sequence more characteristic, more "stringy." Schulze has extended his method to large pedal pipes, producing a stop of remarkable beauty, called the "Violone."

Applying the air-reed theory to this Schulze's "Gamba," we shall see how fruitful it is in illustration of the actual process of tone-making. Without diagrams and with but few technical terms it may be made clear and comprehensible. Let us take a specimen-pipe. It is of slender, graceful proportions, what is called "narrow scale," length thirty-seven inches and a quarter, diameter one inch and five-eighths, mouth or embouchure in breadth one inch and a quarter, and three-eighths of an inch high, and its pitch answers to the note E in the tenor octave. It has a very fine wind-way, large foothole, and is considerably overblown, for it will bear it. There is a bar in front of the mouth, fixed upon the little upright strips projecting at the sides about a quarter of an inch, which are termed ears; they are common to pipes until the size is too small to require it. Builders say the ears are added to pipes to steady the tone. On the theory advanced in these papers, we find their purpose is to prevent any flank move. ment of the atmosphere during the vibration of our air-reed, for the angle formed by the vertical line of the mouth and the line of force of the outwardly inclined stream of air presents an opening of weakness, and these ears are as ridges or outworks thrown up to guard against any premature invasion by the external air which, as intimated in an earlier letter, pierces through at the proper time only, just under the edge of the upper lip.

We readily perceive that the "Gamba" pipe has three specialties: overblown wind, to give a stiffer reed; a low-cut mouth, as a provision for shortness of reed; and wind much thrown out as a means compulsory for ensuring a greater amplitude in the reed's motion,—the result of the combination being that the tone is rich in harmonics; harmonics precede the groundtone, and follow it, and coalesce into it, and linger behind as though the last to quit the pipe. There is nothing more beautiful in all the varied wealth of an organ than a well-voiced "Gamba." Every tone suggests a symphony, many-tinted, autumnal. There is another remarkable feature peculiar to these the artist can shade them with less depth of ground-tone and more varied and delicate hues in the harmonics, which nevertheless come out more brightly in the contrast, and compensate the ear with a new variety, toned with less body yet with equal fulness, through the heightening of the harmonic colour, and the more gradual blending of the whole.

In the pipe we are examining we shall find that the wind is not so much thrown out as in the older class of the species, and herein lies the real meaning of the difference, for by the agency of the bar an equal amplitude is enforced in the air-reed, but one of new form: and see how gracefully it is drawn,-yes, happily we can see, for the new form bears an impress highly significant. A little bit of paper deftly applied will enable us to watch the process of nature. Take away the bar, and the pipe will not sound its ground-tone-it is only able to produce its string of brilliant harmonics. Look at the air-reed: how minute a space it traverses whilst these high notes are thrilling in your ears. In substitute for the removed bar, now lay a small pencil across the mouth, and see how in coy consent the air-reed yields, comes out to you with a fine curve, and all the power of the pipe is affirmed coincidently with this visibly extended amplitude of the reed's motion. You can change it from one state to the other by this movable bar, and you have to notice that the reed is almost upright in stem, but bends over, arching at the tip,notice also that the inward curve of the reed is less than the outward curve. The explanation of this influence will be quickly divined if you fully comprehend the way in which the reed builds itself up in a curve, leaning outward upon the external air: the air composing the rced issues from the wind-way in a dense stream; the particles are most compressed at the root, and gradually expand and become less energetic as they reach higher freedom -the velocity of the upward stream motion attracts the external air with force, strongly, to the root, bearing with lessened force on the less compressed portions higher up, and the gradation of force so mani ested gives rise to the curve-the curve delineates the force, we may say the curve expresses the constant flow of the surrounding air to this diversified region of "least pressure," its impulses being in graduated power from root to tip. By the bar we interfere with the direction of this flow, concentrate it more on the lower portion of the stem, and shield the tip of the reed from its influence; the upper portion, having thus lost so much of its natural support, is bent by the outflowing nodal wave of the pipe in a more supple curve, and to an extent

equal to the required amplitude for its pitch. The form differs now. The curve of the "Gamba" is not the same as the curve of the "diapason.”

