Transcriber’s note: Table of Contents added by Transcriber.
CONTENTS
Chapters on the Stars 227
Preventive Inoculation. (II.) 240
Colonies and the Mother Country. (II.) 248
Technical Education at the Massachusetts Institute of
Technology 257
The Psychology of Crazes 285
Some Phases of the Earth’s Development in the Light of Recent
Chemical Research 295
A Preliminary Account of the Solar Eclipse of May 28, 1900,
As Observed by the Smithsonian Expedition 302
Malaria and the Malarial Parasite 310
New Sources of Light and of Röntgen Rays 318
Discussion and Correspondence 323
Scientific Literature 327
The Progress of Science 332
THE
POPULAR SCIENCE
MONTHLY
EDITED BY
J. McKEEN CATTELL
VOL. LVII
MAY TO OCTOBER, 1900
NEW YORK AND LONDON
McCLURE, PHILLIPS AND COMPANY
1900
COPYRIGHT, 1900,
BY McCLURE, PHILLIPS AND COMPANY.
[Illustration: PRESIDENT G. K. GILBERT,
AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE.]
THE
POPULAR SCIENCE
MONTHLY.
JULY, 1900.
CHAPTERS ON THE STARS.
BY PROFESSOR SIMON NEWCOMB.
I. INTRODUCTORY.
It would be difficult to name any subject of investigation, the
progress of which during our time has been more remarkable than that in
the field of stellar astronomy. Several features of this progress are
especially noteworthy. One of these is the mere extension of research.
A natural result of the northern hemisphere being the home of civilized
peoples was that, thirty years ago, the study of the southern heavens
had been comparatively neglected. It is true that the curiosity of
the inquiring astronomers of the past would not be satisfied without
their knowing something of what was to be seen south of the equator.
Various enterprises and establishments had therefore contributed to
our knowledge of the region in question. As far back as 1667, during
a voyage to St. Helena, Halley catalogued the brighter stars in the
region near the South Pole. About 1750 Lacaille, of France, established
an observing station at the Cape of Good Hope, and made a catalogue
of several thousand stars which has remained a handy book for the
astronomer up to the present time. In 1834-38 Sir John Herschel made a
special voyage to the Cape of Good Hope, armed with the best telescopes
which the genius of his father had shown him how to construct, for
the purpose of doing for the southern heavens as much as possible of
what his father had done for the northern. The work of this expedition
forms one of the most important and interesting chapters in the history
of astronomic science. Not only is Herschel’s magnificent volume a
classic of astronomy, but the observations which it contains are still
as carefully and profitably studied as any that have since been made.
They may be said to form the basis of our present knowledge of the
region which they included in their scope.
Herschel’s work may be described as principally in the nature of
an exploration. He had no instruments for accurately determining
the positions of stars. In the latter field the first important
contributions after Lacaille were made by Sir Thomas Brisbane, Governor
of New South Wales, and Rumker, his assistant, at Paramata. Johnson, of
England, about 1830, introduced modern accuracy into the construction
of a rather limited catalogue of stars which he observed at St.
Helena. About the same time the British Government established the
observatory at the Cape of Good Hope, which has maintained its activity
to the present time, though, at first, its means were extremely
limited. About the middle of the century the Government of New South
Wales established, first at Williamstown and then at Melbourne, an
observatory which has worked in the same field with marked success.
An American enterprise in the same direction was that of Captain James
M. Gilliss, who, in 1849, organized an astronomical expedition to
Chili. The principal motive of this enterprise was the determining of
the solar parallax by observations upon Venus and Mars near the time
of their nearest approach to the earth. As these observations would
take but a small part of his time, Gilliss determined to take with him
instruments for determining the positions of the stars. He established
his observatory at a point near Santiago, where he continued his
observations for nearly three years. He was a practical observer,
but an untoward circumstance detracted from the value of his work.
His observatory was built upon a rocky eminence, a foundation which
seemed to afford the best possible guarantee of the stability of his
instruments. He made no attempt to reduce his observations till after
his return home. Then it was found that the foundation, through the
expansion and contraction due to the heat of the sun, was subject to a
diurnal change which made it extremely difficult to derive good results
from his careful work. It was not until 1896, more than thirty years
after his death, that the catalogue of the stars observed by him was at
last completed and published.
We do not derogate in any way from the merit of these efforts in saying
that they could not lead to results comparable with those of the score
of richly equipped northern observatories which the leading nations
and universities of Europe had endowed and supported for more than a
hundred years. Only within the last thirty years has it been possible
to bring our knowledge of the southern heavens up to a satisfactory
stage. Now, however, the progress of southern astronomy, if we may use
the term, is such that in several points our knowledge of the southern
heavens surpasses that of the northern ones. If we measure institutions
by the importance of the work they are doing, there are several in the
southern hemisphere which must to-day be placed in the first rank.
