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least one thing is certain the writing-fluid used by specific gravity of dilute hydrochloric acid is given the ancient scribes for such records as the foregoing wrongly on p. 208. In the historical introduction we must have possessed in a high degree the property of are told, apropos of a certain document (p. 11), that durability.

" it was probably written at the end of the sixteenth In one form or another, the basis of these early century by a man past middle age, who learned to writing-fluids was carbon. For example, Chinese ink, write just about the time that Shakespeare was born the so-called “ Indian”ink of the modern artist, which (1504).” At first it seems an unnecessarily cautious according to the native historians has been made since understatement to call such a man "past middle age," 2600 B.C. or thereabouts, was at first a vegetable but a little reflection shows that it is those kittle cattle varnish, and later a mixture of lampblack and glue. the figures that are to blame. Inks containing gallate of iron did not come into use The book is a serviceable addition to the literature until a much later period. Thus Sir Humphry Davy, of chemical technology.

C. SIMMONDS examining some documents recovered from the ruins of Herculaneum,“ looked in vain amongst the MSS.

OUR BOOK SHELF.
... for vestiges of letters in oxide of iron," and he
concludes that the Romans up to the time of Pliny

By Hans Driesch.
Naturbegriffe und Natururteile.
Pp. viii +239.

(Leipzig: Wilheim Engelmann; had never used “ink of galls and iron " for writing

London : Williams and Norgate, 1904.) Price 4s. purposes. Gradually, however, in the early centuries net. of the Christian era, there came a transition from This book deals chiefly with three topics. Starting carbon inks to those containing iron; and Blagden, in on a Kantian basis, it seeks to state the a priori prin“ Some Observations on Ancient Inks,” communicated ciples of pure physical science. (A priori is conto the Royal Society in 1787, records that the writing

veniently defined as independent of the amount of

Next,

experience.”). fluid employed in various MSS. on vellum, dating from energetics' are discussed, and their relation on the

the leading principles of the ninth to the fifteenth centuries, was an iron and one hand to the a priori principles of pure physical gall ink. Somewhat earlier than the date of Blagden's science, and on the other hand to the ordinary laws paper logwood began to find employment as a con- of thermodynamics. Incidentally, the “laws" of stituent of inks, and soon after the middle of last conservation (of substance and the like) are examined, century came the next notable modification, namely, the results attained are carried over to a discussion of

and entropy has a good deal of attention. Last of all the use of aniline dyes in the manufacture of both biology. The point of view is neo-vitalistic. It would black and coloured writing-fluids.

be hazardous to say that the author has run to earth Of these and other matters bearing upon the history, the x which is the object of all our search, the vital composition, and methods of preparing the various principle or whatever other name may be applied to kinds of inks, Messrs. Mitchell and Hepworth have it; the term which he uses is the blessed word

entelechy. much to tell us in the volume under notice. They

Herr Driesch is well known to be at his best a have brought together, and made convenient for clear, original and suggestive writer. Much of the reference, material that has been hitherto chiefly present work is excellent, but we doubt if the last scattered amongst periodicals and isolated dictionary eighty pages are either clear or convincing: Perhaps articles. In so doing they have saved their con

one would require to read the author's other works

in order accustom oneself to his point of temporaries some labour, and earned for themselves much gratitude.

view and his independent modes of statement. He

is occasionally unsatisfactory as well when dealing The book is divided into three sections. The first with the theories of others, for example, with Prof. of these deals with writing inks, including those of Clerk Maxwell's “sorting demon." The discussion which carbon, tannin, logwood, and aniline occurs under the heading “ Declarations of Physicists spectively form the characteristic ingredients. It

regarding Biological Subjects," and Herr Driesch

almost seems at times to suppose or to imply that the comprises chapters upon the sources of the tannin

conception may have been formed in order to limit materials, the chemical nature of iron-gall inks, and

the second law of thermodynamics to inanimate bodies. the best methods of examining both the fluid itself and True, Lord Kelvin's statement of the second law has the characters on the written page.

Printing inks the words “in inanimate material." But Lord form the subject of section ii., in which an interesting

Kelvin's declaration is explicit (" Popular Lectures and chapter treats of colour work, including three-colour

Addresses," 1889, vol. i. p. 141) :-“ The conception

of the ‘sorting demon' is merely mechanical and is printing and inks for use in the production of cheques of great value in purely physical science. It was not and bank-notes. In the concluding section there is a invented to help us to deal with questions regarding description of inks intended for miscellaneous pur- the influence of life and of mind on the motions of poses; these comprise copying, marking, safety, and matter." On p. 103 the accurate reference to Helmsympathetic inks, and fluids for writing on glass,

holtz's work is-Ostwald's Klassiker Nr. 124, p. 3o.

