perception of these explosions;-and lastly, that the hearing will be strongly affected by introducing into the ears two probes, the opposite extremities of which are connected with the two ends of the apparatus. No effect has as yet been produced upon the sense of smell by this machine, which is ascribed to the circumstance of the electric effluvia not being expanded in and conveyed by the air, which it is thought is the proper vehicle for exciting sensations in the olfactory

nerves.

At the close of the paper the author points out the striking analogy there is between this apparatus and the electric organs of the torpedo and electric eel, which are known to consist of membranaceous columns filled from one end to the other with a great number of laminæ or pellicles, floating in some liquid which flows into and fills the cavity. These laminæ cannot be supposed to be excited by friction, nor are they likely to be of an insulating nature; and hence these organs cannot be compared either to the Leyden phial, the electrophore, the condenser, or any other machine capable of being excited by friction. As yet, therefore, they can only be said to bear a resemblance to the apparatus described in this paper. The effects hitherto known of this apparatus, and those which there is every reason to expect will be discovered hereafter, are likely, it is thought, to open a vast field for reflections and inquiries, not only curious but also interesting, particularly to the anatomist, the physiologist, and the physician.

Some Observations on the Head of the Ornithorhynchus paradoxus. By Everard Home, Esq. F.R.S. Read July 3, 1800. [Phil. Trans. 1800, p. 432.]

We learn from this communication that the beak of this singular animal, which on a cursory examination was thought to be exactly similar to that of the Duck, and calculated for the same purposes, is in fact materially different from it; and that, so far from being the mouth of the animal, as had been imagined, it is only a part added to the mouth, and projecting beyond it. This mouth has two grinding teeth on each side, both in the upper and lower jaw; they are without fangs, and may be considered as bony protuberances. Instead of incisor teeth, the nasal and palate bones are continued forwards, so as to support the upper portion of the beak; while the two under jaws are likewise continued forwards in the shape of two thin plates of bone, forming the central part of the under portion of the beak. The tongue is very short, and when extended can be projected into the bill scarcely one quarter of its length.

The organ of smell in this animal differs from that of quadrupeds in general, as well as of birds. The nostrils are nearly at the end of the beak, while the turbinated bones are situated in the skull, as in other quadrupeds; by which means there are two cavities the whole length of the beak superadded to this organ. The nerves which supply this organ are very large in proportion to the size of the animal.

Considering this curious structure of the nose in an animal which lives in water, it is natural to conclude that nature has fitted it for discovering its prey in that element, by means of the sense of smell; and that for this purpose it is enabled to introduce this prominence into the small recesses in which its natural food is probably concealed.

Experiments on the solar, and on the terrestrial Rays that occasion Heat; with a comparative View of the Laws to which Light and Heat, or rather the Rays which occasion them, are subject, in order to determine whether they are the same, or different. By William Herschel, LL.D. F.R.S. Part II. Read November 6, 1800. [Phil. Trans. 1800, p. 437.]

In the first part of this paper* the Doctor had proposed the seven following points which he meant to elucidate in this inquiry. 1. That heat, both solar and terrestrial, is a sensation occasioned by rays emanating from candent substances. 2. That these rays are subject to the laws of reflection. 3. That they are refrangible. 4. That they are of different refrangibility. 5. That they are liable to be detained in their passages through other bodies. 6. That they are also liable to be scattered on rough surfaces. And lastly, he proposed to ascertain whether in a certain degree of energy these rays may not have or acquire a power of illuminating objects. The three former points have been considered in the first, and the four last are the subjects of the present part of the paper.