The history and work of the Cordova Observatory are of special
interest. In 1870 Dr. B. A. Gould, who might fairly be considered
as the father of modern American astronomy, conceived the idea of
establishing an observatory of the first class in South America. He
found the President and Governor of the Argentine Republic ready to
support his scheme with a liberality well fitted to impress us with
a high sense of their standard of civilization. In a year or two the
observatory at Cordova was in active operation. A statement of its work
belongs to a subsequent chapter. Suffice it to remark here that Dr.
Gould continued in active charge until 1885, when he returned home, and
was succeeded by Thome, the present director.
A few years after Gould went to Cordova, Gill was made director of the
Royal Observatory at the Cape of Good Hope. The rapid growth of this
institution to one of the first rank is due no less to the scientific
ability of the new director than to the unflagging energy which he has
devoted to the enlargement of the resources of the institution. The
great fact which he sought to impress upon his supporters was that
the southern celestial hemisphere was as large as the northern, and
therefore equally worthy of study.
In any general review of the progress of stellar astronomy during the
past twenty years, we should find Harvard University before us at every
turn. What it has done will be seen, perhaps in an imperfect way, in
subsequent chapters. Not satisfied with the northern hemisphere, it
has established a branch at Arequipa, Peru, in which its methods of
observation and research are extended to the south celestial pole.
Its principal specialties have been the continuous exploration of the
heavens. Celestial photography, photometry and spectroscopy sum up its
fields of activity. For more than ten years it might be almost said
that a sleepless watch of the heavens has been kept up by an all-seeing
photographic eye, with an accuracy of which the world has hardly had
a conception. The completeness with which its work has been done has
recently been shown in a striking way. Our readers are doubtless
acquainted with the singular character of the minor planet Eros, whose
orbit passes through that of Mars, as one link of a chain passes
through another, and which comes nearer the earth at certain times than
any other celestial body, the moon excepted. When the character of
the orbit became established, it was of interest to know whether the
planet had ever been observed as a fixed star at former oppositions.
Chandler, having computed the path of the planet at the most important
of the oppositions, beginning with 1892-94, communicated his results to
Director Pickering, and suggested a search of the Harvard photographs
to see if the planet could be found on them. The result was the
discovery of the planet upon more than a score of plates taken at
various times during the preceding ten years. New stars were formerly
supposed to be of very rare occurrence, but since the Harvard system of
photographing the heavens has been introduced, no less than three have
been known to break out.
The great revelations of our times have come through the application
of the spectroscope to the measurement of motions in the line of sight
from us to a star. No achievement of the intellect of man would have
seemed farther without the range of possibility to the thinker of half
a century ago, than the discoveries of invisible bodies which are now
being made with this instrument. The revelations of the telescope
take us by surprise. But, if we consider what the thinker alluded to
might regard as attainable, they are far surpassed by those of the
spectroscope. The dark bodies, planets, we may call them, which are
revolving round the stars, must be forever invisible in any telescope
that it would be possible to construct. They would remain invisible if
the power of the instrument were increased ten thousand times. And yet,
if there are inhabitants on these planets, our astronomers could tell
them more of the motions of the world on which they live than the human
race knew of the motions of the earth before the time of Copernicus.
The men and institutions which have contributed to this result are
so few in number that it will not be tedious to mention at least the
principal actors. The possibility of measuring the motions of the stars
in the line of sight by means of the spectroscope was first pointed
out by Mr. now Sir William Huggins. He actually put the method into
operation. As soon as its feasibility was demonstrated it was taken up
at Greenwich. In these earlier attempts, eye methods alone were used,
and the results were not always reliable. Then spectrum photography
was applied at the astrophysical observatory at Potsdam by Vogel.
Thence the photographic method soon spread to Meudon and Pulkova.
But, as often happens when new fields of research are opened, we find
them ablaze in quarters where we should least expect. The successful
application of the method requires not only the best spectroscope, but
the most powerful telescope at command. Ten years ago the most powerful
telescope in the world was at the Lick Observatory. Mr. D. O. Mills put
at its eye end the best spectrograph that human art could make at that
time, the work of Brashear. It is Campbell, who, with this instrument,
has inaugurated a series of discoveries in the line in question which
are without a parallel.
A mere survey of what has been done in the various lines we have
mentioned would be far from giving an idea of the real significance of
the advance we are considering. Cataloguing the stars, estimating their
magnitudes, recording and comparing their spectra and determining
their motions, might be considered as, after all, barren of results
of the highest human interest. When we know the exact position of
every star in the heavens, the direction in which it is moving and the
character of its spectral lines, how much wiser are we?
What could hardly have been foreseen fifty years ago, is that these
various classes of results are now made to combine and converge upon
the greatest problem which the mind of man has ever attempted to
grasp--that of the structure of the universe. The study of variable
stars has suddenly fallen into line, so to speak, so that now, it is
uniting itself to the study of all the other subjects to give us at
least a faint conception of what the solution of this problem may be.