Anm. wood, ivory, or leather. Many formulæ are given, some of which the authors have personally tested, and Higher Text-book of Magnelism and Electricity. By the work closes with a list of English patents relating

R. Wallace Stewart, D.Sc. Being vol. iv. of " The

Tutorial Physics.” to the subject.

Pp. viii +672. (London : W. B. Despite occasional incoherency of style, the two : We have several times noticed this work as successive

Clive, University Tutorial Press.) Price 6s. 6d. collaborators have produced a useful and attractive

editions have appeared, and can speak as appreciatively little volume. One or two slips may be pointed out; of it as we have on other occasions. The present thus the equation on p. 101 is incomplete, and the volume is based on the older one, but it lias been wholly

to

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Price 155.

re-cast, and a very considerable quantity of new matter vided that life is a physical entity, it must be either has been added in view of the rapid advance which matter or energy” (p. 16). “If it is a form of matter, has been made in electrical theory in the last few it must weigh something” (p. 17). But what if it yrars.

were ether? (4) “ The living plant opens out a new In this edition the author has followed several other path in which physical law can operate” (p. 39)—" it text-books in laving stress upon the importance of has, in a sense, directed the energy into special the electric field as the real seat of the energy of an channels ” (p. 38). But is this a differentia of life? electric circuit. It should be clearly brought out, how- Surely to one acquainted only with other manifestever, that part of the energy must flow in the con- ations of energy the path opened out by the dynamo isductor, following there, as elsewhere, the direction of as new as anything can be. the equipotential surfaces; the forward flow is: how- Glossary of Geographical and Topographical Terms. pver, in the dielectric itself. The figures exhibiting this flow of energy on pp. 344, 525, and 528 are very

By Alexander Knox, B.A., F.R.G.S. Pp. xl+432. tar from satisfactory. It is sufficient to point out that This work, which is intended as a supplementary

(London : Edward Stanford, 1904.) in every ordinary case of steady transfer the lines of

volume to Stanford's “ Compendium of Geography force are convex forwards; indeed, if it be borne in

and Travel,” is evidently the outcome of a vast amount inind that in accordance with Poynting's theorem the

of industrious research on the part of the author. The flow of energy takes place at right angles to the lines

amount of labour involved in the collection of some of force, there would be energy flowing out from and not into a conductor if the lines were as shown.

10,000 geographical terms derived from the most Too much care cannot be exercised in the construc- imagined, and it can only excite our admiration that

diverse languages all over the world can readily betion of diagrams. They catch the eye; and just as nothing is better than a good diagram for inculcating by a single individual. The book will be a decided

so much should have been successfully accomplished truth, nothing can be worse educationally than one that is slipshod.

boon to readers of works of geography and travel, This remark applies equally to a figure illustrating who, in the absence of deep linguistic' attainments, the action of the keeper of a magnet on p. 227, where

must constantly be puzzled by the terms employed in about twice as many lines of " force" are shown in

the place-names of foreign countries. It will also be

valuable to the more scientific geographer as supplyare the keeper supposed to be independently magnetised? ing a useful basis for the complete dictionary of geoAgain, on p. 401, if the equipotential lines on the

a

desideratum. Mr. Knox's book, useful as it is, can plate exhibiting the Hall effect were really as shown, some of the current would flow over the edges of the

hardly be said to supply this need, being concerned conductor.

rather with the general and popular, than with the

scientific and technical usage of geographical terms. This slovenliness is almost wholly confined to the figures. The text is exceedingly lucid and painstaking

It was undertaken in the first instance, as the author in the endeavour to give a student a sound knowledge explains, with a view to elucidate the terms in use in of physics. The large number of worked out examples, extra-European countries, and this object it certainly

fulfils with success. which have always been a distinguishing feature of

European geographical terms, the book, have no doubt contributed largely to the

which naturally include the majority of those with appreciation which it has received, especially from

which the scientific geographer is concerned, are less

fully dealt with, and we not only miss many such those who are compelled by circumstances to work

technical terms without a teacher..