Concerning the different refrangibility of the rays of heat, being the subject of the fourth article, we find that in refracting the rays of the sun by a prism, two distinct spectra may be said to be produced, the one of light, and the other of heat, the latter being distinctly observable by means of thermometers. These two spectra the Doctor has found means to represent by a figure, in which the length of the luminous or coloured spectrum, being represented by a line on which are raised ordinates proportionate to the quantity of illumination of each coloured ray, the curve joining these ordinates, together with this base line, inclose an area which may be said to represent the extent and intensity of the coloured rays. Adopting now another base line of the length of the range of the refracted rays of heat, one extremity of which is found to coincide with the termination of the coloured spectrum at the outward edge of the violet ray, and the other to project beyond the opposite termination at the red ray, which makes this line longer than the other, in the proportion of nearly 5 to 3. Ordinates are here in like manner applied according to the different degrees of intensity of heat indicated by accurate thermometers, and thus another area is produced, which represents the spectrum of heat both as to extent and intensity. On inspecting these figures, parts of which coincide, but other parts considerably deviate from each other, we find that the coloured and the heating rays differ widely, both in their mean refrangibility and

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in the situations of their maxima. And we also collect that the projecting part of the heating rays, being on the side of the red or least refrangible coloured ray, the aggregate of the former may be said to be less refrangible than that of the latter.

The Doctor now goes on to prove by experiments, that the sines of refraction of the heat-making rays are in a constant ratio to their sines of incidence, and points out the results of a correction of the different refrangibility of heat, by contrary refractions in different media.

Experiments are also described which show that the focus produced by a lens is in fact twofold, that which is produced by the rays of heat being in the same axis, but at some distance further from the lens than the luminous focus, a property that might have been inferred, à priori, from the less refrangibility of the heat-making rays.

In the fifth article, which treats of the transmission of heat-making rays through diaphanous bodies, besides the accurate description of the various apparatus which it was necessary to contrive for the purpose, and which can only be clearly understood by inspecting the figures added to the paper, we find the results of 170 experiments distinguished under the six following sections. 1. On the transmission of solar heat through colourless substances; through glasses of the different prismatic colours; through liquids, such as well and seawater, and different spirits; and through scattering substances, such as ground glasses, paper, linen, silk, &c. 2. On the transmission of the heat of terrestrial flame through various substances. 3. On the transmission of the solar rays, which are of an equal refrangibility with the red prismatic rays. 4. On the transmission of fire-heat through various substances. 5. On the transmission of invisible rays of solar heat. And lastly, (the subject which appears most pregnant with useful inferences for the common purposes of life,) on the transmission of invisible terrestrial heat. Not only the general position, that the rays of heat, both solar and terrestrial, are detained in their passage through various bodies, appears to be here completely evinced, but the great variety in the power of the transmitting bodies seems also to be determined with abundance of accuracy, and affords matter of much consideration and curiosity.

From the sixth article, in which it is intended to prove that the rays of heat, both solar and terrestrial, are liable to be scattered on rough surfaces, it appears that all bodies, even the most polished, are sufficiently rough to scatter heat in all directions. And the chief object of the twenty-four experiments here described, is to compare the effects of rough surfaces on heat with their simultaneous effects on light. The general and rather unexpected result is here brought forward, that colours have no concern whatever in the laws that relate to the scattering of heat.

The chief object of the whole of this inquiry follows next in the seventh article, where the question is discussed, "Whether light and heat be occasioned by the same or by different rays?" One of the leading facts deduced from the experiments in the fourth section, is that there are rays of heat, both solar and terrestrial, not endowed

with a power to render objects visible, and that there are different degrees of heat in the prismatic spectrum of these invisible rays. This being established, the question now, according to the original enunciation, is in fact, "Whether some of these heat-making rays may not have a power of rendering objects visible, superadded to their own already established power of heating bodies?" From a general and comparative view of those among the preceding experiments which apply to this question, we gather that no kind of regularity takes place among the proportions of the luminous and heating rays which are stopped in their passage, and that hence it might be reasonably inferred that heat and light are entirely unconnected. Yet, not to evade the above hypothesis, the Doctor enters into a more minute investigation of the subject, and shows that, admitting, according to the supposition, that the same rays being both luminous and calorific, may in their passage through certain media be so affected as to produce the very discordant results observed in the experiments, it is yet evident, on a due comparison of those results, that no given proportion that may be ascribed to this operation of the transmitting media, will anyways account for the general phænomena; the degrees of heat being in some instances greatly redundant, and in others as much deficient, both ways deviating from any given proportion. Thus it is that he reduces his opponent to the dilemma of either maintaining that the same agent may under different circumstances produce effects perfectly dissimilar, such as heat without light, decreasing heat and increasing light, or the reverse; or else to admit that there actually is a difference between the rays that give light, and those which produce heat.

