these local committees and before the people At the same time the association desires to put prominently forward a thoroughly conservative and scientific estimate, indorsed by the highest medical authorities, of what the State may expect to accomplish in the reduction of the tuberculosis death rate by 1920, if, by 1915, Every county in the State has a hospital or sanatorium, Every city and village an adequate number of visiting nurses, Every community of over 5000 people a free dispensary, All living cases of tuberculosis are reported to the health officer, Every living case is in a hospital or sanatorium or under proper supervision at home, Thorough disinfection is given to premises which have been occupied by a tuberculosis patient after every case of death or removal. TUBERCULOSIS CAN BE PREVENTED Of this we are assured on the highest scientific medical authority. Dr. William H. Welch says: It is in my judgment a conservative statement that at least one-half of the existing sickness and mortality from tuberculosis could be prevented within the next two decades by the application of rational and entirely practicable measures, and I believe that we can look forward to a much larger success. Dr. Frank Billings, of Chicago, recently wrote: The State of New York is to be congratulated upon the fact that the propaganda of the fight against that terrible, but nevertheless prevent able and eradicable disease, tuberculosis, has been so efficiently applied as to noticeably diminish the morbidity and death rate of the disease at the present time. should be practically driven í. Dr. S. Adolphus Kn If such a thing as havin combined efforts the grea New York City, Why should not t To cut in half the It is still further to be congratulated upon the fact that the measures which are so efficacious in the fight against the disease will be extended throughout the entire State by the year 1915. At that time with at least one dispensary in every county in the State and an additional dispensary in every city and village of over 5000 inhabitants, with a tuberculosis hospital with ample provision for the humane care of moderately advanced cases in every county, with tunity for so efficient registration of substantially all living portance with cases in the State, with adequate disinfection Let your city on the Roll of 1 Human lives of all infected foci, and with proper provisions Duty is meas. for the social relief of wage-earners, the disease tunity. Ever the State with 1910.3. Interval in years. 77.5 79.1 HALLEY'S COMET AS IT APPEARED IN 1835 (From a sketch by Struve, probably somewhat exaggerated) 76.5 former year William of Normandy came over to England, and the Bayeux tapestry 78.9 gives a representation of the popular belief 77.6 of the connection of the comet with the con76.2 quest of England and the death of Harold. 77.0 75.2 74.9 76.5 CALCULATING THE RETURN OF A COMET 76.7 74.5 without a break to Even 225 years precomet observed that Halley's, but the recJutely conclusive. The of perihelion passage, or Comet was nearest the sun, acing the day and month times are expressed in deci1910.3 meaning that the erihelion three-tenths of a rst of January. The past the comet most worthy of of 1066 and 1456. In the At the last appearance of the comet in 1835-36 its position in the sky was measured by many astronomers. From its mo tions as exhibited in these measures it was possible to calculate the comet's journey off to hundreds of million of miles from the sun. As the comet traveled through space it went close to some of the bodies of the solar system. These planets pull the comet exactly in the same way as does the sun, but with less force, since they weigh much less than the sun. The planets might accelerate or retard the motion of the comet, depending on their relative positions. These "perturbations" of the comet's motion it is necessary for the there was no attendant war, and likewise there have been great wars without their attendant comet. We do not recall any serious outbreak of hostilities following in the train of Coggia's fine comet of the year 1874, and certainly no one can point to a remarkable comet at the time of the recent Russian-Japanese war; and that surely was a great war. It would, indeed, be remarkable if wars and comets did not at times appear together, but to imagine that a heavenly body of such small weight as a comet could be able to disturb the affairs of men is perfectly absurd. This has even less foundation than the superstition that the moon has an influence on weather, for all the statistics of modern science show that the weather is absolutely independent of the moon. HOW NEW COMETS ARE DISCOVERED New comets are usually discovered by an astronomer after careful and diligent search with