Pestalozzianum Zürich Archivbureau der Schweizerischen permanenten Schul.

Philosophical magazine online

. (page 1 of 52)
Online LibraryPestalozzianum Zürich Archivbureau der Schweizerischen permanenten SchulPhilosophical magazine → online text (page 1 of 52)
Font size
QR-code for this ebook


This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project
to make the world's books discoverable online.

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject
to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books
are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.

Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the
publisher to a library and finally to you.

Usage guidelines

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to
prevent abuse by commercial parties, including placing technical restrictions on automated querying.

We also ask that you:

+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for
personal, non-commercial purposes.

+ Refrain from automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the
use of public domain materials for these purposes and may be able to help.

+ Maintain attribution The Google "watermark" you see on each file is essential for informing people about this project and helping them find
additional materials through Google Book Search. Please do not remove it.

+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner
anywhere in the world. Copyright infringement liability can be quite severe.

About Google Book Search

Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web

at http : //books . google . com/|



OF THB

No _ <^J^^S^ ,[

Division ,f

' iii

Range |

Shelf. : , ;

Recdved....J!^.Lc^^ 187^ ;^




itized by Google



I'M



^ 7 ^ • '■)



Digitized



by Google



Digitized



by Google



Digitized



by Google



i



Digitized



by Google



THE
LONDON, EDINBURGH, and DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.



CONDUCTED BY

SIR ROBERT KANE, LL.D. F.R.S. M.R.I.A. F.C.S.
AUGUSTUS MATTHIESSEN, Ph.D. F.R.S. F.C.S.

AND

WILLIAM FRANCIS, Ph.D. F.L.S. F.R.A.S. F.C.S.



'* Nec aranearum sane textus ideo mefior quia ex se fiia gignunt, nee nosier
vilior quia ex alienis Ubamus at apes." Just. Lips. Polit, lib. i. cap. L Not.



VOL. XXXVII.— FOURTH SERIES.
JANUARY— JUNE 1869.



LONDON.

TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET,
Printers and Publishers to the University of London ;

SOLD BY LONGMANS, GREEN, READER, AND DYER; SIMPKIN, MARSHALL AND CO. ;

WHITTAKER AND CO.; AND KENT AND CO., LONDON*. — BY ADAM AND

CHARLES BLACK, AND THOMAS CLARK, EDINBURGH;

SMITH AND SON, GLASGOW; HODGES AND

SMITH, DUBLIN ; AND PUTNAM,

NEW YORK.



Digitized



by Google



^, 3 7



" Meditationis est perscrutari occulta; contemplationis est admirari

perspicua Admiratio generat qusstionem, qusestio inTestigationenii

inyestigatio inventionem." — Hugo de S, Victore.



— ** Cur Spirent venti, cur terra dehiscat,
Cur mare turgescat, pelago cur tantus amaror.
Cur caput obscura Phcebus ferrugine condat.
Quid toties diros cogat flagrare cometas;
Quid pariat nubes, veniant cur fulmina coelo,
Quo micet igne Iris, superos quis conciat orbes
Tarn yario motu."

J. B, Pinelli ad Mazonium,



Digitized



by Google



CONTENTS OF VOL. XXXVII.

(FOURTH SERIES.)



NUMBER CCXLVI.— JANUARY 1869.

Page

Prof. R. Bunsen on the Washing of Precipitates* (With a Plate.) 1

Mr. F. A. Paget on a New Form of Permanent Magnet 18

Messrs. E. T. Chapman and M. H. Smith on the Action of De-
hydrating Agents on Organic Bodies 20

M. O. E. Meyer on the Explanation of Stewart and Tait's Ex-
periments on the Heating of a Disk rotating in a Vacuum . . 26
Mr. S. Newcomb on Hansen's Theory of the Physical Consti-
tution of the Moon 32

Mr. R. Edmonds on Extraordinary Agitations of the Sea not

produced by Winds or Tides 35

Prof. E. Edlund's Experimental Proof that the Electric Spark is

an Electromotor 41

Mr. H. Wilde on a Property of the Magneto-electric Current to
control and render Synchronous the Rotations of the Arma-
tures of a number of Electromagnetic Induction Machines . . 54
Notices respecting New Books : —

