« PreviousContinue »
the best arranged of continental observatories. While in We learn from Science that Dr. George H. Horn, the eminent the position of Director, Winnecke's health finally broke entomologist, died at Philadelphia on November 25. He was down, and for a great many years he has been unable to
one of the Secretaries of the Philosophical Society, and was take any part in the management of the establishment he formerly Corresponding Secretary of the Academy of Natural had so admirably fitted and equipped. W. E. P.
Sciences. He had been until recently professor in the University of Pennsylvania, though his connection with that institu
tion was chiefly honorary. Dr. Horn was only fifty-eight years NOTES.
of age, and his death, following those of Cope and Allen, is a
further severe loss to the city of Philadelphia and to science in The Physico-Chemical Institute of the University of Leipzig,
America. of which Prof. W. Ostwald is director, will be formally opened by a ceremony to be held in the large lecture theatre of the
La Nature announces the death of Prof. A. Joly, director Institute on January 3.
of the chemical laboratory of the École normale Supérieure, and Dr. Hugh GALT, acting Professor of Forensic Medicine professor in the Paris Faculty of Sciences. Born at Fontenayand Public Health at Glasgow University, has for some time sous-Bois in 1846, M. Joly entered the Normal School in 1866. back been engaged in a research upon the starches, which is
When he left this school he became attached to Saint-Claire likely to prove of value to the Department of Public Health. Deville's laboratory, and afterwards was professor of physics at
the lycée Henri IV., which post he occupied until he was MR. JOHN MILNE writes that arrangements have been made for the establishment of horizontal pendulums, with photographic The titular director of the laboratory at that time was M. Debray.
nominated sub-director of the laboratory of the Normal School. apparatus to record unfelt movements, at Toronto, Harvard,
M. Joly next became instructor (maître de conférences) in Philadelphia, Victoria, B.C., New Zealand (two), Batavia
, chemistry at the Sorbonne, and then professor attached to the Madras, Calcutta, Bombay, Mauritius, the Cape, Argentina, San
Faculty of Sciences of Paris. His works refer principally to the Fernando, and Kew, whilst a number of other stations are under
rare metals (niobium among others) and acids of phosphorus. consideration. Seismograms have already been received from Toronto. At his station on the Isle of Wight, for purposes The first ordinary meeting of the Röntgen Society was held of comparison, Mr. Milne has also two horizontal pendulums on December 7, Dr. Gladstone, F.R.S., being in the chair. writing on smoked paper, and very shortly a Darwin bifilar Mr. A. A. Campbell Swinton read a paper on “Adjustable pendulum is to be established. To this will be added later a X-ray Tubes,” in which various methods were discussed for von Rebeur. Paschwitz apparatus, with which type of apparatus regulating the penetrative and other qualities of X-rays, and for Mr. Milne worked for many years in Japan.
compensating the unavoidable and troublesome variations in
vacuum that are found to occur in practice. The paper was Dr. Charrin has been appointed to succeed Prof. d'Arsonval
illustrated by numerous experiments, and several adjustable in the chair of Medicine of the Collège de France.
tubes of Mr. Swinton's design, embodying the improvements A NEW branch of the Russian Geographical Society has just and principles enunciated, were shown in operation. been opened at Tashkend, for Turkestan.
The ninth Congress of Archæological Societies was held at On December 4 the friends and pupils of Dr. C. Cramer, the Burlington House on December 1, the Right Hon. Viscount professor of botany at Zürich, celebrated the fortieth anni.
Dillon in the chair. The Hon. Secretary reported that the versary of his connection as teacher with the Polytechnic in Committee had authorised the completion of Mr. Gomme's that town.
Index of Papers from 1682, with a view to immediate Prof. Dr. Willi Ule has just taken over the editorship of publication. It was reported that a wish had been exthe weekly scientific periodical Die Natur, which was founded pressed to have an index of the archäological articles in certain by Dr. Otto Ule and Dr. Karl Müller, and is now in its forty- journals and publications, other than the Transactions of sixth year of publication.
