Only two of the prismatic colors were visible. The red of the pri mary was succeeded by the green; then came the faint red of the first supernumerary bow; a dark interval next occurred, which was followed by the still fainter red of the second supplementary arc.

This singular optical phenomenon usually presents a succession of green and violet; or green and red arcs, alternating with each other, like those seen by Brewster in 1828; but that supernumerary bows are sometimes formed of a single hue, is evident from what has just been stated, and from the case detailed by Prof. Twining, who beheld, at Montreal, in September, 1823, three supplementary bows of a violet or dull red tint, unaccompanied by arcs of green.

4. On some Recent and Remarkable Examples of the Protection af forded by Metallic Conductors against Heavy Strokes of Lightning; by Sir W. S. HARRIS, (Proc. Brit. Assoc., 1847, Athenæum, No. 1027, July 3.)-The possibility of guarding buildings and other structures against the destructive effects of lightning, has been made a great question in practical science, from the time of Franklin to the present day; and it is of considerable public importance, seeing the frequent damage which occurs to our beautiful churches and other edifices by strokes of lightning, to bring this question completely under the dominion of induction, observation and experiment. The general principles which Sir W. S. Harris submitted as deducible from the inquiries to which he alluded are these:-If we imagine a ship or building to consist altogether of metallic substances, it would certainly be secure from any damage by lightning and for this simple reason, that what we call lightning is the result of the electrical agency forcing a path through resisting matter such as the air, and extricating, with explosive and expansive force, both light and heat in its course. When, on the contrary, it falls upon comparatively non-resisting bodies, such as the metals, then this form of lightning vanishes, and the discharge assumes, if the metallic body be sufficiently capacious, the form of a comparatively quiescent current. Our object should be, therefore, in defending any building or ship from lightning, to bring the general mass so far as possible into that passive or comparatively non-resisting state it would have supposing it a mass of metal. This is, in fact, the single and simple condition of such an application, without any reference whatever to assumed forces of attraction or peculiar specific powers manifested by certain bodies for the matter of lightning, and which really do not exist. This simple principle, by a careful mechanical arrangement calculated to render it practical and applicable to all the duties which the general structure of a ship together with its masts has to perform, is now universally carried out in the navy, with the most perfect success; so that damage by lightning in the vessels so fitted has, for the last fifteen years, quite ceased. The masts are made completely conducting by capacious plates of copper, reaching from the highest points to the keel; and are tied into one general connexion with all the great metallic masses employed in the construction of the hull, and united by large bolts of copper passing through the keel and sides, with the copper expanded over the bottom and with the sea. It is quite impossible that a discharge of lightning can fall on the vessel in any place, and not be at once transmitted safely by the conductors

without, not under the form of lightning, but under the form of a current explosion. Sir W. S. Harris then referred to some remarkable cases.

5. On the Colored Glass employed in Glazing the new Palm House in the Royal Botanic Garden at Kew; by R. HUNT, (Proc. Brit. Assoc., 1847, Athen., No. 1028.)-It has been found that plants growing in stove houses often suffer from the scorching influence of the solar rays, and great expense is frequently incurred in fixing blinds to cut off this destructive calorific influence. From the enormous size of the new Palm House at Kew, it would be almost impracticable to adopt any system of shades which should be effective-this building being 363 feet in length, 100 feet wide and 63 feet high. It was therefore thought desirable to ascertain if it would be possible to cut off these scorching rays by the use of a tinted glass, which should not be objectionable in its appearance, and the question was at the recommendation Sir Wm. Hooker and Dr. Lindley, submitted by the Commissioners of Woods, &c. to Mr. Hunt. The object was, to select a glass which should not permit those heat rays which are the most active in scorching the leaves of plants to permeate it. By a series of experiments made with the colored juices of the palms themselves, it was ascertained that the rays which destroyed their color, belonged to a class situated at the end of the prismatic spectrum which exhibited the utmost calorific power, and just beyond the limits of the visible red ray. A great number of specimens of glass variously manufactured were submitted to examination, and it was at length ascertained that glass tinted green appeared likely to effect the object desired most readily. Some of the green glasses which were examined obstructed nearly all the heat rays-but this was not desired-and from their dark color these were objectionable, as stopping the passage of a considerable quantity of light, which was essential to the healthful growth of the plants. Many specimens were manufactured purposely for the experiments by Messrs. Chance of Birmingham, according to given directions, and it is mainly due to the interest taken by these gentlemen that the desideratum has been arrived at. Every sample of glass was submitted to three distinct sets of experiments-1st. To ascertain, by measuring off the colored rays of the spectrum, its transparency to luminous influence. 2nd. To ascertain the amount of obstruction offered to the passage of the chemical rays. 3rd. To measure the amount of heat radiation which permeated each specimen. The chemical changes were tried upon chlorid of silver, and on papers stained with the green coloring matter of the leaves of the palms themselves. The calorific influence was ascertained by a method employed by Sir John Herschel, in his experiments on solar radiation. Tissue paper stretched on a frame was smoked on one side by holding it over a smoky flame, and then while the spectrum was thrown upon it, the other surface was washed with strong sulphuric ether. By the evaporation of the ether, the points of calorific action were most easily obtained, as these dried off in well defined circles long before the other parts presented any appearance of dryness. By these means it was not difficult, with care, to ascertain exactly the conditions of the glass, as to its transparency to light, heat, and chemical agency, (actinism.) The glass thus chosen is of a very pale yellow-green color, the color being given by oxyd of copper, and is so transparent that

