230. I have records of observations made on April 11 and May 11, 1867, in which I expressly state that I could not detect any object on the surface of Linné. With Mr. Barnes' silvered glass reflector (With) I very carefully examined Linné, on the 10th of June, 1867; but although both Mr. Barnes and Mr. Browning saw a white nucleus, I was unable to detect it, and saw nothing of a crater of the magnitude of 4" 0, which I think I must have seen, had it been there.

With regard to the variations in the extent of the whitish cloud, I have observed phenomena of the same kind on the Mare Crisium, and about seventy sets of measures of Dionysius, yield the same result, though not to so great an extent as in the case of Linné.

OBSERVATIONS ON LINNÉ.

BY WM. HUGGINS, ESQ., F. R. S.

In " Monthly Notices" Mr. Huggins publishes a view of Linné, as seen by him on May 11, at 8h. 45m. It represents Linné as an oval white spot, and to the west of its centre shows a white ring surrounding a black spot. Mr. Huggins remarks, "At the time when the diagram was made, the shallow, saucer-like form of Linné was not seen; but I have detected it on other occasions. June 8, at 7h., when a great part of the light reflected from our atmosphere was removed by means of a Nicol's prism, I observed a shadow within the eastern margin of this shallow crater. When the diagram was taken, on May 11, the "interior of the small crater was in shadow, with the exception of a small part of it towards the east. The margin of the small crater was much brighter on the western side, and at this part appears to be more elevated above the surface of Linné. Under a very oblique illumination this high eastern wall appears as a small bright eminence, and casts a somewhat pointed shadow."

On the 9th July, at 9, Mr. Huggins measured Linné, and found the

Length of the bright spot
Breadth

Diameter of small crater

The power employed was 500.

On the 14th Feb., 1866, Mr. Huggins examined the spectrum of the light from Linné, but could detect no lines not belonging to solar light.

Mr. Huggins quotes Schröter's description of Linné, and remarks that in Plate IX. of his "Selenotopographische Fragmente," "the place occupied by Linné is marked by

a round white spot, and not by the figure of a crater." Schröter's words are, 66 'Als ein weisses sehr kleines rundes Fleckchen erscheinende, etwas ungewisse einsenkung in sich hat ;" which may be translated, "Appearing as a white, very small round spot, with a somewhat uncertain depression in it." Mr. Huggins observes that such a description coincides very well with existing aspects, and he does not think the absence of any notice by Schröter of a small interior crater is of much weight in indicating its subsequent formation. He adds, that "Lohrmann's description and that of Mädler do not appear to be in accordance with Schröter's observations, or with the present condition of the object."

WOLF ON LINNÉ.

(From "Comptes Rendus," June 17, 1867).

Since the 10th May I have noticed that the crater Linné continues to exist, but with a much smaller diameter than that of the crater indicated in the maps of Lohrmann or Beer and Mädler. In the centre of the white spot a circular black hole may be seen, bordered on the west by a portion of ground which seems prominent above the remainder of the spot. This slight extra elevation has already been described by Schmidt. Atmospheric circumstances did not allow me to obtain an irreproachable image of the moon before the 10th June. On that day, at 8 o'clock, Linné had already been in full light nearly 48 hours, and the central hole could be seen with perfect sharpness. It is a deep crater-deeper than most of the little craters surrounding it, if one may judge from the comparative intensity of the shadows; but its diameter is not equal to that of craters A and B of Beer and Mädler. The white spot which spreads radiatingly (s'étend en ragourant) round it, had, on the 12th June, a diameter of 4"5, that of Bessel being 7"-7. The crater itself subtending a little less than one second. The perfect purity of the atmosphere, and the optical power of the telescope (0m. 40) which I employed, allowed a number of small craters to be seen very distinctly round Linné, or rather a number of small round holes without elevated margins, and which are not shown in Beer and Madler's map. Six of these little craters form a very remarkable double range to the north and north-east of Linné. They are smaller than the craters in a line situate to the north-west of Linné, and noticed by Schmidt. I employed magnifications of 235, 380, and 620 times.

The brightness of Linné has not changed since Beer and Mädler's observations, for it is always equal to that of the white spot situated near Littrow, on the western margin of

the Sea of Serenity, to which B. and M. assigned the luminosity 6.

If, then, we compare, the actual appearance of Linné with the text of Lohrmann and his successors, it is possible, à la rigeur, to believe that it has undergone a certain change. Linné has always been a deep crater, with elevated margins; its lustre has not changed-its total diameter has remained about the same. A comparison of maps, on the contrary, indicates a real alteration, for these figure a large crater occupying all the space now filled by the white spot. Schmidt thinks that we cannot refuse to attribute great weight to the identity of the indications of these two maps. The authors of the second, having the first at their disposal, it is probable that if they had not found the great crater drawn by Lohrmann, they would have noticed so extraordinary a fact. It is not, however, without interest to compare their indications with that of earlier maps. The picture drawn and presented by Lahire, which is in the library of St. Geneviève, represents Bessel, Sulpicius Gallus, and other little craters, equal to Linné in the map of Mädler; but he does not indicate Linné. He has only many white spots in this part of the sea. Cassini's map appears merely a copy of Lahire with less detail. According to Schmidt's note, Schröter seems not to have seen Linné,* at least not as one of the principal craters in the Sea of Serenity, although he noticed others that were smaller.