Societies. The Standing Committee had considered the subject,
and recommended that if anything were done it should be by WE regret to see the announcement of the death of Mr. adding a supplement to the Index as now published. After Gardiner G. Ilubbard, President of the National Geographic discussion the question was referred to the Committee with power Society, Washington. The death is also announced of Dr.
to act, if they found they could do so to advantage and at Campbell Morfit, formerly professor of applied chemistry in the reasonable expense. It was resolved, on the motion of Sir John University of Maryland, and one of the scientific advisers of Evans, K.C.B.: “That a memorandum be sent to the various the United States Government.
local Archäological Societies, suggesting the desirability of At the close of a lecture delivered by Lieut. Peary in Edin. placing themselves in communication with the Ordnance Survey burgh on Friday last, under the auspices of the Royal Scottish officers for their districts so as to promote the record on the Geographical Society, Dr. J. N. Murray, on behalf of the surveys of the earthworks within their districts, and where posCouncil of the Society, presented him with the medal of the
sible to determine their age by excavations.” Mr. C. Hercules Society in recognition of his work in the Arctic regions.
Read, the Secretary of the Society of Antiquaries, made a
statement as to the steps that had been taken by Government in A BROOKLYN correspondent sends this item of news :
response to the request of the Society of Antiquaries for infor. * Prof. Langley and Prof. Elfreth Watkins have constructed
mation as to what is done in foreign countries for the protection a Aying machine designed to draw a railroad car. This has of ancient and historical monuments. Full information had been tested for several days on the Medford branch of the been obtained and would shortly be published in a Blue Book. Pennsylvania Railroad, near Mount Holly, N.J., and has drawn It appears that in no country in Europe is so little protection the car at the rate of six miles an hour. The machine is actuated given as in England. Mr. Hope read a draft report on the by a gasoline engine, the power being applied to two propellers, best mode of indexing the Transactions of Societies ; this had about four feet long, which make 800 revolutions per minute.
been prepared by the Committee consisting of himself and Mr. It is expected that machines be constructed on this principle, J. H. Round and Mr. Gomme. As it appeared that several which can draw cars at the usual railroad speed.”
Societies were anxiously waiting for the recommendations, it was
agreed that the report should be referred back to the Committee are these five contributions to human knowledge : the establishfor final consideration, and that as soon as complete it should be ment of the principles of evolution ; the establishment of the issued to the Societies. The Hon. Secretary reported that a principle of the conservation of energy; the development of National Photographic Record Association had been formed mathematical science and its application to physics, mechanics, under the presidency of Sir J. Benjamin Stone, M.P., who had electricity and astronomy; the development of spectrum analysis been at the head of the original Warwickshire Survey. He was and the consequent discoveries respecting light and electricity; directed to communicate to the Association that “The Congress and the discovery of the nature and functions of bacteria, and of hears with great satisfaction of the formation of a National Photo- their influence, for weal or woe, upon living organisms. graphic Record Society, and expresses its desire to assist the
As the result of an investigation of the red spectrum of work in any way it can.”
argon, Dr. J. R. Rydberg comes to the conclusion (Astro. MR. W. A. KNIGHT, writing from Bruton, Somerset, in- physical Journal, November) that it belongs to one single forms us that on November 30, at 10.20 p.m., he was fortunate element. Moreover, there seems to him to be no reason to enough to observe there a splendid lunar rainbow. The moon doubt that the blue spectrum belongs to the same element, but was sufficiently near the horizon to give a large are, and although corresponds to a higher temperature. As to the supposed disit was scarcely quarter-full, the black clouds looming in the placement of a great number of the lines of the white spectrum north-east made the bow appear quite bright. There appears to towards the red end of the spectrum, it is remarked, nothing be no doubt that what Mr. Knight saw was a lunar rainbow and seems to indicate that we have to do with a continuous disnot a halo, for it was opposite the moon.
