1. This paper consists of two parts, the first of which is confined to describing the experiments performed; while in the second it is attempted to connect these with certain theoretical views regarding Radiant Heat.

2. The experiments were made with a fourfold object; at least, for the sake of clearness, it is well to class them into four distinct groups:—

Group I. Contains those experiments in which the quantities of heat radiated from polished plates of different substances, at a given temperature, are compared with the quantity radiated from a similar surface of lamp-black, at the same temperature.

II. Those in which the quantities of heat radiated at the same temperature, from polished plates of the same substance, but of different thicknesses, are compared with one another.

III. Those in which the radiations, from polished plates of different substances at any temperature, are compared with that from lampblack at the same temperature, with regard to the quality or nature of the heat radiated.

IV. Those in which the same comparison is made between the radiations from polished plates of the same substance, but of different thicknesses.

It has been long known that in various parts of Africa, the natives are in the habit of subjecting to the ordeal of poison parties who are suspected of crimes. On the east coast, we meet with Tanghinia venenata, yielding the Tanghin poison-nut of Madagascar; and on the west coast, seeds and barks of different kinds have been employed as ordeals,—the sources of which, however, have not been hitherto fully ascertained.

Dr Kirk, naturalist to the Livingstone Expedition, states, that the Manganja tribe, in the south-east of Africa, believe in a God, and in medicine, or the ordeal which he directs as the means of discovering crime. If the ordeal causes vomiting, it shows innocence; if it acts by the bowels, crime, and the person is put to death. But the doctors have a good knowledge of which to give, for there are different plants used.

The interest awakened by Gay-Lussac's great discovery of the simplicity in the relation of the volumes of gases has greatly increased in recent times, when chemists have discovered that, in a large number of instances at least, the formula of a body, as deduced physically from its vapour density, exactly coincides with that deducible from chemical considerations of its reactions, and from the nature of the products arising in consequence of them.

The processes at present used for determining the vapour densities of bodies, are those of Gay-Lussac and Dumas.

If we examine the flame arising from the combustion of any of the hydrocarbons, such as that of coal-gas, or of a common candle, it will be found to consist of several portions easily distinguishable by the eye, and in which the matter composing the flame exists in very different conditions. There is, first, a central non-luminous region, in which the gases are not yet ignited; secondly, a blue conoidal envelope, extending from the wick or burner, and gradually thinning out towards the top of the flame; thirdly, a more or less luminous conoid, thin towards the bottom of the flame, where it is enveloped by the blue conoid, but thicker towards the top. And fourthly, a faintly luminous outer envelope, completely surrounding the other portions of the flame, and greatly developed towards the top.

In 1845, a paper by me on the balance magnetometer was read to the Royal Society of Edinburgh (see Trans. vol. xvi. p. 67), which contained an examination of some of the difficulties to be considered and overcome in relation to that instrument. No similar examination has yet appeared, as far as I am aware, of the bifilar magnetometer. When it is considered that the value of the results obtained from this instrument in so many observatories is dependent on an exact knowledge and elimination or correction of its errors; and, as will appear hereafter, that the temperature coefficients employed in the discussion of the Colonial observations are in some cases so erroneous that the unconnected observations would have been nearer the truth than after correction, the following communication may not appear unnecessary.

In a former communication to the Royal Society of Edinburgh, I gave an account of an unusual fall of rain in the Lake District in the month of January last year. That occurrence was followed by its opposite in May, June, and July; not for a long period, not since 1826, has the district suffered more from want of water than in those months.

This drought is best shown by the following table, in which will be found the rain-fall for the several months of the year at five different places, only a few miles remote from each other. The table will also show the remarkable contrast as to excess and deficiency of rain during the period. It may be premised, that at Ambleside, where the drought appears to have been felt as much as anywhere, the ordinary fall of rain for the months in question is about three times as great; thus for May (our driest month of the twelve), taking the average of the preceding eleven years, it is 2·37 inches, for June 4·22 inches, for July 5·27 inches, making a total of 12·36 inches, against 4·54 inches of the months of drought.

