of the same or of unequal lengths. 2. That the relative powers of magnets, whether single or com 10 BRITISH ASSOCIATION-CAMBRIDGE MEETING, 1845. pound, when different in mass, but proportional in all their dimensions, are not in the ratio of the masses, the large masses being less strong proportionally than the smaller. 3. That whilst magnets of large dimensions are less powerful with respect to their masses than small magnets to which they are exactly proportional in all their dimensions; and whilst the increase of the dimensions continually deteriorates from the energy due to the mass: yet magnets may be combined in such proportional dimensions with a constant increase of power ad infinitum. From this last result it follows, that magnets indefinitely small must be indefinitely strong; and may indicate that the mutually attractive forces of the ultimate magnetic elements may be as strong as that by which the metallic elements are themselves combined. It must also be kept in mind that the steel should be perfectly hard; and the elementary plates of the magnet should be made of steel, converted out of one or other of the very best qualities of common iron. All the conditions, with the exceptions of thinness, were attended to in the large magnet constructed by Dr. Scoresby. A magnet on this principle, of the size of the lower mast of a first-rate ship of war, would produce a deviation of nearly l' at the distance of a mile, and a sensible effect much beyond that. The electrical effects of Dr. Scoresby's magnet, with a very imperfect armature, were, it decomposed water, rapidly producing about one cubic inch of the gases a minute; with about sixty-five yards of coiled wire, the effervescence seemed as violent as during the action of dilute sulphuric acid or zink. Copper was deposited from a solution of sulphate of copper at the rate of about 1.2 grain per minute. Shocks and scintillations were thrown out; and sparks were visible in daylight, and emitted audible sounds when the armature revolved so slowly as once in sixteen seconds. Prof. FORBES had little doubt that Dr. Scoresby could construct very powerful magnets; but he thought that as electromagnets, so much more powerful, were so readily made, it was almost useless to incur the expense of the others. April is much the driest month; and there is nearly as much rain in it from the northern portion of the compass as from the southern. With regard to the gross amount which fell from each point in the entire year, that which fell from S., S.W., and W., is much above the average; from the other points it is below it. If the polygon which characterizes the yearly rain be divided by a line running N.E. and S.W., then the rain at equal intervals on either side of this line is equal, to all but a fraction of an inch. This is the more remarkable, as these two points had been fixed on by Professor Dove as being the points of greatest and least barometric pressure; that is to say, the wind being supposed at S.W., any shift of it either towards S. or W. produces a rise of the barometer, and also any shift on either side of N.E. a corresponding fall. Now, in the case of the rain, the greatest amount is from S.W., corresponding with the least height of the barometer; the least is from N.E., where also the barometer is highest; and on either side of this line it varies regularly. For instance, the amounts from W. and S. are nearly equal, and both less than that from S.W. N.W. and S.E. are also equal, but still less; and so on. There is one particular in which this separation of the gross amount of rain into the eight portions, as brought by different winds, may be useful; viz., in ascertaining the respective specific gravities, and the amount of saline matter brought from each direction. This may be useful in regard to agricultural matters. For instance, we could easily suppose a case of two portions of land, not many miles asunder, but on different sides of a high range of hills, getting different amounts of salt, from one being exposed to, and the other sheltered from that wind in which the greatest amount was found. But by this mode of collecting the rain, an accurate mode of estimating this is within our reach. To the question, namely, the amount of solid and gaseous matter brought in the rain from each direction, Mr. Knox hopes on a future occasion to turn his attention. The tables which accompany this communication give the amount of the rain corresponding to each wind, for each separate month in the five years. The following are the yearly mean results, deduced from the whole series. S. S.W. W. N.W. N. N.E. E. S.E. 6.548 10.639 6.034 2.789 2.352 2.172 2.251 3.173 Total. 35.958 Mr. DovE said, that according to the hypothesis, that the meteorological phenomena of our latitudes may be explained by two currents, a polar and an equatorial, VOLTAIC REDUCTION OF ALLOYS. which mutually replace each other, a distinction is to be drawn between two kinds of rain, the one caused by refrigeration of the southern current coming into higher latitudes, the other when the southern current in the place of observation is overpowered and replaced by the northern. The first takes place when the vane is S. W., the latter when the vane passes from S.W. through W. to N., or from E. through S. to S.W. The direction N.E. indicates the polar stream without condensation. Hence it follows, that the quantity of rain is a maximum at S.W., a minimum at N.E., and is distributed symmetrically on either side. The Bishop of NORWICH expressed the satisfaction which he felt at hearing the communication of Dr. Lloyd, and his hopes that extended series of similar observations would soon be put on record. The great and anomalous varieties in the quantity of rain which fell in various localities would, he had no doubt, be found such as to create surprise. Thus, in London the quantity was only 23 inches annually, while in the neighbourhood of his residence it was no less than 33.-Sir JOHN HERSCHEL said that the importance of such observations, when well conducted, could scarcely be over estimated; he believed the discrepancy in the amount of rain which fell in several parts of England was still greater than had been stated by the Bishop of Norwich. If his memory did not deceive him-while in London the annual depth was only 23 inches, in Keswick it was no less than 60.-Mr. ROBERTS observed, that the discrepancies in the registries of rain-gauges were such as to render great caution necessary in drawing conclusions. It was now beginning to be understood that unless the rain-gauges were placed on a level with the earth, no indication would be obtained from them of the quantity which fell on the surface.-The Astronomer Royal said that there was something still unexplained as to the effect of the altitude at which the rain-gauge was placed, on the amount of rain received; while the quantity of rain received in the gauge on the top of the Observatory was less than that placed in the court below, yet a gauge placed at the foot of Greenwich Hill, which was at a considerably lower level than either, received less rain.-Sir J. HERSCHEL believed that the cold drop as it descended from above received accessions from the vapour of the air through which it passed; and if this be the true account, then the explanation was complicated by the relative hygrometric states and temperatures of the several strata of air. Furnace Gases. 11 Voltaic Reduction of Alloys. A paper on this subject, by Mr. C. V. WALKER, was read. It had for its object to explain the methods by which the author has succeeded in throwing down metallic alloys from compound solutions by the action of galvanic electricity. The process adopted is to prepare a strong solution of cyanide of potassium, and commence electrolyzing it, by means of a copper anode; as soon as copper begins to be dissolved, the copper anode is removed, and its place supplied with one of zink; after the action has continued for some little time, brass will be liberated on the cathode. The solution is now ready for use, and is operated upon by two or three Daniell's cells, and with a brass anode. By similar means alloys of gold and copper, or gold and silver, may be deposited. The author reasons, that true brass is a definite chemical compound; and observes, "It appears possible that the anode, which is a brass of commerce, is a true alloy, plus an excess of zink; that the solution it produces is a |