placement, but rather with the appearance of new lines on the PROF. A. RIGGENBACH has sent us the results of seven
red side of those of the other spectra, with which they ought to years' rainfall observations at Basle, deduced from a self
be closely related. In such a case it seems most probable that
the interesting observation of Eder and Valenta depends on a recording gauge. Of course the period is very short, and in dealing with monthly and annual means the author combines change in the relative intensity of two sets of connected lines.” the values with those of an ordinary gauge, giving altogether a In the Philosophical Magazine for December, Mr. J. D. series of thirty-three years. But the principal object of the Hamilton Dickson examines the relation between the electric paper is to bring out some interesting details, which cannot resistance of a metallic wire and the temperature. Although well be obtained from an ordinary gauge. Among these we it has been demonstrated that platinum is a suitable substance may mention the frequency and duration of very heavy showers,
for determining temperatures over a very wide range, not much the great majority of which last only about twenty minutes.
different probably from 2000° C., nevertheless, seeing that each Sixty per cent. of these occur between 1h. and 7h. p.m., and platinum thermometer needs at least to have its constant 87 per cent. occur between June and September. In the yearly specially and carefully determined, not by three, but by a series range the rainfall probability reaches a maximum in the early of observations, it cannot be too strongly urged that this work summer and in the late autumn, while the minima fall in mid.
should in each case accompany the record of results when exsummer and in the first months of the year. In the daily range pressed in platinum temperatures; and no one will deny that to the duration of rainfall reaches a maximum between 6h. and
have these results expressed at once in terms of the normal air8h. a.m., and falls to a shallow minimum at 7h. to Sh. p.m.,
thermometer will permanently enhance the value of the work in after which it rises uniformly to the maximum again. The
such a manner as to amply recompense the extra labour. With various phases are shown both in tabular and graphical form.
the view of helping towards this desirable end, Mr. Dickson Dr. Riggenbach is perhaps best known to English meteorologists
proposes a formula of the form (R+a)=P(t+b), where a, p, b by the success with which he has prosecuted cloud photography.
are constants, and gives reasons for considering it as more repreHERR OTTO BASCHIN contributes to the Verhandlungen der
sentative of the connection between temperature and resistance Gesellschaft für Erdkunde zu Berlin an account of the fitting than any formula hitherto proposed, and just as simple as any. out and departure of Andrée's balloon expedition. The different
An interesting extension to space of n dimensions of Euler's possibilities as to the fate of the explorers are discussed, and the
and Meunier's theorems on the curvature of surfaces has been conclusion reached that there is as yet no reason to give up given by Signor Luigi Berzolari in the Atti dei Lincei, vi. hope of their return. Under the most favourable circumstances the balloon might easily deposit its passengers on a part of
The author proves the following propositions :-Given
in S, a form of n - 1 dimensions, the curvature (of Kronecker) Northern Siberia, from which it would take months to reach
at any point of any hyperplane section is equal to the curvature the nearest telegraph station.
of the hyperplane section having the same trace on the tangent The new number of the Mittheilungen von Forschungs. hyperplane at that point divided by the n– 2th power of the reisenden und Gelehrten aus den deutschen Schutzgebieten con. cosine of the angle between the hyperplanes. The curvature of tains some items of geographical interest. Dr. F. Stuhlmann the normal hyperplane section at O is a maximum when the trace contributes a paper on the German-Portuguese frontier in East of the cutting hyperplane on the tangent hyperplane at O is one Africa, with a new map of the mouth of the Ravuma. In the of the principal sections S, - 2 of the indicatrix, and the sum of same region Lieut. Stadlbaur gives a short account of the Turu the curvatures of any n - 1 hyperplane normal sections mutually district and its people ; whilst First Lieutenant Freiherr von at right angles is constant. Stein describes the Ossa or Lungasi lake, on a tributary of the
DETERMINATIONS of the thermal conductivity of ice by Savaga in the Kameruns.
