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one hand, and with carbon and hydrogen on the other, as that ground to the impossibility of any considerable porin the explosives, e.g. nitroglycerine.

tion of the lithosphere being fluid, because the earth does Living substance has apparently all the above mentioned not undergo the deformation which the physicist would sources of instability, and perhaps not the least important expect owing to the tidal action which should be set up is that it has for its pivot nitrogen, the element which within it, might possibly be seen in a fresh light on taking above all others is remarkable for the lability of its com- | into account the remarkable facts demonstrated by Prof. pounds. I have elsewhere indicated the probability that John Perry in his lecture on spinning tops, which he gave the active molecule of living substance consists of an to an audience of working men on the occasion of the enormous complex of proteids, carbohydrates, &c., linked meeting of the British Association at Leeds in 1890. As together by means of the nitrogen atoms, and that the a “working inan" in a real sense of the word, I conoxygen store is more or less combined with the nitrogen. sidered myself privileged to attend that lecture, and was At the death of the molecule its constituent groups (pro rewarded by finding in my own mind a great difficulty teids, &c.) are released, and the store of oxygen passes cleared up by Prof. Perry's masterly demonstrations of the from the nitrogen into other and more stable forms of practically rigid condition of non-rigid bodies, if only made combination.

F. J. ALLEN. to rotate with sufficient rapidity, as the equatorial regions Cambridge.

of the earth do-something like 1000 miles an hour. Bishop's Stortford, April 17.

A. IRVING. Chalk Masses in the Cliffs near Cromer.

Rival Parents. At the present time the cliffs near Cromer exhibit some

A CURIOUS example of the rival claims of a pair of interesting chalk masses in the Glacial drifts. Between

thrushes and a pair of blackbirds for the parentage of a East and West Runton Gaps are several of great size and

young blackbird is being observed in my garden. remarkable in position. One, a very long slab-like mass,

A pair of blackbirds built a nest in a small thick laurel, is bent from being nearly horizontal until it is almost

and in another shrub, some 4 feet off, a pair of thrushes vertical, and thus comes to within a short distance of

also built a nest. The young in both nests were hatched the top of the cliff. The masses near Trimingham will

out at the same time, and were successfully reared until now repay a close study, for they have changed greatly

they were some eight or nine days old, when a cat attacked during the last five years. Both my friend, the Rev. E.

the nests (Monday, April 17), killing all the young thrushes Hill, and I have made notes and rough sketches, with the

and all the blackbirds except one, which was found hidden intention of sending to the Geological Magazine a short

under the shrubs. It was continually visited after the account of what can now be seen ; but we earnestly hope that some geologists who are adepts at photography will

tragedy by both the old thrushes and old blackbirds, and

two or three hours later was removed in some way not visit both localities at the earliest possible opportunity, in

observed to a shrubbery twenty or thirty yards away. order to secure a permanent and accurate record of these

There for the last five days it has been fed and looked exceptionally interesting sections.

T. G. BONNEY.

after by both pairs of birds, who mob with exceptional

vigour any intruding cat or dog. The young bird seems The Rigidity of the Earth's Interior.

to have thriven mightily under the attentions of its true The letter of Dr. T. J. J. See (NATURE, April 13, p. 559)

and foster parents, who appear in no way to be jealous deals with a subject of profound interest to students of

of one another.

KENNEDY J. P. ORTON. the larger problems connected with physical geology. But

University College of North Wales, Bangor, April 21. it appears that, in Dr. See's treatment of the subject, he has overlooked an important point, which I dealt with in

The Measurement of Mass. a paper read before Section C of the British Association

In the notice of my little book, “ Radium Explained," at Birmingham in 1886. Therein I directed attention to

un April 6, twenty-nine lines are devoted to showing that the fact that “gravitation " is only a special instance of

I have reached a wrong conclusion through not knowing the law of universal attraction, and as a corollary to

that mass is measured by inertia, and I am corrected in this, at any considerable depth within the sphere of the

these words :--" how is the quantity of matter to be ascerearth, an appreciable factor of what I may call negative

tained? The choice practically lies between defining mass gravity must be allowed for, owing to the counter

by inertia at a given speed or by gravity. . . . As, however, attraction of the mass of matter situated nearer the surface

gravity depends on local circumstances, while inertia (at of the sphere ; so that a body placed at the centre of gravity

given velocity) does not, the latter property is preferred of the earth, whatever its mass or density, would have no

for the definition of mass, as being more fundamental.” weight at all.