One of the principal objects of the present chapter is to make
a comparison of these various researches, and discuss the views
respecting the constitution of the stars individually, as well as of
the universe as a whole, to which they lead us. But there are a number
of details to be considered singly before we can combine results in
this way. Our early chapters will therefore be devoted to the special
features and individual problems of stellar astronomy which have
occupied the minds of astronomers from the beginning of their work to
the present time. Keeping these details in mind, we can profitably
proceed to the consideration of the general conclusions to be drawn
from them.
We may begin by refreshing our memories on some points, an
understanding of which must be taken for granted. What are familiarly
known as the heavenly bodies belong to two classes. Those nearest to us
form a sort of colony far removed from all the others, called the solar
system. The principal bodies of this system are the sun and eight great
planets with their moons, revolving round it. On one of the planets,
small when compared with the great bodies of the universe, but large to
our every-day conceptions, we dwell. The other planets appear to us as
stars. Four of them, Venus, Mars, Jupiter and Saturn, are distinguished
from the fixed stars by their superior brightness and characteristic
motions. Of the remaining three, Mercury will only rarely excite
notice, while Uranus and Neptune are as good as invisible to the naked
eye.
The dimensions of the solar system are vast when compared with any
terrestrial standard. A cannon shot going incessantly at its utmost
speed would be a thousand years in crossing the orbit of Neptune
from side to side. But vast as the dimensions are, they sink into
insignificance when compared with the distance of the stars. Outside
the solar system are spaces which, so far as we know, are absolutely
void, save here and there a comet or a meteor, until we look far
outside the region which a cannon shot would cross in a million of
years.
The nearest star is thousands of times farther away than the most
distant planet. Scattered at these inconceivable distances are the
bodies to which our attention is directed in the present work. If we
are asked what they are, we may reply that the stars are suns. But we
might equally well say that the sun is one of the stars; a small star,
indeed, surrounded by countless others, many of which are much larger
and brighter than itself. We shall treat our theme as far as possible
by what we may call the natural method, beginning with what, being most
obvious to the eye, was first noticed by man, or will be first noticed
by an observer, and tracing knowledge up step by step to its present
state.
Several features of the universe of stars will be evident at a glance.
One of these is the diversity of the apparent brightness, or, in
technical language, of the magnitudes of the stars. A few far outshine
the great mass of their companions. A greater number are of what we may
call medium brightness; there is a yet larger number of fainter ones,
and about one half of all those seen by a keen eye under favorable
conditions are so near the limit of visibility as to escape ordinary
notice. Moreover, those which we see are but an insignificant fraction
of the number revealed by the telescope. The more we increase our
optical power, the greater the number that come into view. How many
millions may exist in the heavens it is scarcely possible even to
guess. The photographic maps of the heavens now being made probably
show fifty millions, perhaps one hundred millions or more.
Another evident feature is the tendency of the brighter stars to
cluster into groups, known as constellations. The latter are extremely
irregular, so that it is impossible to decide where one constellation
should end and another begin, or to which constellation a certain star
may belong. Hence, we can neither define the constellations nor say
what is their number, and the division of the stars among them is a
somewhat arbitrary proceeding.
A third feature is the Milky Way or Galaxy, which, to ordinary vision,
appears as an irregular succession of cloud-like forms spanning the
heavens. We now know that these seeming clouds are really congeries of
stars too small to be individually visible to the naked eye. We shall
hereafter see that the stars of the Galaxy form, so to speak, the base
on which the universe appears to be constructed. Each of these three
features will be considered in its proper place.
II. MAGNITUDES OF THE STARS.
The apparent brightness of a star, as we see it from the earth, depends
upon two causes--its intrinsic brilliancy or the quantity of light
which it actually emits, and its distance from us. It follows that if
all the stars were of equal intrinsic brightness we could determine
their relative distances by measuring the respective amounts of light
which we receive from them. The quantity of light in such a case varies
inversely as the square of the distance. This will be made evident
by Fig. 1, where S represents the position of a star, regarded as a
luminous point, while A and B are screens placed at such a distance
that each will receive the same amount of light from the star. If the
screen B is twice as far as the screen A, its sides must be twice
as large as those of A in order that it shall receive all the light
that would fall on A. In this case its surface will be four times the
surface of A. It is then evident that any small portion of the surface
of B will receive one fourth as much light as an equal portion of
surface A. Thus an eye or a telescope in the position B will receive
from the star one fourth as much light as in the position A, and the
star will seem one fourth as bright.
[Illustration: FIGURE 1.]