different observers have hitherto exhibited a remarkable disDIFFERENT minds place different estimates on the intellectual crepancy of results, the values of this coefficient being, accordaccomplishments of the past half-century. In ordinary conver- ing to F. Neumann, 0-34 ; De la Rive, 0'14 ; Forbes, oʻ134 sation the men of the mart will point to an Eiffel tower, a and oʻ128, according to direction ; and, according to Mittchel, suspension bridge, a continental express train, a man-of-war, or 0:30, the centimetre, gramme, minute and degree Centigrade an Atlantic cable. But in a discourse recently delivered in being taken as units. In the Atti dei Lincei, vi. 9, Signor Paolo commemoration of the jubilee of the Sheffield Scientific School Straneo describes a simple method of determining this coefficient. of Yale University, President Gilman remarked that perhaps From observations on two different kinds of ice, taking two the greatest triumphs of the intellect during the last half-century different cubes of each, the values obtained are 0 307, 0-309 for
one kind, o‘312 and 0.313 for the other. A further determina- hung up to dry, care being taken to choose a shady place, as the
The current number of the Annali d'Igiene Sperimental homogeneous amorphous ice the values for the vertical and
contains a note by Dr. Casagrandi on a yeast producing a red horizontal directions were found to be practically equal (0-312 pigment which, in many respects, resembles the one described and 0-308), but homogeneous non-amorphous ice gave for the
by Demme some years ago, and isolated by him from a cheese. same directions o‘328 and oʻ301 respectively in one experiment,
Demme stated that his variety was not endowed with any and 0-325 and 0-308 in another, showing that only ice which is fermentative properties ; that isolated by Casagrandi, on the connot persectly amorphous presents small differences in the co
trary, ferments glucose very readily. This fermentative power efficient of conductivity in different directions.
is not, however, a trustworthy one for establishing differences The physical aspect of the reversal of the photographic between very similar varieties of bacteria, for, as in other cases image is the subject of a suggestive paper by Captain Abney in so in this, Casagrandi has found that Demme's yeast can be inthe Journal of the Camera Club. To investigate the matter, a
duced to ferment glucose if particular precautions are adopted. series of photo-micrographs of sections of films which had been Both Demme's and Casagrandi's specimens are pathogenic to given known exposures was taken. From these sections it is guinea-pigs, rabbits and rats, when subcutaneously introduced seen that the part of the films in which reversal has taken place into these animals; whilst of much interest is the fact that when are markedly different at the upper and lower surfaces. Near grown in milk they are both capable of so modifying the character the upper surface the section shows comparatively fine grains of of this liquid that dogs and rabbits fed with such milk develop silver, whilst at the bottom surface it shows coarser grains. At diarrhrea, and the same symptoms have been observed in babies the top part of the film, where the light has acted strongly, the which had partaken of milk in which this red yeast had been reversal has taken place. At the bottom the light has not acted growing. This yeast appears to be present in our surroundings, much more than usual, owing to the shielding action of the top and may, therefore, at any time make its presence felt by obtainpart. When given areas of the film are examined, the numbers ing access to milk if the latter is left unduly exposed. We of separate silver particles are found to be very much the same already have one well-recognised red yeast, the so-called kosa in both cases, showing that there is a sort of normal number hefe, but Casagrandi does not claim that his variety is anything per volume which is subject to reduction, and that the main more than an offshoot from the second red yeast, known to us difference is in the size of the reduced particles. In the course as the Saccharomyces ruber discovered by Demme some seven of a discussion upon the subject of the paper, Dr. Armstrong, years ago. referring to the sections of the unreversed image, considered
No. 11, vol. iii., of Spelunca contains, among much other that Captain Abney had shown that to be the case which must
cavern-lore, an illustrated account of M. Martel's explorations be the case, and that so long as there was no reversal the
in the British Isles in 1895. particles must be practically as large as the bromide particles, and all of the same dimensions. By showing that the particles In the November number of the Irish Naturalist, Mr. G, H. in the reversed image were so very much smaller, Captain Abney Kinahan urges the importance of a careful study of quartz-rocks, had contributed in an important degree to the solution of the when not metamorphosed, with a view to the recognition of character of the change that took place ; it appeared to him structures that may prove some of them to be of organic origin, that it had been shown that there was in some way a re. like the modern sinter produced by the algæ of hot springs. conversion of the surface of the particle into soluble matter
MR. W. JEROME HARRISON has reprinted, from the that evidence had been adduced to prove that there must be a
Glacialists' Magazine, “ A Bibliography of Norfolk Glaciology," re-transference of the bromine back into the silver at the
on the lines of his similar work on the Midlands. Over four surface, leaving untouched the silver lower down in the particle, hundred papers are catalogued, in approximate order of publiand consequently that when the fixing solution was applied, cation, and short abstracts of the most important are given. the particle became reduced in size.
