Vol.. XX[V. No. 7.] 
POPULAR SCIENCE NEWS. 
109 
other magnet, and the point of the knife becomes a 
pole of the opposite kind — called north in France 
and south in this country. 
Very truly yours, 
Marcia a. Keith. 
Mount Holyoke Seminary and College, South 
Hadley, Mass., May 10, 1S90. 
Editor of Popular Science News: 
The answer given to the question, "How long 
can a solar eclipse remain total.'" as published in 
the June number of the Science J>Jews, is erro- 
neous. It is possible, at the equator, for totality 
of a solar eclipse to last 7m. 58s. A person, how- 
ever, moving eastward on a rapidly-moving train 
during totality could prolong it to Sm. 
Lewis Swift. 
Warner Observatory, Rochester, N. Y. 
QUESTIONS AND ANSWERS. 
Letters of inquiry should enclose a two-cent 
stamp, as well as the name and address of the 
writer, which will not be published. 
Questions regarding the treatment of diseases 
cannot be answered in this column. 
H. C. W., Mass. — In the common copper-zinc cell, 
where the zinc is amalgamated with mercury, why 
does it not become a mercury-copper cell .' Also, in 
the Callan battery, where one pole consists of iron 
immersed in strong nitric acid, why is it not dis- 
solvtxl.' 
Answtr. — (1) The chemical alTinily between zinc 
and sulphuric acid is much greater than between 
mercury and the acid. Therefore the chemical 
action, upon which the generation of electricity 
depends, will only aflect the zinc as long as any 
remains undissolved. (2) When iron is immersed 
ill strong nitric acid, it enters into a peculiar condi- 
tion known as the passive state, in which it is quite 
insoluble even in weaker acid. The ciiuse of this 
plienomenoii is not fully understood, but it is proba- 
bly due to the formation of a protecting coating 
o) insoluble oxide of iron. 
N. J. 15 , Chicago. — What is the strongest electric 
current that a man can endure without injury.' 
Ansver. — The strength of an electric current 
which the human body can tolerate is extremely 
variable, with different persons and under different 
conditions, and it is impossible to set any definite 
limit. We know of a case where a person received 
a current of 2,000 volts, at first without apparent 
injury, although the after effects were very serious. 
We doubt if this strength has ever been exceeded, 
and in 99 cases out of 100 the current would have 
caused instant death. 
1'. S. M., New York. — Does an electric current 
pass on the surface of a conductor, or through the 
entire mass.' and will a tube convey more electricity 
than a solid rod of the same size.' 
Answer. — A current of electricity passes through 
the entire mass of the conductor. That is, the con- 
ducting power (resistance) of any body is propor- 
tional to the weight of similar lengths. Consequently, 
a solid rod will convey more current than a tube ■ I 
the same diameter. Static electricity, on the con- 
trary, remains upon the surface of the charged 
body, as long as it is not in motion. 
W. S. T., New York. — The tarnishing af your 
watch-case is, undoubtedly, due to the sulphur con- 
tained in the rubber. A pocket of oiled silk or 
some similar impervious substance may remedy the 
trouble. 
B. S. P., Vermont. — Among the other valuable 
properties of platinum is its comparatively small 
toellicient of expansion when heated, which approx- 
imates to that of glass, so that platinum wires can 
be fused into glass — as in electric lamps, Geissler's 
tubes, etc. — without danger of subsequent cracking 
of the glass from unequal expansion. 
Student, Maine. — We should strongly advise 
you to have nothing to do with chloride of nitro- 
gen. It is an extremely dangerous substance to 
work with, and liable to explode at any moment 
with terrific force. Even the most experienced 
chemists have not always escaped unharmed. 
J. M. M., Venn. — Does the microscope reveal any 
difference between human blood and that of domes- 
tic quadrupeds, and does the domestication of wild 
animals alter the condition of the blood-corpuscles? 
Answer. — There is quite a noticeable difference in 
the size of the blood-corpuscles of different animals, 
including man. As far as we know, domestication 
causes no change, either of size or shape. 
LITERARY NOTES. 
The Fairyland of Flowers, by Mara L. Pratt. Edu- 
cational Publishing Co., Boston. Price, $1.00. 
This charming book on botany for young people 
is a popular illustrated botany for home and school. 
In her work, Miss Pratt has endeavored to do some- 
thing more than give mere analytical tables and 
descriptions of species. She has tried to relieve 
the inevitable dryness of a strictly botanical work 
by mingling with her text some of the legends 
of flowers, and here and there a story or a poem 
bearing upon her subject, and all of this she has 
done wonderfully well. Many a young reader will 
be led by this book to almost unconsciously know- 
something of botany, who would turn with weari- 
ness from the average text-book on the subject. In 
the physiological part of her work. Miss Pratt has 
treated the subject easily, presenting what is abso- 
lutely essential to know in a simple manner, and 
leaving the rest to the larger text-books and later 
years of Uie student. This same simplicity of treat- 
ment is to be found in what is more essentially 
technical, the " Flora," which takes the last ninety 
pages of the book. Here, the young reader is led 
by simple analysis to the name of the species on 
which he may be working. The book is a quarto, 
beautifully printed and profusely illustrated, and 
will undoubtedly find ready acceptance with the 
young people. 