The fact is, however, that the stars are very unequal in their actual
brightness, and in consequence the apparent magnitude of a star gives
us no clue to its distance. Among the nearer of the stars are some
scarcely, if at all, visible to the naked eye, while among the brighter
ones are several whose distances are immeasurably great. A remarkable
example is that of Caropes, the second brightest star in the heavens.
For these reasons astronomers are obliged to content themselves, in the
first place, with determinations of the actual amount of light that the
various stars send to us, or their apparent brilliancy, without regard
to their distance or actual brilliancy. The ancient astronomers divided
all the stars they could see into six classes, the number expressing
the apparent brightness being called the magnitude of the star. The
brightest ones, numbering in all about fourteen, were said to be of
the first magnitude. The fifty next in brightness were said to be of
the second magnitude. Three times as many, an order fainter, were of
the third magnitude. The progression was continued up to the sixth
magnitude, which included those which were barely visible.
As the stars are actually of every degree of apparent brilliancy, no
sharp line of demarkation could be drawn between those of one magnitude
and those of the magnitude next higher. Hence, different observers
made different estimates, some calling a star of the second magnitude
which others would call of the first, while others would designate a
star of the third magnitude which others would call of the second. It
is therefore impossible to state with absolute numerical precision what
number of stars should be regarded of one magnitude and what of another.
An idea of the magnitude of a star can be readily gained by the casual
observer. Looking at the heavens on almost any cloudless evening, we
may assume that the two, three or more brightest stars which we see are
of the first magnitude. As examples of those of the second magnitude,
may be taken the five brightest stars of the Dipper, the Pole Star and
the brighter stars of Cassiopeia. Some or all of these objects can
be seen on any clear night of the year in our latitude. Stars of the
third magnitude are so numerous that it is difficult to select any one
for comparison. The brightest star of the Pleiades is really of this
magnitude, but it does not appear so in consequence of the five other
stars by which it is surrounded. At a distance of 15° from the Pole
Star, Beta Ursa Minoris is always visible, and may be distinguished by
being slightly redder than the Pole Star; it lies between two fainter
stars, the brighter of which is of the third and the other of the
fourth magnitude. The five readily visible but fainter stars of the
Pleiades are about of the fourth magnitude. Of the fifth magnitude are
the faintest stars which are easily visible to the naked eye, while the
sixth comprises those which are barely visible with good eyes.
Modern astronomers, while adhering to the general system which has
come down to them from ancient times, have sought to give it greater
definiteness. Careful study showed that the actual amount of light
corresponding to the different magnitudes varied nearly in geometrical
progression from one magnitude to another, a conclusion which accords
with the well-known psychological law that the intensity of sensation
varies by equal amounts when the exciting cause varies in geometrical
progression. It was found that an average star of the fifth magnitude
gave between two and three times as much light as an average one of
the sixth; one of the fourth gave between two and three times as much
light as one of the fifth; and so on to the second. In the case of
the first magnitude, the diversity is so great that it is scarcely
possible to fix an average ratio. Sirius, for example, is really six
times as bright as Altair, which is commonly taken as a standard for
a first magnitude star. To give precision to their estimates, modern
astronomers are gradually seeking to lay the subject of magnitudes on
an exact basis by defining a change of one unit in the magnitude as
corresponding to an increase of about two and one half times in the
amount of light.
If the practice of separating the visible stars into only six orders
of magnitude were continued without change, we should still have
the anomaly of including in one class stars of markedly different
degrees of brightness. Some more than twice as bright as others would
be designated of the same magnitude. Hence, to give quantitative
exactness to the results, a magnitude is regarded as a quantity which
may have any value whatever, and may be expressed by decimals--tenths
or even hundredths. Thus, we may have stars of magnitude 5.0, 5.1,
5.2, etc., or we may even subdivide yet farther and speak of stars
having magnitudes 5.11, 5.12, etc. Unfortunately, however, there
is as yet no way known of determining the amount of light received
from a star except by an estimate of its effect upon the eye. Two
stars are regarded as equal when they appear to the eye of equal
brilliancy. In such a case the judgment is very uncertain. Hence,
observers have endeavored to give greater precision to it by the use
of photometers,--instruments for measuring quantities of light. But
even with this instrument the observer must depend upon an estimated
equality of light as judged by the eye. The light from one star is
increased or diminished in a known proportion until it appears equal to
that of another star, which may be an artificial one produced by the
flame of a candle. The proportion of increase or diminution shows the
difference of magnitude between the two stars.
As we proceed to place the subject of photometric measures of star
light on this precise basis we find the problem to be a complex one.
In the first place not all the rays which come from a star are visible
to our eyes as light. But all the radiance, visible or invisible,
may be absorbed by a dark surface, and will then show its effect by
heating that surface. The most perfect measure of the radiance of a
star would therefore be the amount of heat which it conveys, because
this expresses what is going on in the body better than the amount of
visible light can do. But unfortunately the heating effect of the rays
from a star is far below what can be measured or even indicated by any
known instrument. We are therefore obliged to abandon any thought of
determining the total amount of radiation and confine ourselves to that
portion which we call light.