In the writings of comparative anatomists, considerable difference of opinion is expressed respecting the position and relations of the thyroid gland in the Cetacea, and some authorities even have asserted that it does not exist in these Mammalia.

John Hunter states that he has examined several porpoises, balænæ, and other cetacea, yet “could not observe anything like a thyroid gland.”

Meckel believed that he found, in a fœtal porpoise (D. phocœna), eight inches long, a thyroid gland. He describes it as half an inch broad, two lines thick and high, and of equal depth and thickness both on the middle and sides of the air-tube, in the same position as that in which the gland is found in other mammals. From this examination, however, of so young a fœtus, he does not feel disposed to affirm that, contrary to the opinion of Hunter, it exists in full grown cetacea. In a subsequent paper he mentions incidentally, that in the dolphins the gland is formed of two quite separate lobes. Cuvier states that he has found the gland very distinct in many dolphins and porpoises. In these animals it was divided into two parts, and suspended from the trachea opposite the upper border of the sternum, and some distance from the larynx. Carus describes the gland in the dolphin and porpoise as consisting of two parts, entirely separate from each other. It is difficult to say, however, from the text, whether he is giving the result of his own observations, or simply adopting those of Cuvier. Dr Martyn repeats the statement that the cetacea do not possess a thyroid, and he ascribes the supposed absence of the voice in these animals to the want of this glandular structure.

In 1849 I presented to the Royal Society of Edinburgh a paper “On the Gradual Production of Luminous Impressions on the Eye.” The object of that communication was to investigate the laws of the production of visual impressions. The subject was then new; for although the fact that light requires a certain time to produce its full effect on the eye had been noticed at comparatively early periods, yet no one, so far as I am aware, had attempted to measure that time; and the whole subject of the production of visual impressions, regarded as a branch of experimental science, was quite untouched. I have frequently wished to resume a subject of inquiry which seems to me to merit more attention than it has hitherto received, and which I have not as yet been able to discuss so completely as I could have desired. Various portions of it demand more extended experiments. Among these may be specified, the examination of isolated impressions of shorter duration than my limited instrumental means had enabled me to observe; a more careful determination of the time required for light to produce its complete effect on the eye; and a series of observations on the eyes of various individuals, so that any personal peculiarity of vision, which might affect results derived exclusively from experiments on my own eye, might be eliminated. These, and other subjects of inquiry, I hope sooner or later to overtake; and, indeed, I had anticipated before the end of the present session of the Society to have been able to obtain some experimental results. In this I have been disappointed, owing to the instruments required for my observations having taken a much longer time to make than I had expected.

These notes have been made at different intervals of time, and in different places,—some, and the majority of them, in Malta, in 1832–33,—some at Constantinople in 1839–40, and a few at a still earlier period, viz. in 1816, when on a voyage to Ceylon.

Imperfect and brief as many of them are, I am induced to submit them to the Society, thinking they may be of some use as conveying the results of unbiassed observation, and that, as such, they may prove a small contribution, to a difficult branch of icthyology,—difficult, not indeed so much from the nature of the subject as from the comparatively few opportunities enjoyed by naturalists of obtaining specimens.

Amongst the natives of Ceylon, the occurrence of the Albino, the offspring of dark-skinned parents, is not very uncommon. In looking over my note-books, kept whilst I was in that island, between the years 1816 and 1820, I find mention made of five several examples. Now that the subject of species and varieties is attracting so much attention, perhaps the particulars I then collected of these abnormal instances of the human race may not be altogether without interest, even if given a little in detail.

1. The late Mr Alexander Adie, optician, and Fellow of the Royal Society of Edinburgh, was so generally known to be a zealous and careful observer of meteorological instruments, that an attempt to combine the results deducible from his labours carried on (though with one long break) over more than forty years, cannot be otherwise than interesting.