The distinct agency of the air-reed and the nature of the aircolumn in relation therewith being evident, the inference follows that the note produced is dual, consists of two unisonous notes blended into one sound. Quite unexpectedly the chosen pipe furnished me with the talisman to prove its truth. When the reed and the pipe are suitably mated, the union is one of perfect harmony; but the reed rules always: it may be sharp to the pipe, but the pipe can never be sharp to the reed, for on the first intimation of such the reed is roused, and starts forth to a tone of higher velocity. How slight a matter may derange the union of the reed and pipe. If we tease the pipe with this pencil, peace is disturbed. Our beautiful little "Gamba" is very sensitive and high-spirited, and cannot help letting us hear a little of the inner life of the home when things go a trifle wrong. There is one particular place across the mouth for the fixture of the bar: if, resting the pencil at the upper points of the projecting ears, you leisurely bring it down, you will hear the changing harmonics; then, halting just a hair's breadth or so before the true position is arrived at, all tone will be lost, and there will suddenly break forth a wailing "who-hoo, who-hoo;" that torture will continue until you relieve the suspense by moving the pencil another shade in descent, when the discord will resolve into the perfect tone, instantaneously, as two dew-drops when they touch melt into one. Precisely the same "who-hoo" as we hear when tuning two separate diapason pipes so nearly in tune that they are only a shade out of unison and just on the point of accord. The "Gamba" pipe and the reed were similarly at variance; the air-reed, not having quite yielded to the outward influence of the bar, was a trifle sharp to the pipe; the supernodal wave was too short and unable to effect a synchronisation with precision, and therefore the phenomenon of beats was manifested. We could have lengthened the supernodal wave and flattened the note by adding a portion to the top of the pipe, when concord would have followed, as it did by lowering the bar, for in tuning it matters not which note of two is altered to bring about unison; we might alter either pitch of pipe or pitch of reed; but by the lowering of the bar we flatten the reed, and cause thereby the descent of the node (then an uneasy fulcrum) and the lengthening relatively of the supernodal column. As a listener remarked "there was surely a fight going on inside," we settled it by favouritism, taking sides with the little "Gamba," and gaining the reed over in concession of its strength for the sake of concord. That is the explanation as it suggests itself to me, practically, exhibiting how a strong reed drives the node higher up in the pipe, and a weak reed favours the opposite; thus determining the variations in the lengths of pipes of unisonous pitch, so long an unsolved problem.

Another point of some importance is also illustrated-that the earliest harmonics in the theoretical series may be out of tune with the fundamental. Here the introductory or transitive harmonics are, it is evident, all sharp to the ground tone, since the influence of the bar does not come into effect until its flattening power ushers in the fundamental; phenomena of this kind occur in other instruments mostly unacknowledged-it is admitted to be the case in the trumpet, which has No. 5 in the series flat, 7 still flatter, and 9 sharp. A diapason pipe will, however, exhibit the same in the small pipes of the higher octave; they may be blown to imitate exactly the clash of the trumpet.

As showing the essential nature of the curve of the reed under the influence of the bar, it is worth notice that in the earlier "Violone" stops thus treated a square-faced bar was fitted, but with not so good effect as when the rounded bar was adopted; and in the light of our explanation we see why it should be so, for the curve could not form itself truly. The best form of bar is that given by a split pencil, the half-round, with the flat surface outward. Many other points of interest will be deat with in another letter, on the interior movements of vibrating aircolumns.

The study of the organ-pipe in every mood of its behaviour will make untenable the elegant fancy of a promiscuous assemblage of pulses fluttering and clamouring at the lip of the pipe, one of which out of a thousand it selects. It is a fair-seeming explanation, and under the commanding name of Prof. Tyndail generally accepted, for nothing better had been devised in philo sophy. Not too strictly interpreting an ideality of expression, there yet remains an implied theory which is rot in any sense borne out by the teachings of experience. The artist has some prescience of the powers that are to work his will; in practice

there is nothing adventitious; the pipe is a mechanism designed to a precise end which it fulfils; it speaks but as it must; there is no selective power, for the hand that fashions it, ordains. HERMANN SMITH

Periodicity of Rainfall

IN his second letter (NATURE, vol. x. p. 263) Governor Rawson makes the following remarks:-"Mr. Meldrum, in his letter (vol. viii. p. 547), writes, that I have taken 1846 and 1871 as middle maxima years [in my first paper I also took 1848], whereas 1849 and 1872 are probably more correct. Mr. Meldrum is in error as to my having taken 1846 as a middle maximum, as a reference to my former letter will show. . . . I demur to the changes to 1849 and 1872: to the first because, without any sufficient reason, a dry year (48'10 in.) is discarded, and a wet year (67 88 in.) is added; and to the second, not because it affects my calculations, but because no reason is given."