Mr. G. Fownes's Manual of Elementary Chemistry, The-
oretical and Practical 62

Dr. F. Guthrie's Elements of Heat and of Non-metallic
Chemistry. Especially designed for Candidates for the
Matriculation Pass Examination of the University of

London ^ 65

Proceedings of the Royal Society : —

Mr. B. Stewart's Account of certain Experiments on Ane-
roid Barometers, made at Kew Observatory 65

Mr. R. J. Wright on an Easy Method of measuring ap-
proximately the Intensity of Total Daylight 74

On the Dispersive Power of Gases and Vapours, by M. Croul-

lebois 75

On the Generation of Ozone in Oxygen and in Air under the
influence of the condensed Electrical Spark, by MM. L'Hote

and St.-Edme 79

On a New Method of Estimating minute traces of Metals, spe-
cially designed for Water-analysis, by J. Alfred Wanklyn
and Ernest Theophron Chapman 80



Digitized



by Google



IV CONTENTS OP VOL. XXXVII. — FOURTH SERIES.

NUMBER CCXLVII.— FEBRUARY.

Page

M. Dumas*s Remarks on Affinity 81

Messrs. B. Stewart and P. G. Tait on the Heating of a Disk

by rapid rotation in vacuo 97

Prof. W. A. Norton on the Fundamental Principles of Molecular

Physics 98

M. H. St.-Claire Deville on the Temperature of Flames, and its

relations with the Pressure Ill

Prof. J. A. Wanklyn on Ethylate of Sodium and Ethylate of Po-
tassium. — Part. 1 117

Mr. T. Graham on the Relation of Hydrogen to Palladium . . 1 22
Prof. J. LeConte on some Phenomena of Binocular Vision .... 131
Notices respecting New Books: — Mr. J. N. Lockyer's Elemen-
tary Lessons in Astronomy 141

Proceedings of the Royal Society : —

Lieut. J. Herschel on the Lightning Spectrum 142

Mr. J. N. Lockyer on the Spectrum ofa Solar Prominence;

and Spectroscopic Observations of the Sun 143, 144

Proceedings of the Geological Society : —

Dr. J. Schmidt on the Eruption of the Kaimeni of Santorin. 145
Mr. J. Prestwich on the Structure of the Crag-beds of Nor-
folk and Suffolk 146

Mr. J. Thomson on some Genera of Carboniferous Corals. 148
Mr. S. V. Wood, Jun., on the Pebble-beds of Middlesex,

Essex, and Herts 148

Mr. W. Topley on the Cretaceous Rocks of the Bas-Bou-

lonnais 149

Mr. C. H. Weston on the Mendip Anticlinal 150

Mr. R. B. Foote on the Distribution of Stone Implements

in Southern India 150

Mr. G. V. Du Noyer on worked Flint Flakes from Carrick-

fergus and Larne 152

Mr. A. Murray on the Diminution in the Volume of the

Sea during past Geological Epochs 152

Messrs. A. L. Adams and G. Busk : Has the Asiatic Ele-
phant been found in a Fossil State 152

Sir Philip de M. Grey Egerton on the Characters of some

new fossil Fish from the Lias of Lyme Regis 152

Capt. T. Baker on the Geology of Port Santa Cruz 153

Dr. F. Stoliczka on the Jurassic Deposits in the N.W.