There is also a list of the Geological Survey maps, and an As article of perhaps no little interest to many persons in
author-index. A reproduction of a photograph of one of the this country, and of some substantial importance to Spanish great chalk-masses in the drift of Runton forms a frontispiece to industries, is the so-called gut from silkworms. This is useful
this useful reprint. for fishing purposes, partly on account of its great tenacity and
To commemorate the incorporation of the University College partly owing to its transparent quality, the line attaching the of Sheffield, a number of scientific papers by members of the hook when in the water not be visible. The manner of College have been brought together and printed in a volume for obtaining this threadlike gut is described in the Journal of the private distribution. The subjects of physical papers included Society of Arts as follows:-After the grub has eaten enough in the volume are :-The influence of carbon on iron, by Prof. mulberry leaves and before it begins to spin, which is during the J. O. Arnold ; the preparation of pure iron by electrolysis, by months of May and June, it is thrown into vinegar for several
Prof. W. M. Hicks, F.R.S., and Mr. L. T. O'Shea ; vortex hours. The insect is killed, and the substance which the grub, aggregates with gyrostatic quality, by Prof. Hicks; functions if alive, would have spun into a cocoon, is forcibly drawn out
connected with tesseral harmonics, by Prof. A. H. Leahy ; super. from the dead body into a much thicker and shorter silken thread.
heated steam-engine trials, by Prof. W. Ripper ; the amount of Two thick threads (from each grub) are placed for about four carbonic anhydride in the atmosphere, by Prof. W. Carleton hours in clear cold water, after which they are dipped for ten or Williams ; and contributions to the knowledge of the Triazole fifteen minutes in a solution of some caustic, for which purpose series, by Dr. George Young. In biological science there are soft soap dissolved in water is used. This serves to loosen a
papers on the comparative intellectual value of the anterior and fine outer skin, which is next removed by the hands while the posterior cerebral lobes, by Dr. C. Clapham; the development workman holds the thread between his teeth. The silk is then of the ovipositor in Periplaneta orientalis, by Prof. A. Denny :
the preparation of marine animals and plants as transparent sented by Mr. William Wethered ; an Arctic Fox (Canis lagolantern slides, by Prof. H. C. Sorby, F.R.S. ; and the shape and pus) from the Arctic Regions, presented by Mr. H. E. Wood ; position of the pancreas and the adjoining viscera, by Prof. C. a Dominican's Cat (Felis dominicanorum), two White-legged Addisən. The editing committee state that the volume “ is pre. Falconets (Murohierax melanoleucus), a White-browed Laughsented as an earnest that the new College may in the future be ing Thrush (Dryonastes sannoi), a Collared Jay Thrush (Gar. distinguished, not only for the number of students it has trained, rulax picticollis) from the province of Foochoo, China, presented but also as a place for the advancement of knowledge.” We by Messrs. C. B. Rickett and J. De la Touche ; four Burrowing accept the token, and from its character we are sure that the Owls (Sprotyto cunicularia) from Argentina, presented by Miss L'niversity College of Sheffield will not be behind in valuable Sandys Lumsdaine ; a Common Chameleon (Chamæleon vui. contributions to science.
garis) from North Africa, presented by Miss M. L. Peake; a The number of cuprous salts at present known is very small
Golden Eagle (4quila chrysetus) from Newfoundland, two in comparison with the large number of stable cupric salts
Black-necked Swans (Cygnus nigricollis, 8 ) from Antarctic that can exist. The isolation of cuprous sulphate, in particular,
America, ased ; a Crested Porcupine (Hystrix cristata), has not yet been effected.