Here, when we aim at precision, we find that light, as we understand
it, is properly measured only by its effect on the optic nerve, and
there is no way of measuring this effect except by estimation. Thus,
all the photometer can do is to give us the means of increasing or
diminishing the light from one star, so that we can make it equal by
estimation to that from some other star or source of light.
The difficulty of reaching strict results in this way is increased by
the fact that stars are different in color. Two lights can be estimated
as equal with greater precision when they are of the same color than
when their colors are different. An additional source of uncertainty
is brought in by what is known as the Purkinje phenomenon, after the
physicist who first observed it. He found that if we took two lights of
equal apparent brightness, the one red and the other green, and then
increased or diminished them in the same proportion, they would no
longer appear equal. In other words, the geometrical axiom that halves
or quarters of equal quantities are themselves equal, does not apply to
the effect of light on the eye. If we diminish the two equal lights,
we find that the green will look brighter than the red. If we increase
them in the same proportion, the red will look brighter than the green.
In other words, the red light will, to our vision, increase or fade
away more rapidly with a given amount of change than the green light
will.
It is found in recent times that this law of change does not extend
progressively through all spectral colors. It is true that as we pass
from the red to the violet end of the spectrum the yellow fades away
less rapidly with a given diminution than does the red, and the green
still less rapidly than the yellow. But when we pass from the green to
the blue, it is said that the latter does not fade out quite so fast as
the green.
One obvious conclusion from all this is that two stars of different
colors which look equal to the naked eye will not look equal in the
telescope. The red or yellow star will look relatively brighter in a
telescope; the green or bluish one relatively brighter to the naked eye.
In recent times stars have been photographed on a large scale. Their
magnitudes can then be determined by the effect of the light on
the photographic plate, the impression of the star, as seen in a
microscope, being larger and more intense as the star is brighter.
But the magnitude thus determined is not proportional to the apparent
brightness as seen by the eye, because the photographic effect of
blue light is much greater than that of red light having the same
apparent brightness. In fact, the difference is so great that, with
the chemicals formerly used, red light was almost without photographic
effect. Even now, what we measure in taking the photograph of a star
is almost entirely the light in the more refrangible portions of the
spectrum. It appears, therefore, that when a blue and a yellow star,
equally bright to the naked eye, are photographed, the impression made
on the negative by the blue star will be greater than that made by the
yellow one. A distinction is therefore recognized between photographic
and visual magnitudes.
The photographic magnitudes of the stars are now being investigated and
catalogued on a scale even larger than that on which we have studied
the visual magnitudes. Yet we have to admit the non-correspondence
of the two systems. The bluer the star, the brighter will be its
photographic as compared with its visual magnitude. The most that can
be done is to bring about the best attainable agreement between the two
systems in the general average of all the stars.
Fortunately the differences between the colors of the stars are by
no means so great as those between the colors of natural objects
around us. All the stars radiate light of all colors; and although the
difference is quite appreciable either by the eye or by the photograph,
it is not so great as it would have been were the variations in color
as wide as in the case of terrestrial objects.
Two comprehensive surveys of the heavens, intended to determine as
accurately as possible the magnitudes of all the brighter stars, have
recently been undertaken. One of these is the Harvard photometry,
commenced by Professor Pickering at the Harvard Observatory, and
now extended to the Southern Hemisphere by the aid of a branch
establishment at Arequipa, Peru.
The instrument designed by Professor Pickering for his purpose is
termed a meridian photometer, and is so arranged that the observer
can see in the field of his telescope a reflected image of the Pole
Star, and, at the same time, the image of some other star while it is
passing the meridian. By a polarizing apparatus the image of the star
to be measured is made to appear of equal brightness with that of the
Pole Star, and the position of a Nicol prism, which brings out this
equality, shows the ratio between the magnitudes of the two stars.
The other survey, with the same object, is now being made at the
Potsdam Astrophysical Observatory, near Berlin. In the photometer
used by the German astronomers the image of one star is compared
with an artificial star formed by the flame of a candle. The work is
performed in a more elaborate way than at the Harvard Observatory,
and in consequence, only that part of the heavens, extending from the
equator to 40° north declination, has been completed and published.
A comparison of the results thus obtained with those of Professor
Pickering, shows a curious difference depending on the color of the
star. In the case of the reddest stars, the estimates are found to be
in fairly close agreement, Pickering’s being a little the fainter.
