a stream of air driven through a pipe with a lateral aperture, like a French flute, where at the part where the stream issues out of the orifice, vibrations are manifestly perceived, which are rendered still more evident if the current be impregnated with smoke.

4. Of the Velocity of Sound.-The velocity of any impression transmitted by the common air, being corrected by the experiments of various observers, is at an average here estimated at 1130 feet in a second of time.

5. Of Sonorous Cavities.—What is here said relates chiefly to the reflection of sounds in rooms or galleries. This we find takes place as often in a second as double the breadth of the room or passage is contained in 1130 feet, that breadth determining the pitch of the musical note thereby produced.

6 Of the Divergence of Sound.-Various observations are here related which militate against the received opinion that sound diverges equally in all directions, and that there is no substance impervious to sound. On this head, however, the author admits that a more ample investigation will be required than has hitherto been instituted; and he intimates that he shall engage in it as soon as his leisure will permit.

7. Of the Decay of Sound.-The two hypotheses, 1st, that sound decays nearly in the simple ratio of the distances, and 2nd, that this diminution is in the subduplicate ratio, are here stated, and some fallacies are mentioned, which will likewise render a further inquiry necessary.

8. Of the Harmonic Sounds of Pipes.-The object of this section appears from a table exhibiting the results of a set of experiments, made with a view to ascertain the velocity with which organ-pipes of different lengths require to be supplied with air, according to the various appropriate sounds which they produce.

These were made on pipes of the same bore, and of different lengths, both stopped and open. The general result was, that a similar blast produced as nearly the same sound as the length of the pipe would permit, or at least that the exceptions, though very numerous, lie equally on each side of this conclusion.

9. Of the Vibrations of different Elastic Fluids.—The difference of these vibrations has been received as being reciprocally in the subduplicate ratio of the density of the fluid. Hence in pure hydrogen gas they must be 3.6 times greater than in common air. And this will explain why an instrument will often appear out of tune, when, in fact, the fault lies in the change of temperature of the atmosphere; and why the pitch of an organ will be found to differ materially in summer and winter.

10. Of the Analogy between Light and Sound.-While the author vindicates the Newtonian theory of light against the criticisms of Euler, he freely admits that it is liable to some objections, among which he chiefly insists upon the uniformity of the motion of light in the same medium, and the partial reflection from every refracting surface. Having reasoned largely upon this subject, he admits the

probability of an analogy between the colours of a thin plate and the sounds of a series of organ-pipes; and observes that the same colour recurs whenever the thickness of the plate answers to the terms of an arithmetical progression, in the same manner as the same sound is produced by means of an uniform blast from organ-pipes which are different multiples of the same length.

11. Of the Coalescence of Musical Sounds.-In this section Dr. Smith's assertion that the vibrations constituting different sounds are able to cross each other in all directions, without affecting the same individual particles of air by their joint forces, is minutely investigated and controverted.

12. Of the Frequency of Vibrations constituting a given Note. 13. Of the Vibrations of Chords.

14. Of the Vibrations of Rods and Plates.

Of the contents of these three sections no account will be here attempted, as they consist chiefly of experiments and demonstrations illustrated by diagrams.

15. Of the Human Voice.-A technical description is here given of the formation of sounds by the configuration and inflexions of the different parts of the vocal organ. And it is intimated that by a close attention to the harmonics entering into the constitution of various sounds, much more may be done in their analysis than could otherwise be expected.

16. Of the Temperament of Musical Intervals.—After pointing out some imperfections in most of those who have treated this subject before him, the author suggests his own method of distributing the imperfection of the scale, so as to produce a modulation that shall be found the least defective. And here he observes, as upon an average of all music ever composed some particular keys occur at least twice as often as others, there seems to be a very strong reason for making the harmony the most perfect in those keys which are the most frequently used; since the aggregate sum of all the imperfections which occur in playing, must by this means be diminished the most possible, and the diversity of the character at the same time accurately preserved.