In the current number of the Comptes born in the Gardens. rendus of the Paris Academy of Sciences there is an interesting account, by M. A. Joannis, of some attempts to isolate this salt, which, although unsuccessful, tend to prove that cuprous sulphate
OUR ASTRONOMICAL COLUMN. can be formed under certain conditions. Finely divided metallic copper cligested with a solution of cupric sulphate, as is well
OPPOSITIONS OF Two MINOR PLANETS.—The minor planet known, undergoes no change. If, however, carbon monoxide
Ceres will be in opposition to the sun on the 25th of this
month. (For elements and coordinates see pages 2 and 3 of is led in, a slow absorption takes place, the copper dissolving, Appendix to Nautical Almanac 1897.) Although Ceres is the and the solution becoming decolorised. These facts can be largest of the asteroids, it is interesting as having to give preaccounted for by assuming that cuprous sulphate is formed cedence to Vesta for brightness; the stellar magnitude at which combines with the carbon monoxide to form a compound
this opposition will be 7'1. Ceres is now describing a retroanalogous to that obtained from cuprous chloride. The decom- grade path on the borders of Auriga and Gemini, near
Geminorum, and has therefore a considerable altitude. position of this solution when the gas is removed by the mercury There is also an opposition, on the 26th inst., of one of the pump is somewhat remarkable, for as soon as the pressure is fainter and less well-known minor planets, viz. Gerda, the reduced to about 2 mm. a pellicle of metallic copper forms elements and coordinates for which, as given by M. A. Iwanow, on the surface, and the solution becomes blue, the reaction
of Pulkova, will be found in Astr. Nach., 3458. At the time of between cupric sulphate, copper, and carbonic oxide being in opposition the asteroid will be near to v Geminorum. fact a reversible one and a function of the pressure of the gas. THE TOTAL SOLAR ECLIPSE OF 1900 --Prevision is always
Į a desirable attribute, and to an astronomer it is essential. We From the December Journal of the Chemical Society, we are reminded of this by an account given by Prof. Frank II. derive the following particulars of a paper on the production of Bigelow, in the Monthly Weather Review, of the probable sugars in beetroot, by Friedrich Strohmer :- The opinion meteorological conditions along the path of the total eclipse of expressed thirty years ago by H. Schacht, that the quality of
the sun, in the United States, on May 28, 1900. Beginning beetroots depends on the number of developed leaves and the
with May 15, of this year, and continuing until June 15, so as
to include May 28 centrally, meteorological observations were length of life of the plant, is now shown to be free from objec
made at sixty-six stations distributed uniformly over the portions tions. Sugar is produced in the leaves, either directly as reducing of the States of Virginia, North Carolina, South Carolina, sugar, or from starch or other carbohydrate, and migrates Georgia, Alabama, Mississippi
, and Louisiana, crossed by the through the leaf stems to the root. The production of sugar eclipse track. Observations were made of the general state of depends on the amount of light, and the form and position of
the sky at 8 a.m., 8.30 a.m. and 9 a.m., and also of the state
of the sky near the sun. The results show that the conditions the leaves are of importance. When the sunlight passed through
in the interior of Georgia and Alabama were better than in white or yellow glass, leaf production was vigorous, but with North Carolina, South Carolina, or Louisiana. Apparently it blue or red glass feeble ; and the weight of roots under the would be safer to establish eclipse stations in central Georgia or influence of yellow light was nearly twice as great as when blue Alabama, upon the southern end of the Appalachian mountains, and red light were employed. The percentage of sugar under
where the track crosses the elevated areas, than nearer the
coastline in either direction, north-eastward towards the Atlantic the different conditions was 7:4-8•1 with yellow, 6'4-714 with coast or south-westward towards the Gulf coast. red, and 8:0-84 with blue light. For producing total organic It is intended to repeat the observations during the years substance in beetroot, rays of medium wave-length are the most 1898 and 1899, so as to obtain as good information as possible favourable, but for converting the products of assimilation into
with regard to suitable eclipse stations for the year 1900. sugar, the so-called chemical rays seem to have a prominent role.