2. The plan of superintending the careful reduction of the thermometrical part of Mr Adie's registers occurred to me a long time ago, but circumstances prevented the execution of it until two or three years since, when, through the kindness of Mr Adie and his family, the whole of the manuscript observations, commencing with 1795, were put into my hands, and the Council of the Royal Society of Edinburgh provided sufficient funds for the employment of computers for reducing them.

3. The work has proceeded with frequent interruptions, but is at length complete. Before I proceed to detail the particulars of the reductions and their results, I will give a short account of the earlier observations on the climate of Edinburgh which I have been able to trace, some of which perhaps have hitherto escaped notice.

The rain experienced in January of this year has so much exceeded the average quantity, considerable as that is in the Lake District, that I have been led to consider it worthy of record, especially keeping in mind, that as regards risks from floods, it is not the ordinary, but the extraordinary that is to be guarded against in the construction of all works with which water is concerned as an element of danger.

It may not be amiss to premise, that the year preceding, as to weather, was chiefly remarkable for the mildness of the first quarter, for its high summer temperature, for the unusual cold experienced in November, and this succeeded by a mild December. January set in with weather of the same character, and was without any marked peculiarity, excepting its mildness, till the 9th, when rain commenced, and, with the exception of two or three days, continued to fall more or less heavily till the end of the month.

The only observations made with Dr Lloyd's bifilar magnetometer, published with corrections applied to the individual observations, are those made in the Makerstoun Observatory, forming part of the Transactions of the Royal Society of Edinburgh. The results obtained from these observations (especially from those for 1844 and 1845), were first compared by me in 1856, with observations (also corrected by myself) made in the Trevandrum Observatory during the same years. The singular resemblance of the variations of daily mean intensity thus discovered at two places so distant, and so differently situated on the earth's surface, induced me to undertake the considerable labour of determining the temperature coefficients, and of correcting and discussing all the published (and some unpublished) observations made in the colonial observatories. This labour was too great to have been undertaken by me alone, in consistence with my other duties, and it is due to the liberality of His Highness the Rajah of Travancore, that I could employ in part for this work the computers attached to his Observatory.

1. When I found that the interesting meteorological register of Mr Adie, which is well fitted to throw light upon the climate of Edinburgh, and of Scotland generally, was deficient of the important period of nearly sixteen years, from 1805 to 1820, I set on foot inquiries as to the existence of any other register of the thermometer which might approximately supply the defect. After some unsuccessful attempts, my attention was directed by Professor Dove's useful temperature tables to a register of the thermometer kept by the Rev. Mr Fergus of Dunfermline, of which the monthly means, from 1805 to 1824, are given in the “Edinburgh Philosophical Journal,” vol. xiii. Though the distance of Dunfermline from Edinburgh is thirteen miles in a right line, and though it occupies the opposite slope of the valley of the Forth, not far from the Ochil Hills, yet a slight comparison of the observations showed a very remarkable coincidence in its climate with that of Edinburgh, not only as regards the mean annual temperature, but also in the distribution of temperature throughout the year. I therefore made an effort to obtain the original register from which the results published in the “Edinburgh Philosophical Journal” were derived; and through the kindness, in the first instance, of Mr David Laing of the Signet Library, I was brought into communication with the Rev. John Fergus of Bower, near Wick, in Caithness, son of the Dunfermline observer, who most kindly placed in my hands his father's original register of the barometer, thermometer, and weather at Dunfermline, extending from 1799 to the time of his death in 1837, all made with one instrument, and at the same hour daily (9 a.m.), with very remarkable regularity.

In a recent work of an elaborate kind, displaying much ability, its author, Dr Richardson, has endeavoured to prove that the cause of the coagulation of the blood is of a chemical nature, and referable to the escape of a volatile matter, and that the volatile matter is ammonia.

It is not my intention at present to consider the various circumstances which he brings forward in favour of his conclusion. I shall restrict myself to a few observations which I have made, the results chiefly of trials instituted for the purpose of testing his speculations, and of satisfying myself, if possible, on the subject.