“ Karst," “ Kar," “ Horst," Schrund,"

“ Aven” (to take a few only at random), Life and Energy-Four Addresses. By Walter but we find little attempt made at discrimination

Hibbert. Pp. xiv + 182. (London : Longmans, between the terms in use for closely allied features, or Green and Co., 1904.) Price 28, 6d. net.

at the definition of nice shades of meaning, such, e.g., The thesis of these four addresses-originally delivered as are involved in the words “ dale” and “dell,” both at the Polytechnic Institute, London—is that life is of which are explained merely as a valley.” Many not matter, is not energy, but an unceasing non- English local terms are missing, and the definition of factorial directive control of energy and its transform- others is not always quite satisfactory. On the other ations. “ Directive control," i.e. in the same sense hand various Spanish topographical terms are carefully in which temperature ” in the case of heat, or explained, and the recent definitions by the Inter"potential" in the case of electricity, controls the

national Commission for the Study of the Sea of the direction in which the energy shall flow. Non

main features of suboceanic relief are correctly given. factorial," because while temperature, potential, and But the special value lies in the fact that the inthe like are factors of energy, life is not a factor.

formation supplied is just that which is most out of Mr. Hibbert puts most of his points clearly, and

reach of the ordinary reader, terms derived from the much of what he says has considerable force. But it languages of Africa, Asia, and the less known parts is doubtful if the range of ideas within which the book

of the world generally, being particularly well repremoves is adequate to the problem. The main position sented. The introduction includes some useful hints, is not unassailable, and the deductions from it in re

by Dr. A. H. Keane, on the laws of interchange of gard to morals and religion are occasionally fanciful. letters in various languages.

To descend to details. (1) It is difficult to see how the terms factorial and non-factorial describe precisely

Blackie's Handy Book of Logarithms. Pp. 128.. the difference between the directive control of energy

(London : Blackie and Son, 1904.) Price 25. manifested in inorganic and in organic bodies re- Tier- und fünfstellige Logarithmentafeln. Pp. 24. spectively. The discussion on p. 50 rather begs the (Brunswick : F. Vieweg and Son, 1904.) Price 0.80 question. (2) In describing God's directive control as mark. being purely non-factorial, in saying (p. 144), “ It is In order that mathematical tables intended for common not the office of prayer to seek any direct disturbance use may serve their purpose, it is essential that great of the course of material nature, is but “its office is attention be paid to the labour-saving arrangements to secure a renewed faith in non-factorial control,” which authors have from time to time introduced, such Mr. Hibbert lays himself open to the retort, “ Then as the careful grouping of the figures in rows and non-factorial control is no control at all.” (3)“ Pro- columns, the use of varied type or of differently

as

66

not

" thick

coloured inks, marginal or thumb indexes, proportional

LETTERS TO THE EDITOR. differences, inverse functions, &c. On opening [The Editor does not hold himself responsible for opinions Blackie's “handy" volume, the reader will be dis

expressed by his correspondents. Neither can he undertake appointed to find that the compiler of the tables has to return, or to correspond with the writers of, rejected paid little attention to the points enumerated above. manuscripts intended for this or any other part of NATURE. A table of six-figure logarithms of four-figure numbers No notice is taken of anonymous communications.] occupies twenty-two pages; the average difference for

The Heterogenetic Origin of Fungus-germs. each row of figures is given, but there is no room found for proportional differences, so that the taking out of An attempt has been made in VATURE (December the logarithm of a five- or six-figure number involves 22, 1904, p. 175), By Mr. George Massee, of Kew, to an irritating calculation. Anti-logarithms are

question the validity of my conclusions because of certain included, but there is a table of hyperbolic logs.

observations of his own of a totally different kind, which

have little or Sixteen pages are allotted to tables of natural and

no bearing upon what I have brought

forward. logarithmic functions of angles, for increments of onesixth of a degree, without differences. Other tables produces exceedingly minute colourless conidia which are

What he says is this :-Dematium pullulans of de Bary include reciprocals, squares and square roots, cubes and most widely distributed and are capable of passing through cube roots, circumferences and areas of circles, heights

filter

paper. Under normal conditions," he and areas of circular segments, and rhumbs in degrees. adds, these minute conidia on germination form delicate There is an appendix giving some simple mensuration hyaline hyphæ which give origin to a Cladosporium. If rules, some old-fashioned practical geometry, and

cultures of these conidia become infested with bacteria definitions of the functions of angles, not as ratios, but that form Zooglæa, the hyphæ become invested with a as lengths.

comparatively thick, brown cell-wall, and form either comThe German tables are specially suitable for use in

pact masses of cells or irregular hyphæ consisting of short the chemical laboratory. The main feature is an

cells, constricted at the septa, exactly as shown in Dr.