So far from rejecting this principle, I state it, in almost I am glad to see that the consideration of “critical the same terms, on p. 84 of my book :-" Mass, or temperatures" of quasi-solids (the importance of which

quantity of matter, is usually ascertained by weighing. was emphasised in my little work on metamorphism

But weight is merely the force with which the earth some fifteen years ago) is receiving serious attention, and

and attracts, and this varies with our position on its surface. I may also point out that the idea of a potentially liquid

To get an absolute test of mass, which would be in(or even gaseous) condition of a mass at depths in a

dependent of position, we may measure the force required practically rigid state is not new; it was treated in a

to move or stop a body at a certain speed." And nowhere masterly way by Prof. Albert Heim, of Zürich, some

in the book have I supported any argument by the retwenty years ago, in his magnificent work“ Ueber den

pudiation of the principle here clearly stated. This is a Mechanismus der Gebirgsbildung.” “Ueberlastet " is the

question of fact; the other objection taken is equally illword used by Heim to express such conditions, where the

founded, but, being on a controversial point, it cannot be pressure is so far “hydrostatic" as to consist of com

dealt with so briefly.

W. Hampson. pression acting equally (for the time being) in all direc

West Ealing, May 1. tions. Any disturbance in a given portion of the lithosphere of the equilibrium thus existing must result in

Properties of Rotating Bodies. shearing movement if the disturbance be small, and in flow PROF. W. H. PICKERING, in NATURE of April 27 (p. 608). in a given direction if the relief in that direction from refers to the property which a rotating body possesses of pressure is great and rapid enough. In the former case assimilating, in certain circumstances, its axis of rotation we should get “metataxic change," in the latter to a secondary axis of rotation or revolution impressed schistosity; for I still challenge the statement, made upon it, and he mentions the fact that this property is recently by a high authority, that “it is only a question rarely described. of degree between the cleavage of a slate and the foliation It was fully discussed in an elementary lecture given by of a crystalline schist or gneiss."

Prof. Perry at the Royal Institution about fifteen years Questions relating to tidal action in the rotating litho- | ago, and afterwards published in the Romance of Science sphere, and even Lord Kelvin's oft-repeated objection on Series under the title " Spinning Tops." 1 Report Brit. Assoc., 1896, p. 983 ; and Pror. Birmingham Nat. Hist.

E. W. ROWNTREE, and Philos. Soc., 1899.

20 Queen Square. W.C., May 1.

RECENT SPECTROHELIOGRAPH RESULTS. which the solar image is moved across the primary

slit by means of the declination motor which moves IN a previous number of this Journal (vol. lxix. at the same time and rate the photographic plate; 1 p. 609, 1904), under the heading of “ A New or the primary slit, and with it the whole spectroEpoch in Solar Physics," I gave an account of the heliograph, may be moved across the image formed magnificent work that Prof. Hale had recently been at the focus of the equatorial. The first method is accomplishing at the Yerkes Observatory with his that adopted at the Yerkes Observatory, and the latest form of spectroheliograph, the instrument being second that at' Potsdam. worked in conjunction with the great 42-inch Yerkes. There is a further method in which a stationary refractor, which forms an image of the sun seven solar image is formed by means of a siderostat and inches in diameter.

lens, and the spectroheliograph is mounted horiIn the present article it is proposed to give a brief zontally and moved in an east and west direction description of another instrument based on the same across this fixed image. Such a mode of procedure principle, an account of which was published by M. is that employed at South Kensington. Janssen, and to indicate some of the results which The advantage of the last mentioned arrangement have been obtained with it. This instrument has is that there is no limit to the size or weight of the been at work at the Solar Physics Observatory during spectroheliograph; the uniform motion required can the past rear, and in a recent communication to the be easily and efficiently secured, and lastly, this

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FIG L-The spectrobeliograpas, showing the general arrangement of the two slits, the collimating and camera tubes, the moving (upfer) and fized

(lower) triangular frameworks.

Royal Astronomical Society I gave a more full motion does not in any way affect the steadiness of account of it, to which reference can be made for more the solar image under examination. detailed information than is here given.