CORRECTED POSITION OF THE MOON.-It will be reThe results of field experiments showed that sugar production membered that the Pleiades have been quite recently occulted begin; at an early stage in the leaves, but is greatest from the twice by the moon, once in July and again in October. These beginning of August to the middle of September. Under occultations were specially observed at Lyons, and in No. 22 favourable conditions, there may be a
not inconsiderable Comples rendus, vol. cxxv., M. Lagrula shows that in a series
of occultations of stars by the moon, observed at cpochs accumulation of sugar even later. From the beginning of July, sufficiently near together, it can be supposed that the correcthe sum of the percentages of water and sugar in the roots is tions to apply to the tables of our satellite vary proportionally constant. This, and the fact that the percentage of sugar in the with the times. It is then possible from these to combine the roots increases until the leaves die, indicates that the sugar,
equations of condition supplied by the different phenomena once stored in the roots, remains there. It is only when the
observed. Thus we can obtain with great precision the semi
diameter and the coordinates of the moon at the mean epoch, roots are taken out of the soil and the leaves cut off, that the and even in certain cases her parallax. The two important sugar begins to be used up in maintaining the life of the plant occultations discussed are those which took place on July 23 and in preparation for second year's growth.
and October 13, 1897. The results are given in the following
table, where D and i represents the semi-diameter and the The additions to the Zoological Society's Gardens during the parallax of the moon at her mean distance ; Ax and as the past weeka include an Ocelet (Felis pardalis) from Para, pre-corrections in R. A. and declination, which ought to be applied
d. h. m.
to the coordinates in Hansen's tables, corrected from New- to the west of the geographical north, has been studied for three comb's numbers.
hundred years and is still unfinished. It is a secular variation,
No. of which the period, if definite period there be, must be Paris Mean
of Time 1897
measured by ages, and centuries may yet elapse before the first ja 18 Obs.
cycle which man has watched will be complete. July 23 13 9
15 32-8710-14 indeterminate + 0*30+0+01.-o'i toʻ2 36 In spite of these difficulties attempts are continually being Oct. 13 14 5
15 32.86 +0 24 57' 3".2+10 + 031 +0'02.+0'550'4 29 made to draw from the facts at our disposal some more definite A New FORM OF MIRROR FOR A REFLECTING TELESCOPE. information as to the causes of terrestrial magnetism ; to foretell - During the dedication exercises held in connection with the the future from the present ; to trace the connection between Yerkes Observatory, Dr. C. L. Poor advocated and exhibited a
the magnetic state of the earth and the constitution of the sun reflecting telescope in which the mirror is a portion of a para.
or of the earth itself; and I propose, therefore, to bring before boloid of revolution cut from the surface near the extremity of you some of the theories and speculations which are now the latus rectum. The reflected rays then being at right angles attracting the attention of those who take special interest in to the incident rays, no dome would be required for such a
this science. telescope, and there would be no secondary mirror. This form
The fundamental fact, or rather series of facts, from which of telescope was, however, recommended by Prof. Pickering magnetic state of the surface of ihe earth. To determine this,
we have to begin our investigation is a knowledge of the more than sixteen years ago (NATURE, 1881, August 25); moreover, Prof. Schaeberle shows in the Astronomical Journal, No.
observations have for many years past been made at many 419, the inefficiency of such an instrụment, from the following different places, at sea and on land." The general result is a considerations. Let L denote the distance from the focus to the matter of common knowledge. The compass needle points apcentre of the mirror, which is evidently inclined about 45° to the proximately north and south, and dips from the horizontal line of sight. If D denotes the minimum diameter of this towards the magnetic poles of the earth. elliptical mirror, the maximum diameter must be D sec. 45° if a
The first and simplest hypothesis that will serve as a rough circular cone of rays is to be used. The linear distance from approximate explanation of these facts, is that the earth itself the focus to the nearest and most distant points of the mirror is uniformly magnetised, or that there is at the centre of the will then be approximately
earth a small but very powerful magnet by which the compass
and the dipping needle are controlled. Least distance L D sec 45:
If this suggestion were adequate, we should be compelled to Greatest distance L + } D sec 45°.
assume that the axis of the magnet was inclined to the axis of L If we assume
the earth, for the magnetic and geographical poles do not = 1, the greatest distance divided by the D
coincide. It would further follow that at the magnetic poles, least distance becomes 1'-22.