Observations on the Effects which take place from the Destruction of the Membrana Tympani of the Ear. By Mr. Astley Cooper. In a Letter to Everard Home, Esq. F.R.S., by whom some Remarks are added. Read Feb. 6, 1800. [Phil. Trans. 1800, p. 151.]

The case to which we owe the observations contained in this paper, is that of a youth, who at the age of ten was attacked with an inflammation and suppuration in the left ear, which continued discharging matter for several weeks; and who after the space of about a twelvemonth had the same symptoms in his right ear, the discharge in both cases being thin and fetid, and conveying many small bones and particles of bones. On probing the ears when the youth was about twenty years of age, it was found that the membrana tympani

of the left ear was totally destroyed, and that but a small part of it remained in the right ear. So free was the passage through both the ears, that the patient, by closing his nostrils and contracting his cheeks, could with ease force the air from the mouth through the meatus auditorius; and yet what is most remarkable, the sense of hearing was by no means materially impaired by this imperfection; especially in the left ear, where the whole of the membrane was dissolved. The organ even retained a nice musical discrimination.

From this, and another similar instance here described, it is inferred that the loss of the membrana tympani, though it somewhat diminishes the power of hearing, does not absolutely destroy it; and that probably where this membrane is wanting, its functions are supplied by the membranes of the fenestræ ovalis and rotunda, which being placed over the water of the labyrinth, will, when agitated by the impressions of sound, convey their vibrations to that fluid, in a similar manner as is done by the membrana tympani in its healthy state. It is also intimated that the principal use of this membrane is probably to moderate the impressions of sound, and to proportion them to the powers and modifications of the organ.

Mr. Home, by whom this paper was communicated, has been pleased to add some additional remarks on the mode of hearing in cases where the membrana tympani has been destroyed; from which we collect that this membrane appears to him to be chiefly intended to give an extended surface capable of communicating to the small bones the impressions made upon it, which a membrane would be incapable of doing unless it had a power of varying its tension to adapt it to different vibrations: and that this membrane being destroyed, there can be little doubt that the impressions of the vibrating air are produced on the stapes, from whence they are communicated to the cavity of the tympanum, and thence to the internal organ. These remarks are added in order to reconcile the present case with the doctrine laid down by Mr. Home in his late paper on the organ of hearing.

Experiments and Observations on the Light which is spontaneously emitted, with some degree of Permanency, from various Bodies. By Nathaniel Hulme, M.D. F.R.S. and A.S. Read Feb. 13, 1800. [Phil. Trans. 1800, p. 161.]

The light which is the object of the present inquiry must be distinguished not only from that which we derive from the sun, but also from the brightness exhibited by artificial phosphori, electricity, meteors, and other lucid emanations. The principal bodies which afford the light here treated of, are, 1) Some vegetable and earthy substances, such as rotten wood, and peat earth. 2) Marine animals, some in a living state, viz. the Medusa phosphorea, the Pholas, the Pennatula phosphorea, and the Cancer fulgens; and most of the marine fishes soon after they are deprived of life. 3) Animal flesh in general, some time after the extinction of life. And, 4) Among

insects, the creeping glow-worm, the flying glow-worm, the fire-fly, and the great lantern-fly.

The numerous experiments described in this paper were chiefly made on marine animals, particularly herrings and mackerel, which were exposed either in the air, or in water impregnated with different salts, and of different temperatures, in a dark vault to which the Doctor assigns the name of his laboratory.

The results obtained in this investigation are described in nine sections, the summary contents of which are as follows:

1. The quantity of light emitted by putrescent animal substances does not arise from the greater degree of putrefaction in such substances, as is commonly supposed; but, on the contrary, they begin to shine some time before any apparent signs of putrefaction take place, and the greater the putrescence, the less is the quantity of light emitted.