But in the case of the white or bluish stars, the estimates of the
German astronomers are more than one fourth of a magnitude greater
than those of Pickering. This corresponds to an increase of nearly one
fifth in the brightness. Whether this difference is to be regarded as
purely psychological or due to the instruments used, is an interesting
question which has not yet been settled. It is difficult to conceive
how different instruments should give results so different. On the
other hand, the comparisons made by the Germans make it difficult to
accept the view that the difference is due purely to the personality
of the observers. There are two German observers, Drs. Müller and
Kempf, whose results agree with each other exactly. On the other hand,
Pritchard, at Oxford, made quite an extensive photometric survey,
using an instrument by which the light of one star was cut down by
a wedge-shaped dark glass, whereby any gradation of light could be
produced. A comparison shows that the results of Pritchard agree
substantially with those of Pickering. It is quite possible that the
Purkinje phenomenon may be the cause of the difference, the source of
which is eminently worthy of investigation.
This fact simply emphasizes the lack of mathematical precision in
photometric measurements of star light. Even apart from this difference
of color, the estimates of two observers will frequently differ by 0.2
and sometimes by even 0.3 of a magnitude. These differences correspond
roughly to 20 or 30 per cent in the amount of light.
It must not be supposed from this that such estimates are of no value
for scientific purposes. Very important conclusions, based on great
numbers of stars, may be drawn even from these uncertain quantities.
Yet, it can hardly be doubted that if the light of a star could be
measured from time to time to its thousandth part, conclusions of yet
greater value and interest might be drawn from the measures.
We have said that in our modern system the aim has been to so designate
the magnitudes of the stars that a series of magnitudes in arithmetical
progression shall correspond to quantities of light ranging in
geometrical progression. We have also said that a change of one unit
of magnitude corresponds to a multiplication or division of the light
by about 2.5. On any scale of magnitude this factor of multiplication
constitutes the light-ratio of the scale. In recent times, after much
discussion of the subject and many comparisons of photometric measures
with estimates made in the old-fashioned way, there is a general
agreement among observers to fix the light ratio at the number whose
logarithm is 0.4. This is such that an increase of five units in the
number expressing the magnitude corresponds to a division of the light
by 100. If, for example, we take a standard star of magnitude one and
another of magnitude six, the first would be 100 times as bright as the
second. This corresponds to a light ratio slightly greater than 2.5.
When this scale is adopted, the series of magnitudes may extend
indefinitely in both directions so that to every apparent brightness
there will be a certain magnitude. For example, if we assign the
magnitude 1.0 to a certain star, taken as a standard, which would
formerly have been called a star of the first magnitude, then a star a
little more than 2.5 times as bright would be of magnitude one less in
number, that is, of magnitude 0. The one next brighter in the series
would be of magnitude -1. So great is the diversity in the brightness
of the stars formerly called of the first magnitude that Sirius is
still brighter than the imaginary star just mentioned, the number
expressing its magnitude being -1.4.
This suggests what we may regard as one of the capital questions in
celestial photometry. There being no limit to the extent of the scale,
what would be the stellar magnitude of the sun as we see it when
expressed this way on the photometric scale? Such a number is readily
derivable when we know the ratio between the light of the sun and that
of a star of known magnitude. Many attempts have been made by observers
to obtain this ratio; but the problem is one of great difficulty, and
the results have been extremely discordant. Amongst them there are
three which seem less liable to error than others; those of Wollaston,
Bond and Zöllner. Their results for the stellar magnitude of the sun
are as follow:
Wollaston -26.6
Bond -25.8
Zöllner -26.6
Of these, Zöllner’s seems to be the best, and may, therefore, in taking
the mean, be entitled to double weight. The result will then be:
Stellar magnitude of sun -26.4
From this number may be readily computed the ratio of sunlight to that
of a star of any given magnitude. We thus find:
The sun gives us:
10,000,000,000, the light of Sirius.
91,000,000,000, the light of a star of magnitude 1.
9,100,000,000,000, the light of one of magnitude 6.
The square roots of these numbers show the number of times we should
increase the actual distance of the sun in order that it might shine
as a star of the corresponding magnitude. These numbers and the
corresponding parallax are as follows:
Sirius; Distance = 100,000: Parallax = 2″.06
Mag. 1 ” 302,000: ” 0″.68
” 2 ” 479,000: ” 0″.43
” 3 ” 759,000: ” 0″.27
” 4 ” 1,202,000: ” 0″.17
” 5 ” 1,906,000: ” 0″.11
” 6 ” 3,020,000: ” 0″.07
These parallaxes are those that the sun would have if placed at such a
distance as to shine with the brightness indicated in the first column.
They are generally larger than those of stars of the corresponding
magnitudes, from which we conclude that the sun is smaller than the
brighter of the stars.
PREVENTIVE INOCULATION. (II.)
BY DR. W. M. HAFFKINE,
DIRECTOR-IN-CHIEF, GOVERNMENT PLAGUE RESEARCH LABORATORY, BOMBAY.