Bastian's Fig. 12." He then refers to an illustrated paper eighteen-page table of five-figure logarithms of fivefigure numbers, arranged, with proportional differ

in the Kew Bulletin for December, 1898, in which he has ences for each row of figures, like the four-figure

shown this process as it occurs in a certain disease of

Prunus ja ponica. He thinks his observations exactly logarithms contained in the first two pages. The

illustrate some of the facts which I have brought forward, collection of physical constants at the end is such as while I, after carefully reading his paper and studying a chemist would be likely to require. There are no his illustrations, think they are altogether beside the mark. anti-logarithms, nor is there a marginal index. The He supposes the widely distributed conidia are not only size of page is ample, allowing of bold and effective present in the hay infusion (which of course they mar type.

be), but that they are able to pass through two layers Second Report on Economic Zoology: British Museum

of very fine Swedish filter paper (not merely " thick (Vatural History). By Fred. V. Theobald, M.A.

paper, as he loosely puts it). Looking to his Fig. 5 and

the size of the conidia there shown, this, I think, is more Pp. X+ 197. (London : Printed by Order of the

than doubtful. It is, however, altogether immaterial Trustees of the British Museum, 1904.) Price 6s.

whether such conidia are present in the original har inThe recent development of British Museum activities fusion and are able to pass through the filter used by me in the line of economic zoology, for which the insight or not, because the next necessary step in his suggested of the director is largely to be thanked, is re-expressed explanation is altogether wanting in my observations. in a second report, following quickly on the heels of This step is that the conidia assumed to be present shall the first (see NATURE, January 28, 1904, vol. lxix. produce delicate hyphæ, and that these hyphæ, coming into p. 290). We congratulated Mr. Theobald on his first

contact with masses of Zooglaa, shall become invested report, and we repeat our congratulations, for the

with a comparatively thick, brown cell-wall, and form volume does credit to his energy and ability, and to

either compact masses of cells or irregular hyphæ consistthe expertness of those inside and outside the national

ing of short cells constricted at the septa.' But I had museum who have given him assistance.

already privately assured Mr. Massee that all the phenoEveryone

mena which I have described may be witnessed without who has had even a little experience of the amount of

its being possible to meet with a single hypha of any work which is often required in order to answer kind or a single one of the thick-walled, brown cells to apparently simple questions from outside will which he refers.' Yet for his explanation to have ans appreciate the skill which this report displays. The weight delicate hyphæ" should always be seen in relavolume contains a large part of the information tion with the Zooglæa masses, and as for the “ thickfurnished by the director of the natural history depart- walled cells" which are then formed being exactly like ments of the British Museum to the Board of Agri

what I have shown in my Fig. 12, I can assure Mr. culture and Fisheries between November, 1902, and

Massee he is absolutely mistaken. What I have repres November, 1903, besides replies to other correspondents

sented in that figure are colourless products of segmentand some special notes of present-day interest. The

ation of a Zooglæa mass (wholly unlike the colourless British Museum of Natural History is not only one

conidia shown in his Fig. 5) which speedily assume a of the greatest world-treasure-houses of scientific of delicate hyphae, at once grow out into mycelial filaments

brownish-black colour, and then, without any intervention material, it has also, in its staff, an almost unrivalled of the same colour. In accordance with his explanation, wealth of learning, and we cannot refrain from giving the production of delicate colourless hvphæ should be the expression to the widespread gratification that these commonest thing possible, and should always be met with resources of material and knowledge are now being at an early stage of the changes that I have been des utilised in behalf of the practical queries of the nation. scribing ; but, as a matter of fact, nothing is more re The volume deals with mosquitoes, sheep scab, weevils,

markable than the rarity with which any of the myriads aphides, wire-worm, mites, leather-jackets, warbles, of Fungus-germs produced in a bacterial scum undergo ring-worm, liver-fluke, and a hundred other economic- a further stage of development, with the production of allı interesting pests—and always in a way that leads hyphæ either colourless or coloured, and I can assure us to respect Mr. Theobald's wide knowledge and