The South Kensington instrument was erected in it is not necessary in this place to refer at any length the year 1903, but it was not until last year that satisto the principle which underlies the construction of a factory photographs were secured and routine work spectroheliograph, since this was referred to in the begun. This success was due to the use of a larger article above mentioned. It will suffice here to say, lens (12-inch) for throwing the solar image on the therefore, that the pictures produced by this new primary slit, the previous lens of 6 inches aperture method of solar research give us photographs of the not giving a sufficiently bright image. sun in monochromatic light, or in rays of any par. In this curtailed description of the instrument referticular wave-length that is desired. Thus if we re-ence of any length need only be made to the spectroquire to study the distribution of hydrogen on or heliograph proper. There is nothing particularly around the solar disc we employ a line in the spectrum novel about the siderostat, except, perhaps, its more of hydrogen, if calcium a calcium line, or iron an than usual size, the large mirror of 18 inches iron line.

diameter, the two small motors for operating the slow There are, however, several methods of using the motions in right ascension and declination, and a spectroheliograph. This instrument may either be modified form of Russell control for regulating employed in conjunction with a large equatorial, in the speed of the driving clock. This instrument is placed in a separate house the upper portion of which slit (Fig. 2) the solar image can be analysed in this can be rolled back towards the north. Some distance wave-length. due south of this, in another building, is the 12-inch For photographing the whole disc of the sun or Taylor photo-visual lens mounted on a concrete pillar, | its immediate surroundings with one exposure the and still further south, and in the same building, is lengths of the slits must be greater than the diameter the spectroheliograph, also mounted on concrete of the solar image (2 inches); in the present case they pillars.

are 3 inches long. Further, owing to the fact that Wtih this arrangement the solar beam is thrown the lines in the spectrum are curved, the secondary by the siderostat mirror continuously due south and slit jaws are curved to the same radius ; this necessi. in a horizontal direction; this beam then falls on the tates very accurate adjustment of the secondary slit 12-inch lens, and the solar image in the focus of this on the line, and means are provided to facilitate such lens is thrown on the primary slit plate of the spectro- requirements. heliograph.

In order to obtain a photographic record of the sun In order to analyse the solar image by allowing in monochromatic light, a fixed photographic plate is each portion of it to fall successively on the primary held by means of a wooden support as close to the slit, the latter, and consequently the whole of the secondary slit as possible (Fig. 2). In this way, as spectroheliograph, has to be moved horizontally in an the primary slit moves over the stationary solar image, east and west direction, a distance a little more than so the secondary slit traverses with equal speed the the diameter of the solar image (in this case stationary photographic plate. 2 inches). Further, this motion has to be extremely Up till now the secondary slit has usually been uniform.

The method adopted to accomplish both of these requirements is as follows:-A triangular iron framework (Fig. 1) is supported on three levelling screws on three concrete pillars. A second framework of the same size and material is placed on the first, but separated by steel balls free to roll between small steel plates fixed to each framework near the corners.

The longer side of this isosceles triangle is placed in a north and south direction. The direction of motion of the upper framework is restricted to an east and west line by means of a guide bar fixed to the lower framework; two small levers with rollers attached to the upper framework are pressed against this guide bar by means of small weights, thus ensuring the correct direction.

The actual motion of the upper framework is obtained by weights attached to one end of a steel strap the other end of which, after passing over a pulley mounted on an arm on the lower framework, is fixed to the western corner of the upper framework. This weight always tends to pull the upper framework towards the west, that is towards the right in Fig. 1.

The motion is controlled by a plunger projecting downwards from the upper framework operating a piston in a cylinder full of oil attached to the lower framework. The outlet valve can be so adjusted that any desired rate of motion can be obtained.

Owing to changes of temperature of the oil, different rates of movement can be obtained for any one reading of the micrometer head regulating the

Fig. 2.-'l be primary slit is on the left and the secondary behind the plate

carrier is se-n on the right. This illustration shows also the metal disc outlet valve. It is necessary, therefore, when making in position for a "lumb" exposure. an exposure for a “disc ” or “limb " picture to take the temperature of the oil into account. This is adjusted on the “K” line of calcium by eye estimaccomplished by employing a table, made fromation aided by a small watchmaker's lens, a check previous “ runs," in which the valve setting can be being made by taking a photograph of the specdirectly read off from the temperature reading and the trum, if possible with a sun-spot region, on the required length of exposure.

