The bearing which the subject of the following communication has upon the much-vexed question of the unity of the human species, and the inferences which may be drawn from it in relation thereto, invest it with an importance which would not otherwise belong to it.

The position which the question I allude to at present occupies is this. On the one hand, the advocates of the view that all men are not of the same species, but that they compose a genus consisting of many species, maintain that the parasites which infest the different races of man are distinct; and because we usually find that distinct species of parasites are allotted respectively to the different species of the lower animals, they infer that the same rule must hold with man, and that therefore each different race possessing a distinct parasite must be a distinct species.

By means of my correspondents abroad, and more particularly through the kind offices of Dr Christison, I have been enabled from time to time to cultivate in the Botanic Garden some of the rarer plants of the Materia Medica. Several of these, such as the Jalap plant, the Quassia, and the Aconitum ferox, have been already described and figured by me. The present is an interesting addition, and at the suggestion of Dr Christison I have brought it under the notice of the Royal Society.

1. The first part of this paper describes the following groups of experiments:—

Group I. On the effect which roughening the surface of a body produces upon its radiation.

II. On the nature of that heat which is radiated by rock-salt, at 212°F.

III. On the radiation of glass and mica, at high temperatures.

The second, or theoretical portion, of the paper, has reference to the law which connects the radiation of a particle with its temperature, and to Dulong and Petit's experiments on this subject.

There is also an addition of a later date than the rest of the paper on General Diathermancy.

1. To find the numerical law according to which the temperature of a place varies with its latitude, is an empirical problem which has, since the middle of the last century, from time to time engaged attention.

2. Lambert, Mayer, and Kirwan in the last century, De Humboldt, Brewster, Kämtz, and Dove in the present, may be cited amongst those who have investigated formulæ which express, with more or less accuracy, the mean temperature of a place in terms of its latitude.

3. The formulæ proposed are mostly reducible to two types—a variation depending upon the cosine of the latitude simply (that of Sir D. Brewster), and one depending on the square of the same quantity (that of Mayer).

The excursion described in the following pages was planned by Dr Macpherson, Inspector-General of Hospitals, and myself, with a view to explore the Southern Range of the Anamalai (i.e. Elephant Hills), in the district of Coimbatore, which are sparingly laid down in the Great Trigonometrical Survey Map, while the peculiarities of their Fauna and Flora had not been recorded.

The project was approved by the Right Honourable Lord Harris, then Governor of the Madras Presidency, and the services of Major D. Hamilton were sanctioned by His Excellency Sir Patrick Grant, Commander-in-chief, to accompany us as artist, to delineate the characteristic features of the country.

The constitution and properties of the essential oils attracted considerable attention during the earlier period of the investigations in organic chemistry, and several of them have contributed in no small degree to the development of the general doctrines of that department of the science. A majority of these substances, however, may be said to be still almost unknown, all the information we possess regarding them being restricted to a single analysis, made on what was obviously a mixture, or to a few observations of a general and often indefinite character. The complex nature of many essential oils, and the want of experience and easy processes for the separation of their constituents, have hitherto deterred chemists from attempting their minute examination, but the progress of the science has increased our knowledge of the methods of investigating these substances, and renders it important that their true constitution and position in the chemical system be definitely fixed. With this object I have taken up the investigation of Oil of Cajeput; our information regarding which is confined to a single analysis made by Blanchet and Sell, some five and twenty years ago.

In this paper I shall first refer to the circumstances under which the following observations were made.

I had gone in the autumn of 1856 for a few weeks to Elie on the Fife coast, and was induced, as a means of relaxation and exercise in the open air, to pay some attention to the geology of the neighbourhood, resuming for a brief interval what was once a favourite pursuit. About a mile to the east of the village, I found a stratum well deserving attention—a thin bed of limestone—dipping inland a little beyond the cliff on which stands the ruined Castle of Ardross. The fossil shells which it contained were of unusual form, and beautifully preserved; there were fish remains of two or three species, and a small group of crustaceans still more remarkable. Among the fish I thought I could detect the large scales of an Irish species—the Holoptychius Portlockii—and among the crustaceans there were the valves of Dithyrocaris, a genus particularly characteristic of the Irish beds. At once the question arose whether these fossils might not serve as links connecting this Ardross bed with the Irish series. The point was of the more importance, that our leading geologists had been differing widely as to the true position of our Scottish coal strata in the geological scale. The lamented Professor Edward Forbes had assigned them a place comparatively high, while Sir Roderick Murchison, with surer judgment, had taken the opposite view and put them beneath the Newcastle coal-field.

Sir Thomas Brisbane was born at Brisbane House, Largs, on the 23d July 1773. He was descended from the Brisbanes of Bishopton, one of whom, according to Hailes, “held the office of Chancellor of the kingdom of Scotland in 1332.” They possessed a large tract of country, extending from Erskine Ferry to Largs; and had this estate been still in their possession (consisting, as it did then, of Bishopton, Greenock, Ardgowan, Skelmorlie, Largs, and Brisbane), its revenues would have been princely; but Sir Thomas only inherited the smaller portion of the possessions of his ancestors, Largs and Brisbane.