In a previous paper I reviewed briefly the history of preventive
inoculation and described the results of my attempts to secure a ‘virus
fixé’ in the case of cholera. It will be remembered that the two
vaccines finally obtained protected guinea pigs successfully against
all possible forms of cholera infection.
It was now necessary to ascertain whether the same protection could
be given to man which was observed in animals. For this purpose it
was essential to first of all prove the perfect harmlessness of the
operation. This was established by very careful observations of medical
men and scientists who were inoculated in Europe soon after the results
of the above investigations were published. The inoculation causes a
rise of temperature and general discomfort, which lasts one or two
days, and some pain at the seat of the injection, which disappears
in a few days. The fever and discomfort induced are, on the whole,
shorter in duration, though often more intense, than those caused by
vaccination against smallpox. The effect disappears within a few days
and the individual returns to his usual condition of health.
The next and all-important stage was to devise an experiment or a
series of experiments on man so as to test the efficiency of the method
against cholera attacks. This part of the investigation could only be
done in a cholera-stricken country, where opportunities would arise of
comparing the incidence of the disease in inoculated and uninoculated.
Such opportunities are limited. Except in certain parts of India
and China, cholera appears in localities unexpectedly and does not
last long. In the places where the disease is endemic the cases are
scattered over large areas. These features rendered the demonstration
of the effect of the vaccine a matter of particular difficulty. In
1893 I went to India, and in the course of a year inoculated some
twenty-three thousand people in the northern parts of the country;
but no cholera appeared in their midst to show whether the vaccine
was of value or not. In the spring of 1894 the inoculations were
introduced into Bengal, and, with the assistance and co-operation of
Prof. W. J. Simpson, of King’s College, London, at that time Health
Officer of Calcutta, and of his staff, efforts were made to induce the
inhabitants of the _bustees_ of Calcutta to get themselves inoculated.
These bustees are isolated villages consisting of groups of mud huts
inhabited by the poorer class. Owing to the consumption of water from
the ponds or tanks belonging to these villages, the inhabitants of the
bustees are subject to periodic visitations of cholera. It was in one
of these bustees that the first observation was made as to the effect
of the cholera vaccines.
The spring is essentially the cholera season in Calcutta. About the end
of March two fatal cases of cholera and two cases of choleraic diarrhœa
occurred in Katal Bagan Bustee, in a population grouped around two
tanks. This outbreak led to the inoculation of one hundred and sixteen
persons in the bustee out of about two hundred. After the inoculation
there occurred nine more cases of cholera, seven of which proved fatal,
and one case of choleraic diarrhœa. All the ten cases occurred among
the uninoculated portion of the inhabitants, which formed the minority,
none of the inoculated suffering. The results were more interesting
when analyzed in detail. Some of the cases had occurred in families in
which some of the members had been inoculated and others not, and the
disease selected the non-inoculated members, sparing the inoculated.
Thus, in one house six members out of eight had been inoculated. The
attack, a fatal one, occurred in one of the remaining two. In another
house eleven members out of eighteen were inoculated. The eleven
members remained free while four out of seven not inoculated were
attacked.
Upon these observations the Calcutta municipality felt encouraged to
vote funds for the continuance of the inoculations in an experimental
farm, and appointed for that purpose a special staff. In 1896 the
result of two years’ observations were embodied by the health officer
in a report to the Calcutta Municipal Corporation. It recorded a most
satisfactory state of affairs. During the time under observation some
eight thousand persons were inoculated. Cases of cholera occurred
in seventy-seven huts in which some members of the family had been
previously inoculated and others not. Comparing the incidence of the
disease in the two groups, a striking advantage was found to be with
the inoculated. I made an analysis of the cases according to the time
which had elapsed between inoculation in each of these huts and the
occurrence of cholera in them, and the following results were found.
During the first four days after inoculation, apparently before
the vaccine had time to produce its full protective effect, there
were proportionately 1.86 times fewer deaths among the inoculated
than among the non-inoculated members of the families. In a second
period, extending from the fifth to the four hundred and twenty-ninth
day--i. e., for fourteen months--there were 22.62 times fewer deaths
among the inoculated; while in the last period--that is, between the
four hundred and thirtieth and seven hundred and twenty-eighth day
after the inoculation--there were only 1.54 fewer deaths among the
inoculated, the immunity having evidently gradually disappeared. The
net result was that for two years after inoculation, including the
periods of incomplete protection, there was a reduction in mortality
of 72.47 per cent among the inoculated; or in other words, in houses
in which inoculations were performed and in which cholera subsequently
occurred there were, even from the day of inoculation, before the full
effect of it could be produced, eleven deaths among the non-inoculated
to only three among the inoculated. Eight lives out of every eleven
were saved.