primary slit. On bright days ihis setting can be It is on the upper framework that the optical parts made with little difficulty, but during the late autumn, of the spectroheliograph are placed. These consist with a low sun, the “K” region of the spectrum is of a double tube carrying the two slits (Fig. 2) at the not easy to see, and the setting is in consequence northern or siderostat end and the two lenses (4-inch) | very uncertain. A new method just brought into of equal focal length at the southern end. The dis operation entirely eliminates this difficulty, for at a persion is produced by a single prism of 60°, and a constant distance on the red side of the “K” line reflector is inserted in the system in order to make a small glass plate has been set with a cross engraved the total deviation of the beam 180°. Thus the part on its surface which can be adjusted on a known of the solar image which passes through the primary line in the more visible region of the spectrum. By slit falls on the collimating lens, is reflected by the bisecting a particular line with the cross the “K" 6-inch mirror on to the prism, traverses the latter, and line is adjusted on the slit jaw simultaneously. finally, after passing through the camera lens, is! The photographs taken during the past year have brought to a focus in the plane of the secondary slit been of two kinds, the first to investigate the disin the form of a spectrum. By isolating any par- | tribution and area of the calcium clouds, or flocculi ticular line in this spectrum by means of the secondary as Prof. Hale has termed them, on the sun's disc, and the second the distribution and forms of prominences / Without entering into too minute details, the followround the limb. To obtain the latter, a metal disc ing brief summary of the more salient facts derived just a little smaller than the solar image is placed from a general survey of the photographs taken close up to the primary slit plate (Fig. 2), and re- ; during the past year may be given. tained there by a metal wire fixed to a firm base; this! Dealing with the “ disc " pictures in the first indisc is so adjusted that it is concentric with the solar stance, all of them show a “mottling" of very image. While in use it becomes extremely hot, and definite character extending from the equator to the it is therefore necessary that it be made of metal and poles. Nearer the equatorial regions this mottling riveted to the wire which supports it. These limb seems to become exaggerated in size in patches, some pictures, an example of which is given in Fig. 3, are of the interspaces becoming filled up, giving rise to

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of a composite nature in that after the exposure of the prominent flocculi, many of which clearly indicate the limb has been made the metal disc is removed the mode of structure. Fig. 3 gives an idea of their from the primary slit, and a “disc " exposure is appearance in the photographs. It will be seen that made on the same plate. It has been found by ex- į there are frequently long streaky bright portions perience that a " limb " exposure requires about sixty springing apparently from a central nucleus and times the time that is necessary for a "disc" ex- , having subsidiary ramifications. A three-legged formposure. Under very favourable conditions fifteenation is a very common type of structure in many of seconds is necessary for the latter and fifteen minutes the photographs. for the former..

These flocculi, in the first instance, esist alone, but

of the limb are secured, an opportunity is afforded of studying the changes in the form of large prominences after intervals of a few hours. Two examples of such changes are here illustrated and briefly de

in some of them spots appear at a later stage. No spot has been photographed unaccompanied by a flocculus; in fact, the duration of a spot is only a brief interval in the life-history of a flocculus.

Another interesting subject of inquiry is the position of a spot in relation to the flocculus. Spots more generally make their appearance near the head of, or, in other words, precede the apparently trailing masses of the calcium clouds with respect to the solar rotation, which is from east to west. Some examples of these are given in Fig. 4. When there are two fairly large spots in one flocculus, the larger one nearly always precedes the smaller one.

The composite pictures (Fig. 3) showing the

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Fig. 5.-Showing changes in prominences after an interval of one hour.

(Lower picture taken last.)

April 27

July 14

scribed. In Fig. 5 we have two photographs (only the portions of the limb indicating the particular region of the sun in question are shown) which were taken on July 14, 1904, at uih. 8m, a.m. and 12h. Sm. p.m, respectively. It will be noticed that during this interval of about one hour a startling change has occurred to the largest prominence; not only has its height been considerably increased, but its form has entirely changed. The material radiating the calcium light seems to have been ejected from the chromosphere and then to have apparently met a strong current moving polewards (that is, from left to right in the figure) which has thrown this material in that particular direction. The change of height from about 50,000 miles to 60,000 miles in this interval corresponds to a velocity of nearly three miles a second.

Not less interesting is the apparent disappearance of the second large prominence in the figure situated on the left.

Another example of a change of form of an enor.

August 2

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August 29

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“limb” and “ disc " have also brought to light many interesting points which call for further inquiry. In the first place prominences both near the solar poles and equator give strong images in calcium light. Secondly, prominences, which occur nearer the solar poles than the flocculi, do not appear to disturb the regular mottling on the disc in these high latitudes.

Fig. 6.-Two views of a large prominence taken with a four hours' interval Again, an intense flocculus, when on the limb, is

between them. (Lower picture taken last.) not always accompanied by a large prominence. These two last mentioned facts seem to indicate that mous prominence photographed on July 19 at flocculi and prominences are not always interdepen- uh. 45m. a.m. and 3h. 591. p.m. respectively is that dent phenomena.

shown in Fig. 6. This prominence was situated in On continuous fine days, when several photographs | the south-east quadrant. The approximate dimensions

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