In reply, I beg to observe that 1846 is either a misprint for 1848, or that in my manuscript 6 was inadvertently written for 8. This, I submit, is evident from the words immediately following the mistake, namely, "in my first letter, I also took 1848."

If Mr. Rawson supposes, or if his remarks imply, that I made 1849 a middle maximum, to avoid the small rainfall of Barbados in 1847 (48 10 in.) and at the same time to take advantage of the large fall in 1850 (67·88 in.), in order to make out a favourable case, I beg to say that he is entirely mistaken; for long before I saw his rainfall returns, I had invariably taken 1849 as a middle maximum year. The only instance in which I took 1848 was, as I said, "in my first paper" read before the Meteorological Society of Mauritius on Oct. 10, 1872. In all subsequent papers on the subject, including one read before the Royal Society, 1849 was taken. Righty or wrongly, therefore, the Barbados rainfall has been subjected to exactly the same treatment as that of the British Islands, the Continent of Europe, India, America, &c.

Assuming a causal connection between sun-spots and rainfall, it seemed to me that the effects, if any, would be most apparent about the times of the turning points of the sun-spot curve, and that a comparison of the rainfall of each maximum period of three years with that of each minimum period of three years, for a considerable time and space, would be a preliminary test of the hypothesis. The difficulty was to know the exact epochs of maximum and minimum sun-spot frequency, and at the same time the rainfall for equal periods on either side of them. If we had the monthly rainfalls, and knew in what month the maximum and minimum of sun-spots occurred, it would be comparatively easy to compare the rainfalls for equal times with respect to the epochs. But there was another point to be considered, namely, that a cause requires time to produce its effect.

According to Prof. Wolf 1848.6 was a maximum epoch; which, I presume, means that the turning-point occurred in August 1848; the figures, however, might mean six-tenths of a year after 1848, or August 1849.

1871, with a copy of which he has favoured me, I would remark that he has made apparently some oversights in his letter. For example, he says, with reference to a comparison of the rainfalls at Fairfield and Halton, "but the rainfall at Fairfield during the last three years. is 13'33 per cent. below that of Haltor. Therefore 21.7 in. have to be added to the minimum average of 1843-45, which would increase the above excess of 10'6 in." But if the minimum average be increased by a percentage, would it not be well to increase also the maximum average of 1847-49 by the same percentage? If this be done, the excess is not altered in the least.

The earliest rainfall observations at Barbados, given by Mr. Rawson, were those taken at Fairfield from 1843 to 1850, after which there is a long blank. Now, the rainfall there during that period gives the following results :Rain.

Min. years.

1843-45 163'7

Max. years.
Rain.
1848-50........ 179.7

showing an excess of 16 inches in the maximum period.

The next earliest and most complete observations are those taken at Husbands; they commence with 1847, and have been continued without interruption. From them we get :

maximum sun-spot.

I do not think that these results are opposed to the hypothesis which Mr. Lockyer and myself have put forward. As a matter of fact, the rainfall of Barbados, as given by Mr. Rawson from 1843 to 1868, bears out the hypothesis if we take 1849 as a middle maximum in place of 1848; and it is for others to judge whether the reasons that have been assigned for the change from 1848 to 1849 (not for Barbados alone, but generally) are valid. But it may be said that the rainfall of 1871-73 was opposed to the hypothesis. I have not the rainfall for those years before me. Granting, however, that they show a very considerable diminution, the question arises whether the favourable result of twenty-six years (1843-68) are to be upset by the unfavourable results of three years (1871-73)? Have we not in meteorology many such exceptions to well-established laws?