Himalaya ^ 153

Mr. J. W. Salter on a true Coal-plant from Sinai 153

Messrs. J. W. Salter and H. Hicks on some Fossils from

the Menevian Group 153

Mr. H. F. Holt on Earthquakes in Northern Formosa . . 154
Mr. A. B. Mitford on the Coal-mines of Iwanai, Island of

Yesso, Japan 1 54

Mr. W. B. Dawkins on a new Species of Fossil Deer from
Clacton, and from the Norwich Crag 154



Digitized



by Google



CONTENTS OP VOL. XXXVII. — FOURTH SERIES. V

Page
Mr. T. Codrington on a section of the Strata from the Chalk

to the Bembridge Limestone at WhiteclifFBay 155

Dr. H. A. Nicholson on the Graptolites of the Coniston

Flags 155

Mr. G. W. Ormerod-on the " Waterstone Beds'* of the

Keuper 155

Mr. £. R. Lnnkester on the remains of Pteraspidian Fishes

in Devonshire and Cornwall 155

Captain James Clark on the Geological peculiarities of the

Saxon Switzerland 156

On the Temperature of Flames and Dissociation, by E. Vicaire. 156

On a Friction and Induction Electrical Machine, by F. Carr6. 160

On the Shape of the Flame of a Bunsen's Burner, by A. Poppe. 160



NUMBER CCXLVIII.—MARCH.

Mr. C. Tomlinson's Historical Notes on some Phenomena con-
nected with the Boiling of Liquids 161

Prof. J. A. Wanklyn on the Compounds of Ethylene-sodium
and of its Homologues 175

Prof. J. Bay ma on the Fundamental Principles of Molecular
Physics 182

Mr. R. Moon on the Theory of Sound 189

Mr. J. CroU on the Physical Cause of the Motion of Glaciers. 201

Mr. R. A. Peacock on Mr. J. CroU's paper ** On Geological
Time, and the probable Date of the Glacial and the Upper
Miocene Period " 206

Prof. A. Lielegg's Contributions to the Knowledge of the Spec-
tra of the Flames of Gases containing Carbon 208

Mr. D. Vaughan on the Secular Effects of Tidal Action 216

Mr. J.J. Sylvester on the Story of an Equation in Differences
of the Second Order 225

Proceedings of the Royal Society : —

Mr. W. Crookes on the Measurement of the Luminous In-
tensity of Light 227

Canon Moseley on the Mechanical Possibility of the
Descent of Glaciers by their Weight only 229

Formation of an Artificial Spectrum with one Fraunhofer's
Line, by A. Wiillner 235

On the Quantity of Electricity produced by the Electrophorus
Machine expressed in Absolute Measure, by F. Kohlrausch. . 236

On the Interference of Liquid Waves, by M. Lissajous 240



NUMBER CCXLIX.— APRIL.

Prof. J. Tyndall on Cometary Theory 241

Chevalier W. von Haidinger's Remarks on the Luminous, Ther-
mal, and Acoustic Phenomena attending the Fall of Meteorites. 246



Digitized



by Google



VI CONTENTS OF TOL. XXXVII. — FOURTH SERIES.

Page
Prof. How's Contributions to the Mineralogy of Nova Scotia . . 264

Dr. Paalzow on the Galvanic Resistance of Liquids 271

Prof. J. Bayma on the Fundamental Principles of Molecular

Physics '. 275

M. O. E. Meyer's Further Remarks on the Explanation of
Stewart and Tait's Experiments on the Heating of a Disk

rotating in vacuo 287

Dr. W. Marcet on the Falsetto or Head-Sounds of the Human

Voice 289

M. H. Wild on the Absorption of Light by the Air 293

Notices respecting New Books : — Mr. F. S. Barflfs Introduc-
tion to Scientific Chemistry 304

Proceedings of the Royal Society : —

The Rev. S. Haughton's Notes of a Comparison of the
Granites of Cornwall and Devonshire with those of

Leinster and Mourne 306

Proceedings of the Geological Society : —

Sir R. I. Murchison on the Geological Structure of North-
western Siberia 309

Prof. Sandberger on a Section of a Well at Kissingen .... 309
Mr. A. Tylor on the Formation of Deltas ; and on the Evi-
dence and Cause of great Changes in the Sea-Level

during the Glacial Period 310

On the Coloration of Peroxide of Nitrogen, by M. Salet .... 312
On the Magnetism of Chemical Compounds, by Professor Wiede-
mann 314

On the Latent Heat of Volatilization of Sal-ammoniac, by M.
C. Marignac 318



NUMBER CCL.— MAY.