If we consult the photographs of the moon, we see, in the large copy of Warren De la Rue (1858), Bessel and Sulpicius Gallus exhibiting an indication of an interior shadow, while Linné figures as a white spot. The same is seen, though clearer, in the enlarged copy of the magnificent photograph obtained by Mr. Rutherford on the 4th March, 1865.

The disappearance of the great crater of Linné, then, dates as far back as 1858, if not as far back as Lahire. Apart from the indications supplied by the maps of Lohrmann and Beer and Mädler, to which we may oppose the counter indications of Lahire and Schröter, we only possess a single positive document testifying that Linné has undergone any change, and that is the affirmation of Schmidt that his crater and drawings of 1841 represent the object differently to what is

now seen.

REMARKS OF ELIE DE BEAUMONT.

M. de Beaumont observed, when the paper was read to the French Academy, that if observers placed in the moon viewed Vesuvius or Etna before and after an eruption, they See Mr. Huggins's quotation from Schröter.

could only notice very slight changes. A great eruption even of Vesuvius would produce no other effect than to diminish slightly the depth of the semicircular trench of the Atrir del Cavallo, and to change its colour. Seen from the moon, such an alteration would appear problematical, and would give rise to discussions amongst observers. The observations made by P. Secchi on the 10th and 11th of February last ("Comptes Rendus," 25th February), tend materially to the belief that some change of this sort must have been produced in the configuration of the crater Linné, since the date of Lohrmann's and Beer and Mädler's maps. Moreover, it is to be desired that observations relating to the absolute permanence, or to very slight alterations on the moon's surface, should be multiplied, for a single change, however slight, would suffice to show that a geological life exists in the interior of the moon, as well as in the interior of the earth.

CURIOSITIES OF SOUND.*

PROFESSOR TYNDALL'S lectures on sound are, in their way, as admirable as the lectures on heat, which formed the foundation of his well-known work, "Heat as a Mode of Motion," though in dealing with the aerial vibrations which act upon our auditory nerves he has chiefly had to expound the discoveries of others, while in discussing the phenomena of heat it was his happy task to record many brilliant discoveries of his own. We are very glad that he has used plain English on his titlepage; a book on "Sound" promises to be intelligible and interesting, while a treatise on acoustics would look alarming and dry. All through the work before us we meet with indications of the learned professor's remarkable aptitude for presenting his subject in a simple and elegant form, and it is gratifying to be assured that the present book will do far more than has been accomplished by any preceding publication to popularize a branch of science that has suffered much neglect, from the erroneous impression that it was too abstruse for ordinary minds.

A world without sound would seem a dismal solitude to those who are familiar with human voices, the notes of birds, the cries of animals, the hum of insects, and the multitudinous noises of active life. What we call the silence of night and of waste places, and which, for a brief period, yields the

* "Sound :" a Course of Eight Lectures, delivered at the Royal Institution of Great Britain, by John Tyndall, LL.D., F.R.S., Professor of Natural Philosophy in the Royal Institution, and in the Royal School of Mines. Longmans.

sensation of calmness and repose, is not as soundless as we imagine; but even that would be oppressive if endured for long; and could we visit a planet without an atmosphere such as our moon is supposed to be, how appalling would be the dreariness of its great mountain shadows, throwing their huge black pall over the scene, as the sun deserted vast regions of crags and plains, in which not the faintest whisper of any voice was heard.

We have in several previous papers explained the nature of waves, and their propagation. Sound is the result of vibrations, or wave-movements, transmitted by the air to the delicate apparatus of our ears, and then reaching our brains, where they become transformed into sensations, of which the mind takes note. In wave-motion the particles of matter first affected vibrate or oscillate through small spaces, but they communicate their own motion to other particles; and so the wave-form spreads and spreads, until it becomes too feeble to be discerned. A stone thrown in a pond illustrates these actions. Circle after circle of ripples are formed, wider and wider, but shallower and shallower, until they are stopped by the banks; or, if the pond be big enough, until, in acquiring great width, they have lost so much depth, that they can no longer be seen. Further illustration of wave-propagation, as a series of spherical shells, will be found in the paper referred to; and though the subject may appear a little difficult at first sight, it will prove very simple when approached step by step.*

If we have an instrument capable of communicating strong vibrations to the air, such as a bell, and place it under the receiver of an air-pump, and strike it while in that position, we shall have a full sound while the receiver contains its ordinary quantity of air; but keep the bell ringing, and at the same time pump the air out, the bell sounds will grow weaker and weaker, until at last, if we make the vacuum sufficiently complete, they will no longer be heard at all. The intensity of a sound in a given medium depends on the force with which its particles are moved, or on the velocity of their motion. "Fix your attention," says Professor Tyndall," upon a particle of air as a sound-wave passes over it; it is urged from its position of rest towards a neighbouring particle, first with an accelerated motion, and then with a retarded one. The force which first urges it is opposed by the elastic force of the air, which finally stops the particle, and causes it to recoil. At a certain point of its excursion, the velocity of the particle is at its maximum. The intensity of the sound is proportioned to the square of this maximum velocity."

The intensity of a sound is, as we have seen from the air* See "Radiant Forces," INTELLECTUAL OBSERVEE, March, 1867.