The following Memoir contains the results of researches made during the last three years. My investigations were originally directed to British lichens only, but they have subsequently and gradually embraced lichens from all parts of the world. The majority of Scotch species examined were collected by myself while on botanical tours in various parts of Scotland during the last ten years. Lowland species were collected chiefly in the counties of Perth, Edinburgh, and Dumfries; but also in Forfar, Fife, and others of the midland counties. In order to study alpine species I made a special tour among the highest of our Scotch mountains in the summer of 1856. I then visited the Braemar Highlands, Ben Lawers, Ben Nevis, and the Coollin Hills, in Skye. I have likewise studied the lichens of Don, now in the possession of Mr M'Nab, of the Ptoyal Botanic Garden, Edinburgh; the lichens collected by Maughan, M'Millan, and others, in the Herbarium of the Botanical Society of Edinburgh; those collected by the late Alexander Menzies, in the Menziesian Herbarium belonging to the Botanic Garden of Edinburgh; those collected by Borrer, Hooker, Carmichael, Gardiner, and others, in the magnificent Hookerian Herbarium at Kew; and I have also examined the valuable herbarium of the University of Edinburgh, under the care of Professor Balfour, and the herbarium of Dr Greville.

1. Every purely periodical function is, as is well known, expressible by means of a series of constant coefficients multiplying sines and cosines of the independent variable with a constant factor and its multiples. This important truth was arrived at by an admirable piece of mathematical analysis, called for by Daniel Bernouilli, partially given by La Grange, and perfected by Fourier.

In a paper on the Polarisation of Light by Refraction, published in the “Philosophical Transactions” for 1814, I have shown that when a pencil of light is incident on a number of uncrystallised plates, inclined at the same or different angles to the incident ray, all their surfaces being perpendicular to the plane of the first incidence, the transmitted pencil will be wholly polarised, when the sum of the tangents of the angle of incidence upon each plate is equal to a constant quantity, depending upon the refractive power of the plates and the intensity of the incident pencil.

A few years since I was engaged in the performance of some calculations under the direction of Professor W. Thomson of Glasgow, having reference to the observations of underground temperature made at the Royal Edinburgh Observatory. In this paper I propose to describe a modification of Professor Thomson's method, which, while retaining a sufficient degree of accuracy, will be simple enough for general adoption. The objects proposed are—

1st, To express the variations of temperature at a given depth in terms of the time of year.

2d, To deduce the conducting power of the soil.

Some years ago I commenced an examination of the behaviour of the so-called olefines towards certain compound halogens. I was induced to this by the conviction that the bodies resulting from the union of a group of unequally chemico-negative elements with an olefine, would place an instrument of great power into the hands of systematic chemists, especially of synthesists. My expectations have been more than realized. The few olefines which I have examined in their relation to compound chemico-negative groups have given rise to a series of new bodies remarkable alike for their great number and for the elegance and importance of the reactions attending their formation and recompositions.

In the Geology of Scotland, no feature comes at once more prominently before the observer than the number and variety of the trap-rocks. From the Sheant Isles to the Cheviot Hills the map is dotted over with trappean patches, which occur sometimes as long, narrow dykes, and often as irregular sheets, that extend almost over entire counties. The appearance of the rocks on the face of the country is scarcely less marked than on the map, and to their ever-changing varieties, we owe not a little of the characteristic scenery of Scotland. Throughout the wilds of the Inner Hebrides it is the trap-rocks which form many of the precipitous cliff-lines, and the craggy irregular hills. The soft pastoral valleys of the Ochils and the Pentlands lie among trappean rocks, while the hill-ranges, which break up the great central valley of Scotland, more especially the abrupt solitary crags that form such prominent landmarks, owe their existence to the permanence of the trap-rocks of which they consist. In short, there is no group of rocks more constantly found throughout the length and breadth of the island, and none, therefore, which so frequently obtrudes on the geologist or more imperatively demands his attention.

If it be true that “there is a history in all men's lives, figuring the nature of the times deceased,” how much more worthy of record the lives of those who have left an impress upon their age, who have corrected popular errors, have made clear much that was obscure, and, from the force and fulness of truth in them, have become the great teachers of their time. The histories of such lives figure more than the “times deceased,”—they teach us how to occupy our time; and though these earnest men are dead, their works are yet living epistles, ever speaking to those “who have ears to hear.”

The solid compounds of carbon and hydrogen form a class of substances to which chemists have scarcely, as yet, paid that attention which their importance and interest appear to merit. With the exception of naphthaline, very little is known regarding them, and it is remarkable that the numerous and varied products of decomposition obtained from that singular substance should not have induced a more minute examination of the kindred compounds, whose existence has been indicated by different chemists. The interest attaching to these compounds is all the greater because, according to their discoverers, several of them are isomeric, or at least polymeric, with naphthaline; and a more careful examination of them might be expected to throw some light on their intimate constitution, and relations to that body.