The rainfall at 250 stations in different parts of the world has now been examined, and the results are so decidedly favourable Barbados is for or against the theory. I think the more the subthat it is practically of no consequence whether the experience of ject is examined, the more clearly will the law come out ; but we must be guided by facts, and not hesitate to discard this or any other theory when unsupported by facts. Mauritius, Oct. 15 C. MELDRUM

Ice-Caves

THE occurrence of snow and ice in an old mine during the month of June, mentioned by Mr. J. Clifton Ward in his in

Taking August 1848 for the maximum epoch, the strict course, in order to place the epoch at the middle of thirty-six months, would be to give the rainfall from the 6th of February 1847, to the 6th of February, 1850. But this could not be done. It was necessary to choose a whole year as the middle maximum year. And the reason why 1849 was chosen in preference to 1848 was, that the object being to find whether the periodic changes indi-teresting paper in NATURE, vol. xi. p. 309-to the accuracy of cated by sun-spots had any effect upon rainfall, and time being required for a cause to produce its full effect, there was a presumption that the maximum rainfall would take place after the maximum of sun-spots, somewhat in the way in which the maximum diurnal temperature occurs, not at noon, but an hour or two after noon.

For a similar reason 1872 was taken as a middle maximum in preference to 1871.

This allowance of time for the supposed cause to produce its effect is, though apparently unintentionally, made by Mr. Kawson himself when he adopts 1844, 1856, 1860, and 1867 as middle years; for, according to Wolf, the epochs were 1844 0, 1856-2, 1860'2, and 18671, that is, if I mistake not, early in each year; so that nearly two of each of the three years taken come after the epoch, while only one of them precedes it. By taking 1849, therefore, as a middle maximum year, we come nearer to the conditions observed with respect to the other epochs than we should do by taking 1848.

Before proceeding to deduce a few results from Mr. Rawson's valuable Report upon the Rainfall of Barbados," from 1843 to

the greater part of which I can bear personal testimony-has a more exact parallel in the Alps than "a Swiss glacier," namely, a glacière. These remarkable caverns have been fully describer by Mr. G. F. Browne in his able and pleasant work, "IceCaves of Switzerland and France;" and briefly by myself in "The Alpine Regions." Since the publication of that book I have seen others; and as one of these has never, I think, been described in any English work, I venture to take the opportunity of sending you a short account of it. It is in the Val d'Hérens, a short distance from Evolena, on the way to the Pic d'Arzinol, and is called the Pertuis Freiss. A slip or subsidence of part of a cliff appears to have cracked the rock and opened two joints, into one of which fissures one can descend. This is about four feet wide and generally some four yards high, the floor being a little below the level of the ground outside. The crevice comes to an end in about a dozen yards. Against the slightly sloping wall of rock rested some pendent sheets of ice, whose thickness rarely appeared to exceed three inches, and irregular patches of ice lay about the floor. The temperature of the air appeared to be a little above the freezing (unfortunately, I had

afforded by 36 Ophiuchi and 30 Scorpii, which was first pointed out by Bessel in the "Fundamenta Astronomiæ." If we compare Lacaille's positions (taking them from the reduced catalogue published by the British Association) with those given by the late Capt. Jacob from the Madras observations 1853-57, we find with the Pulkova preces

sions

not a thermometer with me). It was a warm summer's dayJuly 23. The ice exhibited the usual prismatic structure, but the prisms seldom exceeded a third of an inch in diameter. I was informed that in winter it was choked up with snow. The other fissure also contained ice, but as it was less accessible, and seemed in no way different from the former, I did not enter it. The especial interest of this case is that it affords what I might call the most rudimentary type of a glacière; a natural icehouse, replenished every winter, and perhaps sometimes entirely cleared out during an unusually hot summer. The "Grotto " on Monte Tofana, near the Ampezzo Pass (which I have not + 237"'5 -749 been able to visit), is, I expect, another of this kind. +238" 7 - 79'6 St. John's College, Cambridge T. G. BONNEY The introduction of Brisbane's places would only [By a misprint "glacier" was put for glacière in the last para- modify the above figures in a trifling degree. graph of Mr. Ward's paper.-ED.]

A few of the letters, e.g. J (the word for which might be regarded as a new way of spelling Ujiji), O, and Q, present a little difficulty, which some of your readers may lessen. As it is, these exceptional cases are so quickly impressed on the memory that the code thus learnt can be written in a surprisingly short time, and read soon afterwards. It is hardly possible the plan here suggested can be new, yet, as I have not met with anything similar, I venture to send it to you for publication.