Mr. D. Forbes's Researches in British Mineralogy 321

Prof, R. Ball's Lecture Experiments to illustrate the Laws of

Motion 332

Mr. J. C. Douglas on Shadow Optometers 340

Mr. W. Baker on the Cause of a Pink Colour in White-Lead

Corrosions 344

M. L. Soret on the Colour of the Lake of Geneva 345

Prof. J. Bayma on the Fundamental Principles of Molecular

Physics 348

Prof. J. A. Wanklyn on some Reactions of Hydrated Oxide of

Ethylene- sodium 358

Canon Moseley on the Mechanical Impossibility of the De-
scent of Glaciers by their Weight only 363

Canon Moseley on the Uniform Motion of an Imperfect Fluid. 370



Digitized



by Google



CONTENTS OF VOL. XXXVII. FOURTH SERIES. VU

Page
Mr. J. J. Sylvester's Note on a new Continued Fraction appli-
cable to the Quadrature of the Circle 373

Mr. J. J. Sylvester on two remarkable Resultants arising out

of the Theory of Rectifiable Compound Logarithmic Waves. 375
Notices respecting New Books : —

Mr. R. A. Peacock's Physical and Historical Evidences of
vast Sinkings of Land on the North and West Coasts of
France, and South-western Coasts of England, within

the Historical Period 382

Mr. R. A. Peacock on Steam as the Motive Power in Earth-
quakes and Volcanoes, and on Cavities in the Earth's

Crust ' 383

Proceedings of the Royal Society : —

Prof. Tyndall on the Blue Colour of the Sky, the Polariza-
tion of Skylight, and on the Polarization of Light by

Cloudy matter generally 384

Proceedings of the Royal Institution : —

Dr. A. Crum Brown on Chemical Constitution, and its
Relation to Physical and Physiological Properties .... 395
On a Mirage in the English Channel, by John Parnell, M.A.,

F.R.A.S 400

On the production of a beautiful Patina onBronzes in large Towns. 401
On Tyndall's Cometary Theory, by Mr. E. Carpmael and W. B.
Gibbs. F.R.A.S 403. 404



NUMBER CCLL—JUNE.

M. A. WiiUner on the Spectra of certain Gases in Geissler's
Tubes 405

Mr. J. Dewar on the Motion of a Palladium Plate during the
Formation of Graham's Hydrogenium 424

Prof. J. Bayma on the Fundamental Principles of Molecular
Physics 431

Prof. W. Swan on a Metallic Connector to replace the Vulca-
nite Tube used with Bianchi's Air-pump 442

Prof. R. Clausius upon the new Conception of Electrodynamic
Phenomena suggested by Gauss 445

Mr. W. Huggins on some Spectrum Observations of Comets. . 456

Dr, E. J. Mills on Statical and Dynamical Ideas in Chemistry.
— Part I. Acid, Alkali, Salt, and Base 461

Proceedings of the Royal Society : —

Mr. F. Guthrie on the Thermal Resistance of Liquids . . 468
Mr. G. Gore on Hydrofluoric Acid 470

On the Voltaic Deportment of Palladium, by J. C. Poggendorflf. 474



Digitized



by Google



Vlll CONTENTS OF VOL. XXXVII. FOURTH SERIES.

Page
On the Electrical Polarity and Inequality of the Amalgamated

Zinc Electrodes in Sulphate of Zinc, by E. Patry 475

On a Development of Heat which accompanies the bursting of

the Prince Rupert's Drops, by M. Dufour 478

Index 481



PLATE.

Illustrative of Prof. R. Bunsen's Paper on the Washing of Precipitates.



Digitized



by Google



THE
LONDON, EDINBURGH, and DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.



[FOURTH SERIES.]



JANUARY 1869.



I. On the Washing of Precipitates, By R. Bunsbn*.

[With a Plate.]

A PRECIPITATE is washed either by filtration or by decan-
tation : in the former case the portion of liqaid not mecha-
nically retained is allowed to drain from the precipitate ; in the
latter it is separated by simply pouring it away^ the foreign sub-
stances contained in the precipitate being then removed by the
repeated addition of some washing-fluid^ in each successive por-
tion of which the pre ipitate is^ as far as possible^ uniformly sus-
pended^ this process being continued until the amount of im-
purity becomes so minute that its presence may be entirely
disregarded.