scarcely any light is intercepted. In examining the spectral rays through it, it is found that the yellow is slightly diminished in intensity, and that the extent of the red ray is affected in a small degree, the lower edge of the ordinary red ray being cut off by it. It does not appear to act in any way upon the chemical principle, as spectral impressions obtained upon chlorid of silver are the same in extent and character as those procured by the action of the rays which have passed ordinary white glass. This glass has, however, a very remarkable action upon the non-luminous heat-rays, the least refrangible calorific rays. It prevents the permeation of all that class of heat-rays which exists below and in the point fixed by Sir William Herschel, Sir H. Englefield, and Sir J. Herschel, as the point of maximum calorific action. As it is to this class of rays that the scorching influence is due, there is every reason to conclude that the use of this glass will be effective in protecting the plants, and, at the same time, as it is unobjectionable in point of color, and transparent to that principle which is necessary for the development of those parts of the plant which depend upon external chemical excitation, it is only partially so to the heat-rays, and it is opaque to those only which are the most injurious. The absence of the oxyd of manganese, commonly employed in all sheet glass, is insisted on, it having been found that glass, into the composition of which manganese enters, will, after exposure for some time to intense sunlight, assume a pinky hue, and any tint of this character would completely destroy the peculiar properties for which this glass is chosen. Melloni, in his investigations on radiant heat, discovered that a peculiar green glass, manufactured in Italy, obstructed nearly all the calorific rays; we may, therefore, conclude that the glass chosen is of a similar character to that employed by the Italian philosopher. The tint of color is not very different from that of the old crown glass; and many practical men state that they find their plants flourish much better under this kind of glass than under the white sheet glass, which is now so commonly employed.

6. On the Application of Gutta Percha for Modeling; by Mr. BUSK, (Proc. Brit. Assoc., Athen., No. 1027.)-After alluding to his experiments, he described the mode he followed in obtaining his moulds :-"It is to be rolled out on a smooth surface in sheets of any convenient size suitable to the object to be taken, and varying in thickness according to the size. For small objects, from the to of an inch is thick enough. The sheet is dipped for a moment or two into boiling water, and placed warm upon the object, upon the surface of which it is to be carefully pressed with the finger point, or a convenient elastic pad, so as to insure its close and uniform adaptation. In moulding soft objects it is, of course, necessary that they should possess elasticity or resiliency, as is the case with living or recently dead animal bodies. The gutta percha does not seem to be applicable to taking moulds from very fragile bodies,-such as many fossils, which would not bear the requisite pressure nor admit of the removal of the mould when rigid without risk. The most delicate objects, however, and slender projections, if firm enough in the original, may in the plaster cast be removed from the matrix without any difficulty when the latter is softened by momentary immersion in hot water.

Mr. Jerdan stated that there were two kinds of gutta percha-one white, the other black. The former was the best for modelling. He had written to Mr. Brooke, of Borneo, on the subject, who informed him that an unlimited supply might be obtained from that country.-Mr. Crawfurd said it was not hard till after it was submitted to the heat of boiling water. The proper way of pronouncing the word was gutta pertsha, which was a Malay term, and signified ragged gum.