a telescope of low power. Such a quest demands an almost infinite amount of patience in nightly scanning the heavens up and down in the hope of detecting a stranger in our midst. So close a watch is kept that seldom does an intruder escape the eager eyes of the sentries and attack the citadel as happened with the first comet of the year 1910. Comet A, 1910, eluded all eyes till it became very bright and quite close to the sun, and an astronomer was not the first to see it. Sometimes a comet is accidentally found on a photographic plate exposed for some other purpose, such a one being the Morehouse comet of 1908. If the comet is not a new one, but the return of one already known, it is possible to direct the telescope to the point in the sky where it is expected, and a long exposure photograph may detect it. Halley's comet was discovered on September 11, 1909, on a photograph taken for the purpose by Prof. Max Wolf, of Germany. At the time the comet was very faint, and looked exactly like a very small star. Up to the time of Sir Isaac Newton nothing was known of the behavior of comets. Some thought they took their origin from the sun; still others that they might have been volcanic matter thrown off from the moon, while others imagined they might be phenomena of the earth's upper atmosphere. Comets are much too large to be the result of volcanic action; still modern science has no adequate explanation of where they come from, though it seems certain that their home is in the solar system. After Newton had firmly established the law of gravitation and had shown that all the planets and satellites of the solar system obeyed it, he inquired whether comets did not do likewise. While wondering over these matters the great comet of 1680 appeared and gave him the chance, and he showed that not only did comets obey gravitation and travel about the sun in obedience to it, but he explained how, from observations on three nights, it was possible to calculate the comet's path. If the comet moves in a closed curve it is called "periodic "; it returns to visit the sun at short or long intervals, depending on the size of the curve, and it then moves in an ellipse. Every child knows that an ellipse is drawn by sticking two pins firmly in a piece of paper, then taking a piece of string, joining the two ends together and tracing around with a pencil. In such a curve does a planet like the earth, or a periodic comet, move, and with the sun at one of the foci. The earth's path approximates much nearer a circle than the orbit of such a comet, but none the less they both move in ellipses. " As very often happens in the case of a very great man, Newton was of a shy and retiring disposition, and it is possible that his great work, the "Principia," would never have been published had it not been for his friend Edmund Halley, professor at Oxford, who even went down into his own pocket for part of the expense of publication. Halley, born in 1656, was thirteen years Newton's junior. Following the method of Newton, and, as he tells us, after a prodigious amount of labor," Halley, in 1705, published the orbits of no less than twenty-four comets. Of these there were three that seemed to have the same paths about the sun,-i. e., their distances from the sun when at their closest points and the inclination to the ecliptic were the same. These were a comet observed by Peter Appian in 1531, one observed by Kepler in 1607, and one which appeared in 1682. Moreover, the celebrated comet of 1456 seemed to fit in with these three and seemed to point to the same comet returning after an interval of seventy-five or seventysix years. When would be the next return? Halley was keen-sighted enough to see that Jupiter or Saturn might accelerate or retard. the motion of the comet if it came near one of these big planets, and by a guess, having in it the element of inspiration, he predicted that the end of 1758 or the beginning of 1759 would see the return of the comet; and, being proud of his nationality, he called upon "candid posterity to verify the claim which was first made by an Englishman." Halley died in 1742. As the time for the comet approached the greatest enthusiasm was aroused in the prediction. In the meantime mathematics had been greatly improved and the art of calculating vastly facilitated. Clairaut, the Frenchman who took up the problem, found that the comet would be retarded 100 days by the action of Saturn and 518 days by Jupiter, or 618 days altogether, and he gave the date of passing closest to the sun as April 13, 1759. The comet was discovered on Christmas Day, 1758, and passed the sun just one month before the predicted time, a magnificent triumph for exact astronomy. The comet was a splendid object in the skies and likewise again at its appearance in 1835. This comet is now close to the earth and sun and is of the greatest interest to the astronomical world. THE PERIODICITY OF HALLEY'S COMET As this was the first periodic comet to be observed, the scientific interest in it has been very great, and previous visits to the earth have been carefully investigated. As is given in Table I, authentic returns of TABLE 1.