Supposing V to represent the volume of the moist precipitate
remaining at the bottom of the vessel after decantation, or upon
the filtrate after filtration, V the volume of wash-water employed
at each successive decantation, n the number of decantations, and

- the fraction expressing the proportion of the original amount

of impurity still remaining in the precipitate after n decantations^
then



\v-¥V "a



(1)

Calling W the total volume of wash-water resulting from n de-

* Translated from the Ann. der Chem. und Pharm. vol, cxlviii. [3], by
Mr. T. £. Thorpe, from the proof-sheets kindly furnished by the Author.

Phil. Mag. S. 4. Vol 37. No. 246. Jan. 1869. B



Digitized



by Google



2 Prof. R. Bunseii on the Washing of Precipitates.

cantatioDs^ then



therefore



nV=W; (2)






or



If we differentiate W with respect to n and make the differential
quotient equal to 0, then the minimum value of W becomes,
when n= 00,

W=:t?nat. log. fl (4)

Precipitates obtained in the course of chemical analysis may
in all cases be assumed to be sufficiently washed when the im-
purity retained by them amounts to no more than the J^ ^
part. Making therefore a =100000 and v = l, it results from
equation (4) that the least quantity of fluid required in order to
remove the impurity contained in a precipitate to the 1
part, amounts to eleven and a half times the volume occupied by
the precipitate itaelf in the liquid in which it exists. It is evi-
dent, therefore, that the amount of water actually necessary to
wash a precipitate the more nearly approaches this minimum the
oftener we decant, and the smaller the quantity of washing- water
^ye employ at each decantation.

Since some of the principal sources of error in analytical work
consist in the incomplete or in the too protracted washing of
precipitates, it becomes important to know how to ascertain the
progress of the washing throughout the several stages of the
process. By employing the same volume of water at each suc-
cessive addition, and estimating its relation to that of the preci-
pitate remaining at the bottom of the vessel or upon the filter,
we can find from the following Table, calculated by means of the
formula above given, the number of times it is necessary to de-
cant in order to diminish the amount of impurity in the precipi-
tate to the ,^^j-^^ - T^rW^r, FTTT^T^} or ,^I^^ part. Column I.

100000* 50000^ 20000* 10000 ^

shows the relation between the volume of the precipitate and that
of the washing-water employed for each successive decantation,
column II. the number of decantations required to diminish the
anu)unt of impurity to the necessary extent, and column III. the
total volume of water obtained from the several decantations.



L_^



Digitized



by Google



Prof. R. Bun sen on the Waahmg af Prec^taies.





1


0'


1

50000*




1


\'


1
10000'


10000


2000<J


I.


II.


III.


I.


II.


III.


I.


II.


III.


I.


II.


III.


V


n.


W.


V


n.


W.


V


n.


W.


V


n.


W.