where the dipping needle is vertical, the magnetic force, which This quantity is approximately the blurring factor for the determines the position of the needle, would be of maximum given ratio of focal length to aperture for this form of instru. intensity. ment. For a star which is only 5' from the optical axis of the But here the simple hypothesis breaks down. The distributelescope, and in a place containing the longer axis of the tion of terrestrial magnetism is more complex than that which mirror, the image will, therefore, be a line no less than 66", or can be thus explained. It is true that there are two magnetic more than a minute of arc.
poles, but the directive force is not greatest where the needle is Exactly at the focal point this star image will be a point, but vertical. On the contrary there are in each hemisphere two for all other positions of the image ihe definition will be other points, generally called magnetic foci, at which the force unworkable.
is a maximum.
It is thus evident that the magnetic system of the earth might be better represented by supposing that there are within it iwo
magnets inclined both to each other and to the geographical RECENT RESEARCHES ON TERRESTRIAL
axis, that the foci indicate the directions of these axes, and that MAGNETIS.V.1
the magnetic pole or point where the needle stands vertical is THE science of terrestrial magnetism has on one previous determined by their joint action. Mr. H. Wilde attempted to
occasion formed the topic of a Rede Lecture. Twenty. imitate the magnetic state of the earth by the aid of a duplex five years ago Sir E. Sabine delivered a discourse on this subject, arrangement of this kind, but even this was insufficient. He with which his name will always be honourably connected. was compelled to supplement it by covering with thin sheets of The length of time which has elapsed may perhaps justify a iron those portions of the globe which correspond to the oceans, return to the same theme, though it must be admitted that now, and with this modification he succeeded in making a capital as then, the study of the magnetic properties of the earth is magnetic model of the earth. in an early stage of development. It is true that considerable For the moment, however, I will not follow up the line of advances have been made in the theory of the nature of inquiry thus suggested, but will only draw attention to the fact magnetism itself, and of its connection with electricity; but that, in spite of all these complications, mathematical analysis when we attempt to apply theory 10 explain the actual con- supplies us with the means of answering certain questions as to dition of the earth progress is at once checked by difficulties, the magnetic constitution of the earth, without the aid of a clear many of which have hitherto proved insuperable.
We have no mental picture of the causes to which that magnetic state is due. real knowledge of why the earth is a magnet, no real knowledge Whether there be one or more independent magnetic systems as to why its magnetic state is continually changing, and thus within the globe, whether some portions are more magnetic we are compelled to spend long periods of time in collecting than others, are points upon which at present we have but little facts, which, though their number and complication oppress us,
information, but there are a few facts from which we can argue are still insufficient to answer some of the simplest questions with the knowledge that the foundations of our investigation that an inquirer, approaching the subject for the first time, would be sure to ask. Terrestrial magnetism is in this respect Magnetic forces can be produced only by magnetised matter, in the same stage as that occupied by astronomy during the or by electric currents, and these may either exist within the centuries in which the data were accumulated on which Kepler globe or be external to its surface. Some of the currents, how. and Newton worked. We have a certain grasp of the facts, but ever, may be both internal and external in the sense that their cir. have not yet found the thread of theory which binds them cuits pass partly through the rocks and partly through the air, and together.
that at certain points they traverse the surface from earth to air And in one respect the magnetician is less favourably or from air to earth. Thus the first important question with which situated than was the astronomer. The rapid repetition of the investigator is confronted is : Are the forces which act upon the principal astronomical events made it comparatively easy the compass produced within or without the globe ? and, if the to discover the laws which those events obey ; but, though magnetic forces are in part due to electric currents
, are all these some magnetic phenomena run through their courses in a day, currents wholly internal or wholly external, or do some of them a year, or a short period of years, the greatest change of all, Aow in part within and in part without the earth? that which causes the magnet io point now to the east and now With regard to the first inquiry, the great mathematician 1 The “Rede Lecture" delivered in the Senate House, Cambridge, on
Gauss furnished us with a method by which, if our knowledge June 9, by Prof. A. W. Rücker, F.R.S.
of the magnetic state of the surface of the earth is sufficiently