2. Light is a chemical element, or a constituent principle of some bodies, and particularly of marine fishes; and it may be separated from them by a peculiar process, or be retained, and rendered permanent for some time. The experiments from whence this inference is derived were made with pieces of herrings and mackerel, and with living tadpoles immersed in solutions of Epsom salt, sea salt, Glauber's salt, and in all which a quantity of light was manifestly imparted to the saline menstruum, which the latter under various circumstances retained for a considerable time. These experiments seem also to evince, that light is not partially but wholly incorporated with every particle of the animal substance; that it is probably the first elementary principle that escapes after the death of fishes; and that as the putrescence was by no means promoted, but rather retarded by this emission of light, it is highly probable that no offensive putrefaction ever takes place at sea after the death of such myriads of animals as must needs daily perish in the vast ocean, which hence continue long a wholesome food to the many kinds of fish that feed upon their congeneries.

3. Some bodies or substances have a power of extinguishing spontaneous light when it is applied to them. These are water, both pure and impregnated with quick lime, carbonic acid gas, and hepatic gas, fermented liquors, ardent spirits, fixed and volatile alkalies, certain neutral salts, vegetable infusions, pure honey, and the rust of iron, calamine, minium, and manganese dissolved in water.

4. Other bodies or substances have a power of retaining spontaneous light for some time when it is applied to them. These substances are most of the solutions mentioned in the second article, which, when impregnated with some of the lucific matter scraped from herrings and mackerel, retain the light for some days, especially if assisted with some agitation of the phial containing them. The appearances here exhibited are described as being both beautiful and surprising, as they enable us to take light from one substance and transfer it to another, so as to render the latter most brilliantly luminous; or in other words to impregnate a liquid with light.

5. When spontaneous light is extinguished by some bodies or substances, it is not lost, but may be again revived in its former splendour, and that by the most simple means.

These means are in general the greater or less degrees of impregnation of the saline menstrua, which alternately extinguish and revive the light at the option of the operator.

6. Spontaneous light is not accompanied with any degree of sensible heat, to be discovered by a thermometer.

7. Cold extinguishes spontaneous light, but not permanently, as the substances mentioned in the third article; since here the light could be revived in its full splendour, by exposing the substance to a moderate degree of temperature.

8. The eighth section treats of the effects of heat on light when in a state of spontaneous union. We gather from the experiments here described, that in every substance there is a certain point of temperature at which it acquires its maximum of lustre; that this varies considerably in various substances, the fishes, rotten wood, and aqueous solutions, becoming dark at a temperature of between 96° and 110°; while glow-worms retain their lustre until exposed to the degree of boiling water. Common water impregnated with light, when by mere time and rest, without any considerable change of temperature, it had become obscure, was soon rendered luminous when gradually warmed by small and successive additions of warm water; but no sooner was boiling water added in any considerable quantity, than the luminous appearance vanished, and was altogether extinguished.

It was here observed, that if heat be applied to the bottom of a tube filled with illuminated water which has been some time at rest, the light will descend in luminous streams from the top of the tube to the bottom, and be gradually extinguished.

9. In the ninth and last section we find a set of experiments on the effects of spontaneous light when applied to the human body. As to the living body, it was found that on touching the luminous matter of fishes, the light adhered copiously to the fingers and different parts of the hands, remained very lucid for some time, but then gradually disappeared; whereas the same kind of matter being applied to pieces of wood, stone, and the like, of the same temperature as the laboratory, continued luminous on these substances for many hours. It might hence be inferred that the living body ultimately absorbs the light; but other experiments seem to contradict this inference, it having been observed that a piece of shining wood being placed on the palm of the hand, and a glow-worm being breathed upon repeatedly, were both rendered more luminous, and this for a considerable time.

As to the animal fluids; the crassamentum of the blood of healthy persons, and also of some labouring under inflammatory diseases, received indeed the light of a herring to a certain degree, but did not retain it long: and when this coagulum had been kept for some time,