W. WORBY BEAUMONT, Mem.Inst.C.E., "Mechanical Road Carriages." Four Lec tures. April 27, May 4, 11, 18. MEETING FOR THE ENSUING WEEK. MONDAY, JAN. 5. Chemical Industry (London Section), Burlington-house, W., 8 p.m. 1. Dr. J. T. Hewett, "Note on the Fluorescence of Naphthalic Anhydride." 2. Dr. J. Lewkowitsch, "The Saponification of Fats and Oils by Means of Dilute Acids." Camera Club, Charing-cross-road, W.C., 8 p.m. Mr. J. W. Woodall, “Nautical Astronomy, from a Yachtsman's Point of View." Victoria Institute, 8, Adelphi-terrace, W.C., 4} p.m. The Rev. Professor D. S. Margoliouth, Forecast of the Future of Islam." London Institution, Finsbury-circus, E.C., 4 pm. TUESDAY, JAN. 6...Royal Institution, Albemarle-street, W., THURSDAY, JAN. 8...Antiquaries, Burlington-house, W., 8 p.m. Civil and Mechanical Engineers, Caxton-hall, West- Royal Institution, Albemarle-street, W., 8 p.m. Mathematical, 22, Albemarle-street, W., 8 p.m. FRIDAY, JAN. 9..United Service Institution, Whitehall, Geographical Association, College of Preceptors, to render an animal conspicuous to its enemy, easily recognised, and easily remembered. Journal of the Society of Arts, They are invariably associated with some an exceptional mode of defence, such as unpleasant taste or smell, irritating hairs, stings, the poison fang, &c. When an enemy has once experienced any of the unpleasant methods of protection it signally desires to avoid such prey in the future, and then the conspicuous warning appearance has the advantage that it is readily learnt and remembered. And it is a great advantage to animals with a warning appearance, that their enemies should learn their lesson easily, for this means a small waste of life instead of a large waste. It must not be supposed, however, that warning colours appeal to all enemies in the same way, for even the most distasteful animal will have certain foes which destroy it, in spite of the distastefulness. Good examples of warning colours are seen in the conspicuous black-and-white American skunk (Mephitis) defended by the power of omitting an intolerable odour, in the yellow and black salamander, and in many conspicuous caterpillars, moths, and butterflies. In poisonous snakes it is common for the approaching enemy to be warned off by an intimidating attitude, as in the cobras, or by sound as in the Animals rattle-snake or in the Indian Echis. which can bite, such as lizards, or strike hard, such as large birds, are also apt to resort to intimidating attitudes. Even large caterpillars may assume a cobra-like appearance, but this is, as a rule, pure imposture (protective mimicry). Another interesting point about warning colours is the tendency for the same colours and patterns to be used over and over again in the same country, so that enemies have not to learn as many appearances as there are specially defended animals. This results in the further saving of life during education, as was first pointed out by the great German naturalist Fritz Müller. Thus, distasteful butterflies often gain the same colours and patterns, and so do the stinging insects, strongly-smelling bugs, and the most highly protected beetles. A very remarkable side of the subject has only recently been investigated. Certain African butterflies which are beautifully concealed from their enemies, and live in the winter season (e.g., Precis sesamus), are proved to be the same species as certain others which are extremely conspicuous, and fly during the moist summer (Precis octavius). In fact, one species of butterfly, having many generations in the year, produces conspicuous generations in the summer, and concealed generations in the winter. The one has been bred from the other in Rhodesia by Mr. Guy Marshall. This extraordinary alternation can be explained by supposing that the butterfly is insect-eating moderately unpalatable to animals, so that it is to the advantage of the generations which exist in a time of plenty to warn their enemies, but to those flying in a time of comparative scarcity to hide from their enemies. Another kind of marking is beneficial in directing the attention of an enemy away from a vital part, such as the head or body. Thus the tails of lizards easily come off, and then become themselves most active, jumping about with the greatest vigour. They probably distract the attention of an enemy from an escaping lizard. Similarly, light patches of colour, eye-spots, and tail-like projections on the wings of butterflies divert the attention of enemies from the vital structures. Certain species of hermit crabs attach to their shells in which they live, other animals with special defences and bright warning colours, such as stinging sea-anemones, or unpalatable sponges. This corresponds to the use of foreign bodies for the purpose of concealment, as illustrated in the first lecture. Recognition markings for, as it were, signalling to friends or other individuals of the same species are probably much less common than warning colours. They are most fully developed in animals which go about in numbers and whose safety depends upon keeping together or on the younger and less experienced following the older to a place of safety. The CHAIRMAN (Mr. R. Brudenell Carter, F.R.C.S.) proposed a vote of thanks to Prof. Poulton, for his interesting course of lectures, which was carried unanimously. LIST OF MEMBERS. The new edition of the List of Members of the Society is now ready, and can be obtained by members on application to the Secretary. COVERS FOR JOURNAL. For the convenience of members wishing to bind their volumes of the Journal, cloth covers will be supplied, post free, for 1s. 6d. each, on application to the Secretary. Proceedings of the Society. CANTOR LECTURES. "THE FUTURE OF COAL GAS AND ALLIED ILLUMINANTS." BY PROFESSOR VIVIAN B. Lewes, Royal Naval College, Greenwich. Lecture III.