7. Report on Atmospheric Waves; by W. R. BIRT, (Proc. Brit. Assoc. for 1847, Athen., No. 1028.)-The author in introducing his fourth Report on this subject observed, that in accordance with the resolution adopted at the last Meeting of the Association, about thirty sets. of observations had been obtained from various stations in the British islands; the extremes of the area embraced being the Orkneys and Jersey in one direction, and Galway and Dover in the other. As instances of the increasing interest manifested on this subject, he remarked that he had been furnished with curves from stations in the north, where the barometric movements had been considered to result from the transit of the great November wave. Each of these curves was referred to the same period; namely, from the 2nd to the 17th of November; and the observers invariably regarded the regular rise and fall that occurred between these epochs as indicating a well-marked return of the great symmetrical wave. Mr. Birt, after noticing the remarkable circumstances under which the wave returned last autumnso remarkable that they had no small tendency to mask the waves in the southeastern part of the island-stated that the projected curve at London strikingly developed its essential features; the five subordinate waves were well seen, although the inflexions were not strong, owing to the small altitude of the wave on its last return, scarcely exceeding half an inch-its whole development occurring above thirty inches prevented the boldness of the inflexions particularly noticed on the occasion of its return in 1842. The author then proceeded to notice the essential features of the curves as obtained from observations at Ramsgate, St. Vigean's, near Arbroath, east coast of Scotland, the Orkneys and Western Isles, Applegarth Manse, Dumfries-shire, Largs, Limerick, Galway, Helstone in Cornwall, and St. Helier's Jersey.

We

Our limits will not permit us to give in detail the resemblances and differences of these curves, exhibiting, as they do, the distribution of pressure around Great Britain and Ireland, which the author traced from the southeastern point towards the northwest: but the report will be printed in the forthcoming volume of the transactions. may, however, here notice that attention was called to the principle which the author laid down in his report of last year, "that the barometric curve, including a complete rise and fall at any one station, does not represent any reality in nature, but is the effect of two or more systems of waves or currents moving in different directions and crossing each other at various angles." He also pointed out the great extent of oscillation (nearly double) observed in the northwest as compared with the southeasterly observations. The great wave commenced on the 2nd of November; at the northern stations it culminated on the 12th; at the southeastern on the 9th; and it terminated on the 17th. In explaining the differences of epoch as indicating the transit of the crest SECOND SERIES, Vol. IV, No. 12.-Nov., 1847.

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being much earlier in the southeast than in the north, Mr. Birt remark. ed that the observations clearly showed that the barometer passed two maxima, one on the 9th, the other on the 12th; and that the whole extent of the British isles might be divided into two barometric areas, distinguished in one case by the superiority of the maximum of the 9th, and in the other by the superiority of the maximum of the 12th. A line passing between Arbroath and Newcastle, south of Dumfries, and between Ireland and Wales, separates these areas. Northwest of this line we find the maximum of the 12th superior; southeast of it we find the maximum of the 9th superior. The maximum of the 9th Mr. Birt regarded as the central wave forming the crest of the great wave, and the maximum of the 12th he considered as the crest of the first subordinate wave on the posterior slope.

The author next proceeded to examine the distribution of pressure as manifested by these observations; from which, in connexion with the features of the projected curve, he deduced the following results:-1st. The return of the great symmetrical wave. This occurred in the southeastern angle of our island under very peculiar and remarkable circumstances. The area of greatest symmetry is closely in accordance with the results of former discussions, and goes far to confirm the result deduced from the examination of Sir John Herschel's hourly observations, "that Brussels is entitled to be considered as a point of comparatively gentle barometric disturbance, * and may be regarded as in a certain sense a nodal point, where irregularities are smoothed down and oscillatory movement in general is more or less checked, and such movements increase as we recede from Brussels as a centre, especially towards the northwest." The curve of greatest symmetry was obtained from Ramsgate, the nearest station to Brussels. As we proceed towards the northwest, the symmetry is considerably departed from, especially by the greater development of the first subordinate wave on the posterior slope, by which the maximum of the 12th became superior. This portion of the wave formed a striking contrast to the similar portion in 1845, which was characterized by a considerable depression.

It is not a little curious, remarked the author, and goes far to show that we are approaching the true explanation of the nodal character of Brussels, to observe that movements so dissimilar in their character, so opposite in their value, and presenting themselves under such a diversity of aspects, should, in a certain locality and on particular lines of country, manifest, by means of the barometer, constant and well defined phenomena, that may be recognized year after year, and which give to the curves of barometric rise and fall during the period of their occurrence a peculiar symmetrical appearance. 2nd. Two systems of waves or currents, one having a general direction of progress from the northwest, the other from the southwest, traversed the area during the period of the great wave. This is the same result to which we were conducted by an investigation of the symmetrical wave of 1842. The relative positions of the individual waves were somewhat different from those of the wide bi-dual waves of 1842; but there were some striking points of resemblance. The northwesterly system in each case exhibited the largest wave, both as regards amplitude and altitude. The intervals between similar phases of northwesterly waves were nearly