W. F. BARRÉTT

The Micrographic Dictionary-Pollen Grains AT present I have to do with the "Micrographic Dictionary" and the two other works mentioned in my letter printed in NATURE, vol. xi., p. 286. If the pollen grains of Mimulus moschatus are variable (as now stated by Mr. Cooke on the authority of Dr. Mohl), how is it that the figures and descriptions in the books mentioned are all alike? There is no variability here, but wonderful sameness both in illustrations and letter-press.

As the accuracy of my first simple observation has been called in question, I will add another. In the "Micrographic Dictionary," Pl. 32, Fig. 28, is given the pollen of Sonchus palustris. This, like that of the Mimulus, is totally wrong, the reticulation is by no means correct, and the abundant spines with which this pollen grain is clad (so common in the Compositæ) are totally omitted. Now, on turning to the Rev. J. G. Wood's book, Pl. 3, Fig. 24, this erroneous figure is reproduced with incorrect reticulation and no spines, and on referring to Mr. Cooke's work, Pl. 2, Fig. 6, the same errors are again perpetrated. W. G. SMITH

OUR ASTRONOMICAL COLUMN AND RETICULI.-These stars of about the sixth magnitude appear to offer a similar instance of large and nearly equable proper motion to the well-known one

...

R. A.

Secular Proper Motion.
N.P.D. Arc of great

circle.

130"3

133"-8

Direction of motion.

54°9 534

When competent observers in the southern hemisphere are provided with heliometers for research on stellar aarallax, there will be no lack of objects to occupy their pttention, and we may expect most important results from such investigations.

η

be able to make a fair approximation to the orbit of this THE BINARY STAR 7 CASSIOPEÆ.-We may very soon double star, and so, with Mr. Otto Struve's value for the annual parallax, form some idea of the real dimensions and mass of the system, as is already the case with a Centauri and 70 Ophiuchi. An orbit given by Mr. Powell, of Madras, in vol. xxi. of Monthly Notices, R. A. S., is probably vitiated by typographical error or errors. Struve's parallax is o"154 0045.

THE BINARY STAR a CENTAURI.-According to Mr. Powell's last elements, which are founded on measures up to 1870 inclusive, the components, at the present time, are nearly at their minimum apparent distance (12), and the angle of position is advancing at the rate of 10" monthly. It may be hoped this fine object is receiving due attention from astronomers in the southern hemisphere at this critical period of the revolution. There would appear to be no probability of such difficulties attending observations at the passage of the peri-astron as those presented by y Virginis in 1836, so far at least as can be judged from the measures to 1870.

RED STARS.-Amongst the red stars notified by the late M. Chacornac, is one which he estimated between the seventh and eighth magnitude, and of which he says, "éclat terne et nebuleuse." The position assigned identifies the star with No. 1172 of Rümker's Catalogue, whence for the commencement of the present year its right ascension is 4h. 16m. 16s., and polar distance 67° 19'7. Rümker calls it a sixth magnitude, and Argelander (Durchmusterung) an eighth. Although different eyes will not always agree in estimations of brightness of the ruddy stars, there appears here to be a suspicion of variable light. Another of Chacornac's isolated red stars he himself indicates as variable. called 6 mag. by Lalande (No. 41453), 5'6 by Argelander, It is Oeltzen 21356, 5 in the Washington Zone, 1848, July 24; while Chacornac remarks, "sometimes brighter and sometimes fainter than a star of the seventh magnitude near it," which is probably Oeltzen 21386. Position for 1875, R.A. 21h. 17m. 5s.; P.D., 111° 22'7. Neither of these stars is in Schjellerup's Catalogue, but that list is very far from being a complete one.

ENCKE'S COMET.-The extreme faintness of this comet at the present appearance is attracting the attention of astronomers who have had most experience of the circumstances of previous returns. Last week we quoted the remark of M. Stéphan on this subject, and we learn from him that he was using a newly polished mirror in the great Foucault telescope of the Observatory of Marseilles. In 1868 and 1871 the comet's appearance was very similar to what it had been in previous years under analogous conditions. In discussing the probability of any real change in the comet's constitution, it may, however, be well to bear in mind that in the year 1842, when the peri