V






V






V

0-5


244




V






0-5


28-4


14-2


0-5


267


13-3


12-2


0-5


227


114


1


16-6


16-6


I


156


15-6


1


14-3


14-3


1


13-3


18^3


2


10-6


210


2


98


19-7


2


90


180


2


8-4


16-8


3


8-3


24-9


3


7-8


234


3


71


21-4


3


6-6


19-9


4


71


28-6


4


67


26 9


4


61


24-6


4


57


22-9


5


64


321


5


60


30-2


5


5-5


27-6


5


61


257


6


5-9


35-5


6


5-6


33-4


6


5 1


30*5


6


47


28-4


7


6-5


38-8


7


5-2


36-4


7


4-8


33-3


7


4-4


31-0


8


5-2


42


8


4-9


39-4


8


4-5


361


8


4-2


33-5


9


50


450


9


4-7


423


9


4-3


387


9


40


360


10


4-8


480


10


45


451


10


41


41-3


10


3-8


38-4


11


46


51-0


11


4-4


47-9


11


40


43 8


11


37


408


12


4-5


539


12


42


50-6


12


3-9


46-3


12


3-6


431


13


4-4


564


13


41


53-3


13


38


48-8


13


3-5


45-4


14


4-2


59-4


14


40


55-8


14


37


511


14


3-4


47-6


15


4-2


62-3


15


3-9


58-5


15


3-6


53-6


15


3-3


49-8


16


41


650


16


38


611


16


35


560


16


3-3


530


17


4


67-8


17


37


63-6


17


3-4


583


17


3-2


54-2


18


3-9


70-4


18


37


6f51


18


34


60-5


18


31


56-3


19


3-8


74-3


19


3-6


68-6


19


3-3


62 8


19


31


58-4



When the washing-process is performed in a beaker, the rela-
tion between the volume of the precipitate and that of the liquid
may be easily determined by holding a strip of paper along the
side of the vessel and marking upon it the respective heights of
the precipitate and supernatant liquid; then on folding the por-
tion of paper lying between the two marks in such a manner that
each fold corresponds to the height occupied by the precipitate,
the number of folds will give the argument in column I. to
find in column II. the number of decantations needed to wash
to the required extent. If the washing be conducted as in
the ordinary method of filtration, funnels possessing an angle
of 60° must be invariably employed, and the capacities of the
various-sized filters once for all determined by means of a bu-
rette. After the precipitate has been brought upon the filter
and allowed to drain, it is mixed as thoroughly as possible
with water from a graduated washing-flask. Call the amount of
water thus necessary to fill the filter t?, and the capacity of the

empty filter 2?, then ^_ = — in column I.; that is, the argu-
ment needed to find in column II. the number of times it is ne-
cessary to refill the filter in order to wash the precipitate to the
desired extent.

B2



Digitized



by Google



4 Prof. B. Bonsen an the Washing of Precipitates.

I by far prefer using this Table to employing the method ge-
nerally followed of ascertaining the completion of the washing-
process by evaporating a quantity of the filtrate on platinum- foil,
. since in the latter case it is only possible to obtain an infallible
proof when we have to deal with a precipitate possessing an ex-
tremely high degree of insolubility ; if the precipitate be soluble
to any marked extent, the result is completely illusory.

In the process of filtration as hitherto conducted, the time
required is so long and the quantity of wash- water needed so
great that some simplification of this continually recurring ope-
ration is in the highest degree desirable. The following method,
which depends, not upon the removal of the impurity by simple
attenuation, but upon its displacement by forcing the wash-
water through the precipitate, appears to me to combine all the
requisite conditions and therefore to satisfy the need.

The rapidity with which a liquid filters depends, c€Bteris paribus,
upon the difierence which exists between the pressure upon its
upper and lower surfaces. Supposing the filter to consist of a
solid substance, the pores of which suffer no alteration by pres-
sure or by any other influence, then the volume of liquid filtered
in the unit of time is nearly proportional to the difference in
pressure : this is clearly shown by the following experiments,
made with pure water and a filter consisting of a thin plate of
artificial pumice-stone. The thin plate of pumice was hermeti-
cally fastened into a funnel consisting of a graduated cylindrical
glass vessel, the lower end of which was connected with a large
thick flask by means of a tightly fitting caoutchouc cork. The
pressure in the flask was then reduced by rarefying the air by
means of a method to be described upon another occasion ; and
for each difference of pressure p, measured by a mercury column,
the number of seconds / was observed which a given quantity of
water occupied in passing through the filter. The following are
the results : —

I.



P'


t.


pt.


metre.


II




0179


91-7


16-4


0-190


810


15-4


0-282


52-9


14-9


0-472


330


15-6



In the ordinary process of filtration, p on the average amounts
to no more than 0*004 to 0*008 metre. The advantage gained,
therefore, is easily perceived when we can succeed by some
simple practicable and easily attainable method in multiplying



Online LibraryPestalozzianum Zürich Archivbureau der Schweizerischen permanenten SchulPhilosophical magazine → online text (page 1 of 52)