Mr. Massee that he might work for three weeks or practical shrewdness. We hope that there will be

more with such infusions as I have described without many such reports, for they are of a kind that enrich

finding a single specimen at all comparable with my the nation as well as science. That they also con

Fig. 12. seems deplorable that in regard to such an tribute to art may be illustrated by the report on the subsequently sent to NATURE. In this reply I asked him to come as:

1 This was in reply to a private letter to me very similar to that she grub, causing damage at Rve Golf Links.

taamine my specimens for himself, which he did not do.

cram

an

important subject as the reality or unreality of hetero- usual grammar papers, and, in conjunction with a friend genesis, persons like Mr. Massee, who could speak authori- similarly circumstanced to myself, I set to work to tatively, should not think it necessary to make personal

these by as
" scientific" methods as

we could observations, and should be content to offer in reply to devise, in order to pass with as little waste of time as real and prolonged work only loose explanations which possible. will not bear any serious examination.

Purchasing a copy of Wordsworth's “ Primer of Greek A further instance of the same lack of care is afforded Grammar, we read the nouns, adjectives, and the active in the last sentence of Mr. Massee's letter. Referring voice of Tuntu--no more, and then started on the preevidently to my remark (NATURE, November 24, 1904, scribed books. These we translated by aid of a good p. 77) as to the very different products that may be met lexicon, word by word—thus learning the parts of the with in the scum forming on an infusion made from irregular verbs, which form a favourite subject in the unripe grasses as compared with that forming on

grammar papers. Having been once through the books ordinary hay infusion, he says :—“As these fungi only by this method, we procured the translations, and read develop on fading leaves it was not to be expected that

these through five or six times, in order to become so they would appear in infusions of young grass." This

familiar with the subject-matter of the books that we sentence must have been penned without the writer having could translate most passages easily at sight after making taken the trouble to look at p. 87 of my “ Studies in out the leading words in them. Heterogenesis," to which reference was made when I

The actual time expended by us in the preparation of directed attention to the differences in question. Had he Greek for the examination was carefully recorded, and done so he would have seen how little he had explained

amounted to 105} working hours, and we passed the the differences noted on that and on the following page, examination in the second class, with, I believe, a conand he would also have seen that the most striking differ- siderable margin of safety even in Greek. I need hardly ence recorded is the complete absence of Zooglæa masses (spoken or there as “ areas ') in the scum forming on

add that my present knowledge of the language is nil.

JOHN C. WILLIS. infusions of unripe grasses. Of course if the Zooglæa Royal Botanic Gardens, Peradeniya, Ceylon, masses are not there it is easy for me to understand the

December 28, 1904. absence of the Fungus-germs which, as I maintain, are produced therefrom. This point, as well as others in Mr. Massee's letter,

Polyhedral Soap-films. shows the great importance of bearing in mind two wholly distinct aspects of my observations, corresponding with

The fact that polyhedral wire frames can be used for different stages in the processes described. We have to do

the purpose of forming films across them is well known, (1) with the growth, the individualisation, and the pro

but there are some features of this subject, which I have cesses of segmentation taking place in masses of Zooglæa.

investigated, which may be of interest. We have also to do (2) with the question of the ultimate

If a frame of wire representing the edges of one of the destination, or the transformation, of the products of such

simpler polyhedra, such as a cube or octahedron, is dipped segmentation. These are two parts of the subject which

into soap solution, then on taking it out it will have films are to some extent distinct, and are well worthy of further

attached to its edges and meeting roughly at a point in separate consideration.'

the centre of the figure, forming a number of pyramids In conclusion I would ask, Why do the bacteriologists

standing on the faces of the figure. If, however, a more not tell us what they know about Zooglæa-whether they

complex figure, such as the rhombic dodecahedron or the are or are not aware of its developmental tendencies, and

eicosihedron, be taken, then the effect will be quite different; why it should undergo processes of minute segmentation,

the film will then simply cover all the faces except the unless such processes are a result of an organising tendency

one which was drawn out of the solution first. The former destined to have some definite outcome? Why, again,

thing will happen if the area of the (n-1) faces is greater should it or its segments so often tend to assume a brown

than that required to form the pyramids, while the latter

will occur if the reverse is the case. colour, while it is still nothing but Zooglæa, either segmented or unsegmented? Again, why, if the brown

If, now, in the case of the cube, for instance, after the Zoogleea does not yield the brown Fungus-germs, should

pyramids have been formed, a film be applied to one of there be this constant association of myriads of brown

the faces, then a certain amount of air becomes entirely Fungus-germs (in the absence of hyphæ) in association

enclosed by film, and the bubble so formed settles in with brown masses of Zooglæa? How can they explain,

the centre of the frame, forming roughly a cube suspended other than I have done, the actual organisation of a

in the frame by twelve sheets of soap-film. On closer inZoogleea mass, and the stages by which the brown Fungus spection, however, it will be seen that the faces of this cube germs seem to be formed therein?