-PAST APPEARANCES OF HALLEY'S COMET HALLEY'S COMET AS IT APPEARED IN 1835 (From a sketch by Struve, probably somewhat exaggerated) 76.5 former year William of Normandy came 77.6 over to England, and the Bayeux tapestry gives a representation of the popular belief 77.6 of the connection of the comet with the con76.2 quest of England and the death of Harold. 77.0 1111 218.2. 295.2. 373.8. 451.5. 530.8. 607.3. 684.8. 760.4. 837.2. 912.2. 75.1 77.1 77.0 78.6 77.7 79.3 76.5 77.5 75.6 76.8 75.0 1066.2 75.2 74.9 76.5 CALCULATING THE RETURN OF A COMET 76.7 .74.5 At the last appearance of the comet in the comet date back without a break to 1835-36 its position in the sky was measthe year 11 B. C. Even 225 years pre- ured by many astronomers. From its movious there was a comet observed that tions as exhibited in these measures it was was undoubtedly Halley's, but the rec- possible to calculate the comet's journey off ords are not absolutely conclusive. The to hundreds of million of miles from the sun. dates give the times of perihelion passage, or As the comet traveled through space it went the time when the comet was nearest the sun, close to some of the bodies of the solar sysand instead of placing the day and month tem. These planets pull the comet exactly in of the year the times are expressed in deci- the same way as does the sun, but with less mals of a year, 1910.3 meaning that the force, since they weigh much less than the comet came to perihelion three-tenths of a sun. The planets might accelerate or retard year after the first of January. The past the motion of the comet, depending on their appearances of the comet most worthy of relative positions. These "perturbations" of note are those of 1066 and 1456. In the the comet's motion it is necessary for the from the earth. In these HOW TO FIND HALLEY'S The diagram on opposite page shows the relations of the paths of the earth, comet, Venus, and Mars about the sun. The planets all move about the sun in the same direction, which is opposite to that taken by the hands of a clock; the comet, unlike the planets and all other comets of short period, moves about the sun in the diametrically. opposite direction. The diagram shows that the comet is nearest the sun on April 20. To find the distance with respect to the earth, join simultaneous positions. For instance, on March 26 the line from earth to comet passes through the sun, and if we would place ourselves at the earth in the diagram, and look at the sun, we would see that the comet astronomer to calculate, and if the comet on the date moved from the left of the happened to pass close to a great planet the sun to the right of it. We all know perturbations might be very great. By re- that a body to the left of the sun as we face ferring to the table, it will be seen that the it sets after the sun, and if to the right of time occupied by the comet in returning the sun the body is visible in the morning changes considerably, the difference between sky before sunrise. Hence on March 26 the least and greatest is as much as five years. Halley's comet passed the sun and became a At the 1835 appearance the calculations morning object. But it gets away from the were very simple, but for the 1910 appear- line of the sun very slowly, and it will be the ance were exceedingly difficult due to the middle of April before it is at a far enough close approach to Jupiter. In spite of these angle from the sun to be well seen. Followdifficulties two Englishmen, Cowell and ing successive positions it will be evident Crommelin, calculated the time of perihelion that on May 1 comet and Venus are very passage within three days of the actual time, close together, and consequently they should and this, too, when the comet took nearly present a magnificent spectacle in the mornseventy-five years to make its return! By ing sky, especially so as Venus is then almost pointing the telescopic camera to the posi- at her greatest brilliancy. Following still tion in the sky calculated by them, Wolf dis- along with simultaneous dates we see that on covered the comet seven months before it May 18 the comet comes directly between should be closest to the sun, when still at a the earth and the sun. Its motion carries distance of three hundred millions of miles it by the sun into the evening sky, where it HALLEY'S COMET, THE SUN AND THE EARTH |