-Delivered December 8th, 1892. The alterations which are taking place in the conditions under which coal gas may be used for illuminating purposes are so entirely dependent upon the adoption of the incandescent mantle as a means of developing light, that one of the most important questions to be discussed must of necessity be the relation existing between illuminating power, calorific value, and the light that can be evoked from the gas when burnt in an atmospheric burner by means of the incandescent mantle. At first sight there seems to be a wide discrepancy between observers on this point, and the literature of the past two or three years leaves one with a feeling of hazy uncertainty as to what relations really exist between the character of the coal gas and the light which the mantle will emit from it. on. Herr W. von Oechelhaeuser came to the conclusion from experiments made upon the Dessau gas that a reduction in the illuminating power of the gas causes an increase and not a decrease in the candle power of the Welsbach light. These experiments we will discuss later Some time later Dr. Bunte read a paper before the International Gas Congress in Paris, in which he pointed out that the changes in composition of gas, which reduce the illuminating power in flat flame and argand burners to a very great extent, have but little effect in producing differences in the illuminating duty of the Welsbach burner, and he showed by photometric measurements that the supplied in Berlin, Charlottenburg, gas Dessau, and Karlsruhe, although varying in illuminating value from 7.7 candles up to 109, gave, in spite of this relatively wide divergence in illuminating value, no difference in the light obtained from the mantles. He also showed that the calorific values of these gases was very nearly equal. A series of papers by Messrs. White, Russell and Travers, in America, gives the results of a research on the incandescent mantle and its behaviour, and they came to the conclusion that the light emitted by the mantle has little or no relation to the illuminating power of the gas when burnt per se as a luminous flame, and will increase almost directly with the nett calorific value, the increase being at the rate of 1 candle per cubic foot for every 4 calories increase in the nett heating value. I especially notice these three sets of observations, as in each case the work was carried out apparently with the necessary precautions that should be taken in securing accurate results. But there have also been a large number of experimental determinations made, in which neglect of such important factors as the regulation of the air supply in the burner and the initial gas pressure have led to still more chaotic results. In order fully to grasp this most important side of the question, and satisfactorily to determine the real effect produced, it is necessary to consider the factors which govern the atmospheric burner, and produce from coal gas the non-luminous flame which heats our mantle. In a lecture on the theory of the atmospheric burner which I gave before the Incorporated Gas Institute in 1897, I pointed out that the portion of the bunsen flame which heated the mantle, no matter what the composition of the original coal gas and the amount of hydrocarbons which it contained, if the burner were properly regulated as regards the air supply, consisted, as far as the combustible constituents went, of carbon monoxide and hydrogen, so that leaving out of the question the initial heat given by the incomplete combustion in the inner zone, water gas burnt without any admixture of air, would prove a highly successful method of developing light from the mantle. The chemical changes taking place in the flame of the atmospheric burner were first studied by Blochmann, whilst Prof. Smithells and I have of late years done considerable work on the subject. The actions taking place are perfectly clear. An ordinary 16 candle coal gas requires from 5.5 to 6 times its own volume of air for its complete combustion. If about half this volume of air is caused to mix with the gas before ignition at the burner head the gas is consumed in two stages which give the dual character to the flame, the inner cone being produced by incomplete combustion at the expense of the previously admixed air, whilst the outer cone is due to the combustion of the products of incomplete combustion from the inner zone, which takes place at the expense of the oxygen from the outer air. Such a flame, however, is not the best that can be employed for heating the incandescent mantle. If the air supply be further increased, the inner zone, in which the primary combustion is going on, shrinks in size and becomes green in colour, and in an ordinary atmospheric burner, such as is used in laboratories, any further increase in the air supply before combustion causes the flame to flash back to the bottom of the burner. But with various forms of burners for incandescent mantle heating, arrangements are made which prevent this, and the quantity of air can be still further increased. The popular idea of such burners as the Kern is, that practically the whole of the air needed for the combustion is mixed with the gas before it burns at the burner top. This, however, is an entire mistake, and if such a result could be obtained, it would defeat its own purpose. The best result is obtained from