What process of

are convex, thus showing that the air in it is compressed. * infection" in a filtered hay infusion contained in

By inserting a tube this cubical bubble can be inflated or closed pot could cause thousands of small Zooglæa masses

reduced in size, all the time retaining its convexity, so to go simultaneously through similar processes of this

that if thus left in communication with the air it will kind-producing myriads of brown Fungus-germs-when

collapse of its own accord. A little consideration shows not a single hypha is anywhere to be found, and when at

the reason for this, namely, that three films meeting one first no Fungus-germs are to be met with outside the

another cannot be in equilibrium unless their planes are Zooglæa masses themselves? I trust the bacteriologists

inclined to one another at 120°, since the tensions in all will vouchsafe to give us some information on these points,

three are equal. But since the dihedral angle of a tetraor, if they cannot reasonably explain them, that they may

hedron, cube, or octahedron is less than 120°, therefore in be induced to work at the subject, and satisfy themselves

these figures the internal polyhedral film must always have that something important can

be learned concerning

convex faces. bacteria, even though it be outside their laboratories and

From this I expected to get an exact polyhedron with by methods other than their own.

plane faces in the case of the rhombic dodecahedron, since H. CHARLTON BASTIAN.

its dihedral angles are all 120°. On trying this it was

found to agree remarkably with my assumption, only, as Compulsory Greek at Cambridge.

may be gathered from what has gone before, it was not

quite so simple to obtain the central bubble as in the former As a corrective to much vague discussion, perhaps the

After the (n-1) faces had been covered with film following record of facts may be of interest.

the figure was again immersed so as to displace about oneEntering the University of Cambridge in 1886, entirely half the air contained in it, and while thus immersed it ignorant of the Greek language, I was, of course, obliged was turned round so as to cover the one open face with to pass the “Little-go" in order to proceed to the natural

liquid. On withdrawing it there was seen the plane-faced sciences tripos. The Greek subjects prescribed were the rhombic dodecahedron. The same result can be obtained Gospel of St. Mark, the Pluto of Aristophanes, and the by applying a film to the nth face and then exhausting

1 My further observations on this subject will be found in the February some of the enclosed air by means of a tube. By using a number of the Arnals and Magazine of Natural History.

tube, as in the former cases, the bubble can be enlarged

a

case.

on it.

razor.

or reduced at will by blowing or suction, and it will metal support to which it is attached. Now the deretain its size constant when placed in open communication flection in question depends only on the shape and size with the outer air by means of this tube. This is, of course, of the leaf and of the metal support, and on the electrothe only plane-faced polyhedron which can thus be formed,

static potential of the system, so that the rate of faces, edges and vertices being entirely made out of soap films. If, on the other hand, a figure has its dihedral

collapse of the leaf measures the rate of decrease of angles greater than 120°, then the internal bubble will

the electrostatic potential. But what we wish to have concave faces, and will, if placed in communication

measure is the current or rate of alteration of electric with the outer air, increase in size until it coincides with charge, and this is equal to the rate of decrease of the faces of the frame, and will then be kept in equilibrium potential multiplied by the electrostatic capacity of the by their rigidity. This I verified in the case of the system. Thus for a given current the rate of moveeicosihedron.

ment of the gold leaves is greater the smaller the There is one important law which must be mentioned. capacity of the system, For a sensitive instrument it I found a certain irregularity in the behaviour of the films is therefore absolutely necessary to have the parts in the case of the octahedron and rhombic dodecahedron.

which are metallically connected with the gold leaf This was due to the fact that two films cannot cross one as small as possible. another at right angles, a law which can be put to the test by placing two plane loops covered with film at right considerable amount of patience, especially from the

Cutting gold leaves is a process which requires a angles, when a small lanceolate film will be formed making beginner. The process I always adopt is to take a two curved lines of intersection with the film on the loops, instead of allowing them to intersect in a single straight plate of glass and lay a sheet of smooth note paper line. In the case of the rhombic dodecahedron this slightly

On this the gold leaf is spread out flat by blowmodifies the form of the internal bubble, introducing a

ing gently if necessary, and is cut by means of a small edge and a little curvature at each of the acute

To do this, all except a narrow strip at the vertices. This defect causes a serious convexity if the edge is covered with a second sheet of note paper, the bubble is small, but in general we have double curvatures straight edge of which is pressed down with the at the points in question, the remaining portion of each fingers so as to hold the gold leaf. A fine strip outface being plain while the figure retains the form of a side the edge of the paper is then cut off from the leaf rhombic dodecahedron.