The third volume of the magnificent Century 
IMctionary, including the letter L, is now ready. 
As the successive voliunes of this work appear, we 
are more and more impressed with the completeness, 
thoroughness and reliability with which it is edited. 
We notice that scientific terms — a very weak point 
in most dictionaries — are defined and explained 
with the utmost correctness and precision. Taken 
altogether, the work is a great credit to American 
scholarship. 
The Master of the Magicians, by Elizabeth Stuart 
Phelps and Herbert D. Ward. Published by 
Houghton, Mifflin & Co., Boston. 
The extraordinary success of Jien-llur has stimu- 
lated the production of what may be described as the 
religious historical novel, and this present work can 
be recommended as one of the best and most inter- 
esting of its class. The names of the authors are a 
sufficient guarantee of its high value from a literary 
point of view; and, treating as it does of the times 
of the prophet Daniel and the ancient Chaldean 
empire, it is of additional interest as a popular 
archieological work, describing the manners and 
customs of those almost pre-historic times. 
The Report of the Royal Commission vpon the 
Mineral Resources of Ontario has been received, and 
is of interest as showing the variety and number 
of deposits of valuable minerals and metals existing 
in the territory of our northern neighbor. There 
... evidently much mineral wealth in that region 
awaiting proper development. 
Special mention should be made of the receipt 
of the Publications of the Lick Observatory and the 
.Astronomical Society of the Pacific. The latter pub- 
lication contains full reports of the work accom- 
plished at the Lick Observatory', and is furnished 
free to members of the Society. The membership 
dues are five dollars per year, and application may 
be made to the Secretary at 40S California Street, 
San Francisco. 
Pamphlets, etc., received : Grundlagen der Che- 
mie, by D. Mendelejeff, of the University of St. 
Petersburg; Catalogue of Minerals, by George L. 
English & Co., Philadelphia; Tuberculosis in Its 
Relations to Agriculture and Public Health, issued by 
the Massachusetts State Cattle Commission; Elec- 
trolysis in the Treatment of Stricture of the Rectum, 
by Robert Newman, M. D., New York; Report 
of the Brooklyn Health Exhibition, and the Quar- 
terly Report of the U. S. Bureau of Statistics. 
n^ediciRc aijd Pliariijacy. 
VITALITY. 
The greatest of all mysteries is that of the 
true nature of Life, or tlie principle of vital- 
ity. Without going into abstruse philosophi- 
cal reasonings, the fact of the actual existence 
of life must be an admitted fact, even if the 
question of the subjectivity or objectivity 
of what we call matter and energy is left 
undecided. The writer, or the reader of these 
lines must necessaril}' be sure of his own 
existence — that is, the existence of jierceptive 
faculties, although the certainty ol" the actual 
existence of anything else ma}' be unprova- 
ble. We are unable to separate our intelli- 
gence from ourselves ; and, although it is a 
fanciful, and perhaps illogical speculation, yet 
the idea that all the surrotmding universe has 
no real existence, but is only the "baseless 
fabric of a vision," and that / — the ci^o — am 
the universe, must have occurred, at times, to 
every thoughtful person. 
Practically, however, we mu.st base oin- 
actions upon the existence of an outside 
world, and the more we can bring ourselves 
into harmony with the conditions which 
en\iron us, the greater happiness and satis- 
faction we shall obtain. Pain and pleasure 
are realities ; and to avoid the one and attain 
the other in the highest degree is the "chief 
end of man" — actually, at least, notwith- 
standing the doctrines of the "shorter Cat- 
echism." 
A newly-laid egg is, apjjarently, nothing 
but a mass of albumen, with a few other 
complex organic chemical compounds ; but 
the miraculous changes which occur when 
it is submitted to a gentle heat for a few 
weeks, show that this mass of albumen is 
wonderfully different from the simple organic 
substance known by that name. The little 
microscopical cell, or germinal vesicle, in the 
yolk possesses the power of setting up a 
rearrangement of the molecides of the 
material of the egg, which results in the 
formation of such complicated substances as 
are represented by feathers, bones, skin, 
flesh, etc., and, as a whole, endowed with 
the power of voluntary motion, of obtaining 
and assimilating other material into its struc- 
ture, and, — most wonderful of all, — in due 
time, of producing other eggs endowed with 
the same remarkable properties, and thus 
preserving and transmitting the principle 
of vitality for an unlimited period. 
If, on the other hand, we destroy or remove 
the germinal vesicle before submitting the 
egg to heat and moisture, what a diflerent set 
of chemical reactions occur. It is like a 
clock from which the escapement has been 
removed. The complex molecules of the 
albumen and other compounds tumble down 
like a house of cards, the sulphur unites with 
hydrogen, — forming the familiar and offensive 