A more direct proof of the difference of the two sorts of rays is deduced from the manifest results of the experiments, in which the stoppage of one sort of rays does by no means occasion the stoppage of the other sort. In investigating this subject the Doctor controverts a conjecture that the phænomena observed may be ascribed to a peculiar texture or configuration in the diaphanous substances, which produce differences in the transmission of the rays, though there be no difference in the rays themselves. This hypothesis also is minutely investigated, and its contradiction with the experiments being pointed out, its very foundation seems in fact to be wholly subverted.

Lastly, another direct proof of the difference of the two sorts of rays, is deduced from a comparative view of the results of some of the experiments, from which it appears that the stoppage of heat is in general gradually extending as far as five minutes in time, whereas the suppression of light hitherto appears to be instantaneous. This, together with various other arguments derived from the transmission of terrestrial heat, which cannot be properly explained in a manner sufficiently concise for this place, seem to evince that in fact the law by which heat is transmitted is essentially different from that which directs the passage of light, and that hence there is every reason to believe that the rays of heat are different from those of light.

An Account of the Trigonometrical Survey, carried on in the Years 1797, 1798, and 1799, by Order of Marquis Cornwallis, MasterGeneral of the Ordnance. By Captain William Mudge, of the Royal Artillery, F.R.S. Communicated by His Grace the Duke of Richmond, F.R.S. Read July 3, 1800. [Phil. Trans. 1800, p. 539.]

The mode of conducting this important survey having been already noticed in the Journals of the Society on various former occasions, it will only be necessary here to state the progress of the operation, which we find has now been carried on over Essex, the western part of Kent, Suffolk, and Hertfordshire, and portions of the counties contiguous to them. A distinct section contains the calculations of the sides of the principal and secondary triangles extended over the country in the three abovementioned years, together with an account of the measurement of a new base-line on Sedgemoor, and a short historical narrative of each year's operations. Another section contains the computed latitudes and longitudes of the places on the western coast intersected in 1795 and 1796, and also of such others since determined as lie conveniently situated to the newly observed meridians. Here we find likewise the directions of those meridians; one on Blackdown in Dorsetshire, another on Butterton Hill in Devonshire, and another on St. Agnes Beacon in Cornwall; as also the bearings, distances, &c. of the stations and intersected objects from the several ascertained parallels and meridians.

The Croonian Lecture. On the Irritability of Nerves. By Everard Home, Esq. F.R.S. Read Nov. 20, 1800. [Phil. Trans. 1801, p. 1.]

Its object is principally to investigate the opinion hitherto entertained, that the nerves may be considered as chords that have no power of contraction within themselves, but only serve as a medium by means of which the influence of the brain may be communicated to the muscles, and the impressions made upon the different parts of the body may be conveyed to the brain. After pointing out the extreme difficulty of such an inquiry, owing to the few opportunities that offer for investigating the real state of the nerves in the living body, Mr. Home intimates that he resolved to avail himself of every opportunity that might offer of any operation in surgery performed upon nerves, either in a healthy state, or under the influence of disease, in order to elucidate this intricate point, without neglecting certain experiments he thought he could devise upon animal bodies, before they are wholly deprived of life.

The first case, which explains some circumstances respecting the actions of the nerves when under the influence of disease, was that of a middle-aged person, who, having hurt his thumb by a fall, experienced long after an occasional swelling and convulsions in that part, attended with spasms, which at times extended in the direct course of the trunks of the radial nerve up to the head, the patient being at times afflicted with absolute insensibility. In order to put a stop to

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