W. F. WARTH.

by dragging the razor gently backwards parallel to

itself and to the edge of the paper. It is not necessary Reversal of Charge from Electrical Induction Machines. to exert any great pressure during this operation, but

The reversal of the poles of a Voss machine by giving a little practice will be necessary to get into the way some turns in the wrong direction, as observed in NATURE of doing the saw-cut stroke at the proper speed. Mr. of January 5 (p. 221), is not an unknown phenomenon. It C. T. R. Wilson has succeeded in this way in cutting is described in my paper

Essai sur la Théorie des uniform strips one-tenth of a millimetre across, but Machines électriques à influence (Gauthier-Villars, Paris, for most purposes strips one millimetre wide are good 1898), p. 38, together with a much more trustworthy and enough. In working with gold leaf much trouble simpler means--an improvement, in theory and in fact. This consists in discharging by hand, at the same time,

will be saved by working in a room which is free from both the inductors of the fixed disc. Then the reversal is

draughts and disturbances generally. invariably observed without stopping the machine.

For the metal support to which the gold leaf is V. SCHAFFERS.

attached it is convenient to use a piece of wire of Louvain (Belgium), 11 rue des Récollets.

about the same diameter as the thickness of the gold leaf. To fix the leaf on to the wire it is sufficient just

to moisten the latter at the point of attachment with THE CONSTRUCTION OF SIMPLE ELECTRO.

the tip of the tongue; on allowing the end of the SCOPES FOR EXPERIMENTS ON RADIO: gold leaf to come in contact with the very slightly

moist wire it will be found to attach itself sufficiently ACTIVITY.

firmly for all that is required of it. For obvious reasons THE

HE electrical method, where it is applicable, is the cutting and mounting of the gold leaf should be

now by far the most sensitive method of detect- the very last operation in the construction of the ing small quantities of matter; and the recent advances electroscope. in physical science made by the method of measuring In constructing an electroscope it is of the utmost small leakages of electricity, especially in connection importance to have trustworthy insulation. When the with the phenomena of radio-activity, have excited a apparatus has not to be raised to a high temperature, very general interest in the experimental arrange- and great mechanical strength is not required, sulphur ments employed. The writer hopes that the follow- is a long way better than anything else for this puring account of simple electroscopes for this kind of pose. Generally speaking, it is better to have as small work will be found to be of a practical nature and a quantity of insulating material as possible in order of service to those who, though unfamiliar with many to diminish irregularities caused by the superficial of the devices in general use in a physical laboratory, charging up of the dielectric. Suppose we wish to are nevertheless desirous of making quantitative ex- insulate the wire carrying the gold leaf from another periments on radio-activity or some other subject where wire which supports it mechanically we should proceed the electrical method is employed.

as follows :-Take a porcelain crucible and gently In general the final shape of the instrument will heat a quantity of pure flowers of sulphur in it until depend very much on the purpose for which it is re- it just melts and forms a clear yellow limpid liquid. quired; in fact, it is one great advantage of the gold. It is important that it should not be heated so strongly leaf electroscope that it can usually be fixed up in as to become dark coloured and viscous, as this appears any odd corner of the apparatus which happens to be to diminish its subsequent insulating properties. The convenient. There is, however, one part of the end of one of the wires is then dipped into the liquid apparatus which is always the same in sensitive instru- sulphur, when a coating of sulphur forms on the wire. ments, and that is the gold-leaf system itself. Before This is allowed to cool until it has solidified, and the describing this it will perhaps make things clearer operation is repeated a number of times until a bead if we consider for a moment one or two points about of sulphur like that shown in Fig. 1 A has formed on the theory of the instrument.

the end. The end of the other wire is now heated What we observe usually is the rate of decrease of gently in the flame and applied with a slight pressure the deflection of a charged gold leaf from a vertical to the point a, when it melts its way into the su!ohur;

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