the incandescent mantle when a little over threequarters of the requisite quantity of air is mixed with the gas. This gives an inner zone of a bright green, which appears to seethe and boil on the gauze top of the mantle burner, whilst the products of incomplete combustion escaping upwards from this zone consist of It is this mixture escaping red hot from the inner zone which, in its combination with the oxygen of the outer air, excites the mantle to incandescence. If the aeration of the gas before burning is pushed beyond this point, the candle power yielded by the mantle falls instead of rising. Various theories have been put forward to explain the wonderful light emissivity of the incandescent mantle, the latest one being that of Messrs. White, Russell, and Travers, who conclude that the oxide of cerium is held in a state of solid solution by the oxide of thorium, and that this exerts a specific influence in altering wave lengths, so that the mantle emits more blue and green rays and fewer red rays, i.e., converts more of the energy of the flame into light and less into heat than does the ordinary flame that owes its incandescence to carbon particles. For my own part I do not agree with this, and am in entire accord with the theory of Professor Bunte that the process of combustion and the heat given thereby are stimulated by the catalytic action of the material of the mantle ; and I consider that Luggin's experiment, which showed that the Welsbach material can be brought by catalytic action in a cold mixture of gas and air to a state of full luminescence, to be conclusive evidence on this point. Taking these factors with regard to the condition of combustion as existing in the atmospheric burner flame, it is evident that the calorific value of the original gas will exert a certain influence on the temperature of the inner zone of the flame, and that the superheating action of this upon the combustible constituents of the escaping gas and the escaping products of combustion, will influence the temperature existing on and close to the surface of the mantle, so that, supposing the burner to be working under the best conditions of air supply, the light emitted will follow the calorific value of the gas. But the difference between the illuminating value given will only be a very small proportion of the difference between the calorific value of the two samples of gas. I showed in 1900 that the effect of the superheating influence of the inner zone upon the outer portion of the flame, is clearly demonstrated by using a Smithell's tube, by which the outer and inner zones of an atmospheric flame can be widely separated. Under these conditions, the superheating effect of the inner zone is reduced to a minimum, and a mantle heated in the outer zone gives but a poor light, whilst on allowing the inner zone to rise in the tube, the luminosity of the mantle increases, until, when it has resumed its normal position in the centre of the flame, the mantle emits its full light. It is clear from this that the superheating by the inner zone plays a part in the light emitted by the mantle. But in all the experiments I have made with gases of varying illuminating and calorific values, I have failed to find any alteration in the light yielded by the mantle that would justify the adoption of such a ratio of decrease as that given by Messrs. White, Russell, and Travers, i.e., one candle per cubic foot for a diminution of 4 calories, and I am forced to the conclusion from my own experiments that for calorific values such as mixed gases between 12 and 18 candle power possess, with proper air adstment to the burner the loss of light given by the mantle is so small as to be far overshadowed by the alterations in light due to inequality of shape in the mantle and other factors apart from the calorific value of the gas. The record of one experiment will show what I mean. A good mantle on a "C" burner was tested with a 177 candle power gas and gave 20.6 candle per foot of gas. 40 volumes of blue water gas were then added to 100 of the coal gas, and time given to complete the mixing of the two gases; on again testing under precisely the same conditions as before the mantle gave 177 candles per cubic foot of gas, and the light became a little unsteady. A collar was fitted to the air holes of the burner, and on regulating the air supply until the mantle gave the best results, a light of 20.1 candles per cubic foot was obtained. The details of the experiment are :— The pressure was 1 inches in each case, and the gas was burnt at the same rate of flow, i.e., 4 cubic foot per hour in both experiments. It is seen in this case that the loss of light given by the mantle was half a candle for a loss of flame illuminating value of 6.2 candles if tested by the 5 cubic feet rate, or 3.6 candles if tested in a rational manner. There was, moreover, a loss of calorific value in the gas equal to 33.5 calories. Therefore, according to the ratio given by Messrs. White, Russell, and Travers, the 2016 candles per cubic foot 33'5 ought to have been reduced by or 8.3 4 candles, so that 11.8 and not 20'1 candles should have been found. It is clear, therefore, that if care be only taken to properly adjust the burners, air supply, and mantles to the gas supply of a district, which could easily be done, the differences due to the lowering of the candle and calorific value of the gas become so small as to be negligible. To my mind this is a convincing proof of the truth of Dr. Bunte's catalytic theory of incandescence. If the light emitted by the mantle be due not so much to the temperature |