be heated by the precipitation of one gramme of the metal from a solution of any of its salts; and that those in the second column express the degrees through which the same weight of water would be raised by the precipitation of an equivalent (oxygen 1) of the same metal. If three metals, A, B, C, be so related that A is capable of displacing B and C from their combinations, and also B capable of displacing C; then the heat developed in the substitution of A for C will be equal to that developed in the substitution of A for B, added to that developed in the substitution of B for C; and a similar rule may be applied to any number of metals similarly related. Several illustrations of this principle are afforded by the preceding table. Thus The experimental result for the last case is 3435°, which in such inquiries may be considered to be identical with the theoretical number. Again, The experimental result is 5747°, which differs 3rd part from theory. This difference only corresponds to an error of about 0°04 among the three experiments, and the agreement may therefore be considered satisfactory. By applying the same principle, we can easily deduce the amount of heat developed in other cases of metallic substitution. Thus an equivalent of mercury displaced by zinc should give 731 units of heat, of platinum displaced by copper 7650 units, by mercury 6919 units, &c. upon the great VI. Report of Observations made upon the Tides in the Irish Sea, and Received March 22,-Read March 29, 1848. SIR, London, February 19th, 1848. It is with much pleasure I lay before you the result of observations which have been made upon the tides in the Irish Sea, during the execution of the survey which has been entrusted to my charge. in the Irish Up to the period of these observations the set of the tides in the Irish Sea had The stream been greatly misunderstood, owing to the association of the turn of the stream with Channel the rise and fall of the water on the shore; and it was generally understood that as hitherto misHolyhead was three hours later in its tides than places at the entrance of the channel, a vessel starting with the first of the flood would carry nine hours' tide in her favour in her run up channel and vice versa. This was an error sufficiently great in itself, but it was liable to be increased by an entire ignorance as to the time when a vessel would take any particular tide; for the times of high water by the shore were very various on different sides of the channel. understood. stream north and The present inquiry, I am happy to inform you, has set these errors and doubts at rest. The observations have shown that, notwithstanding the variety of times of high water throughout the channel, the turn of the stream is simultaneous; that the Turn of the northern and southern streams in both channels commence and end in all parts simultaneous (practically speaking) at the same time, and that time happens to correspond with throughout the time of high and low water on the shore at Morecombe Bay; an estuary rendered south remarkable as being the point where the opposite tides coming round the extremities channels. of Ireland, finally meet. So that it is necessary only to know the times of high and Meeting of low water at Morecombe Bay to determine the hour when the stream of either tide will commence or terminate; a fact which will, I am sure, be fully appreciated by every person navigating the Irish Channel at night, or in thick weather. The chart of curves or lines of direction of the stream, Plate II., which accompanies this report, will show at once the effect of the tide upon a vessel wherever she may be placed in the channel, and especially direct her where, with a beating wind, tides. Peculiar tides. she will be benefited by standing in shore or otherwise; and will warn her of the danger of drawing near the shores of Cardigan or Caernarvon Bays, with particular tides and scant winds, and so likewise of the danger of standing close to the banks skirting the Irish coast in light winds. But it is not to the navigator alone that these observations will, I hope, be found useful: they will, I think, be interesting to men of science. Taken in connection with the very valuable series of observations which were carried round Ireland by the Ordnance at the suggestion of Professor AIRY, we are made acquainted with several curious facts: first, that whilst it is high water at one end of the channel, it feature of the is low water at the other; that the same stream makes both high and low water at the same time; that there are two spots in the channel, in one of which the stream runs with considerable velocity without the water either rising or falling, and in the other, that the water rises and falls from sixteen to twenty feet without having any visible horizontal motion of its surface; and that during the first half of the flowing, and last half of the ebbing, tide-wave, the stream in the south channel runs in a contrary direction to the wave, and goes up an ascent of about one foot in 4 miles. (See Plate IV.) To the lines of direction of the stream I have added the rate of the tide at its greatest velocity on the day of syzygy, and have reduced all to the same standard. I shall now proceed to describe the general course of the streams throughout the channel; point out the situations in which the meeting of the tides occurs; and offer such remarks on the course of the stream and upon the tidal phenomena of this sea, as will, I conceive, benefit the navigator, and be interesting to science. An inspection of the chart (Plate II.) will show that the tide enters the Irish Sea by two channels; of which Carnsore Point and Pembroke are the limits of the southern one, and Rathlin and the Mull of Kintire the boundaries of the northern. The stream in the southern channel (as before stated) has been ascertained to move simultaneously in one vast current throughout; running six hours nearly each way, at an average rate of from two to three knots per hour at the height of the springs, increasing to four knots and upwards near the banks and at the pitch of Times of the headlands; its times of slack water corresponding sufficiently near for all pracslack water tical throughout with the times of high and low water for the day at Morecombe Bay, or purposes, the channel. more correctly at Fleetwood, which is twelve minutes earlier than Liverpool. Course of the tion of the south The central portion of the stream of flood or ingoing stream, runs nearly in a line central por- from a point midway between the Tuskar and the Bishops, to one six miles due west stream in the of Holyhead; beyond which it begins to expand eastward and westward, but its main body preserves its direction straight forward for the Calf of Man, which it passes to the eastward with increased velocity as far as Langness Point, and then at a more moderate rate on towards Maughold Head. Here it is arrested by the flood or southern stream from the north channel coming round the Point of Ayre, and channel. |