At the end of my first cholera campaign, in August, 1895, there were
altogether 31,056 natives of India, 125 Eurasians, 869 Europeans of the
civil population, 6,627 native officers and sepoys, and 294 officers
with 3,206 men of the British troops stationed in India, in all 41,787
people, who had submitted to inoculation. Observations instituted among
them, especially among prisoners, soldiers and coolies in tea estates,
with regard to whom detailed records could be kept, went to confirm
the results as detailed above. In order to lengthen, if possible,
the period of immunity, the plan was formed of inoculating stronger
vaccines and in higher doses. The inoculations are now carried on in
a Government laboratory, in Purulia, Bengal, chiefly among the people
emigrating to the cholera districts of Assam, and there is no doubt
that in the course of time a marked effect upon the prevalence of
cholera in those districts will be produced and valuable theoretical
data will be obtained.
* * * * *
There was one noticeable feature about the results of the inoculation
against cholera which early attracted my attention, and this was that
while the number of attacks and the absolute number of deaths was
strikingly influenced by the operation, the proportion of deaths to
those attacked did not appear to be changed. The case incidence was
effectively checked, but the ‘case mortality’ was not reduced. The
inoculation diminished the chances of an attack of cholera--that is,
the chances of the cholera virus penetrating into the tissues of a
man; but if it so happened that the patient was attacked and the virus
found an entrance and started growing in the system notwithstanding the
inoculation, the latter would not assist in mitigating the severity of
the symptoms or reducing the fatality of the disease. In analyzing this
result further, it seemed to me permissible to assume that the vaccine
protected against the cholera microbes themselves, but did not protect
against their poisonous products, which are the cause of the actual
symptoms.
This interpretation of the facts found support in a set of laboratory
experiments by Professor Pfeiffer and Dr. Kolle, of Koch’s Institute,
in Berlin, who showed that the blood serum of animals and persons
inoculated with the cholera vaccine, as practiced in India, acquired
an intense power of destroying cholera microbes, but exhibited
no properties capable of counteracting the effect of their toxic
products--no ‘antitoxic properties’. Combined with those of previous
experimenters these results tended to prove that two kinds of immunity
could be produced separately, and it became incumbent to devise a
plan which would secure not only a lowering of susceptibility to the
disease, but also a reduction in the case mortality.
For that purpose it seemed rational to attempt the treatment with a
vaccine containing a combination of bodies of microbes, together with
their toxic products. I intended to test this plan experimentally in
the cholera districts; but, plague having broken out in Bombay, the
Government of India commissioned me to inquire into the bacteriology of
that disease, and I determined that the knowledge gained in the cholera
inoculations should be applied and tested in the preparation of a
prophylactic against the new epidemic.
The experiments I had in view involved manufacturing a material on a
large scale, and operating on it for weeks continuously. To do this
it was essential to find a way of recognizing plague growth with
certainty, so as to enable the officers engaged in the manufacture
to control the process and know exactly when they were handling the
proper stuff, and when an admixture and invasion of extraneous growth
took place. When this was solved, a drug was prepared by cultivating
the plague microbe in sterilized broth, to which a small quantity
of clarified butter or of cocoanut oil had been added. The plague
bacilli attach themselves to the drops of butter or oil floating on
the surface, and grow down into the depth of the liquid, forming a
peculiar threadlike appearance. While doing so they secrete toxic
matter, which is gradually accumulated in the liquid; at the same
time a large amount of microbial growth comes gradually down from the
surface of the liquid and collects at the bottom of the flask. When
shaken up the whole represents the desired combination of the bodies
of microbes and of their toxic products. The process is continued for
a period of five to six weeks. As the microbes of plague had been very
little studied before, and as their exact effect on the human system
was unknown, I decided not to use for the treatment living microbes,
but to use at least at first ‘carbolized’ vaccines, though the result
of the treatment might be less favorable or less lasting than that
which could be expected from living vaccines. The microbes in the above
plague growth were accordingly killed by heating them at a temperature
ranging from 65° to 70° C., and then mixed with a small proportion of
carbolic acid, to prevent the drug from subsequent contamination and
decomposition. The dose of the prophylactic was regulated by measuring
up the quantity to be injected. The requisite amount is determined by
the degree of fever which it produces. The febrile reaction varies in
different individuals, but a temperature reaching 102° and above in at
least thirty per cent of those inoculated has been found to indicate
a good material. In the cholera, rabies and smallpox vaccines, the
microbes being employed in a living state, it was essential to fix the
strength of the vaccine, for otherwise it was impossible to predict the
behavior of the microbe when injected into the system. In the case of
the plague prophylactic the activity of the microbes is arrested before
it is inoculated, and the effect can be regulated, as mentioned above,
by simply measuring up the doses in the same way as is done with any
chemical drug.
The expectation formed when devising the plan for the plague
prophylactic has been very fortunately justified, and an advance on the
results from the cholera vaccines was obtained; but I can not yet say
certainly whether this favorable result is indeed due to the particular
provisions which I had made for obtaining it.