Auckland Institute. 87 



Fourth Meeting : 16/A Auyust, 1909. 

 Professor C. W. Egerton, President, in the chair. 

 Professor H. W. Segar, M.A., deUvered a lecture on " Comets." 



The lecturer dealt in the first instance with the general features of comets. The 

 special features of the more famous comets were then described. Halley's Comet, in 

 particular, was treated at some length, in consideration of its approaching reappearance. 

 The great fame of this comet results firstly from the fact that it was tlie first comet to be 

 discovered as ])eriodic. Halley, in making this discovery in 1705, made one of the earliest 

 practical applications of the knowledge first given to the world in 1686 in Newton's 

 ■' Principia." A .second feature that makes Halley's Comet famous is that, of all the 

 comets that have reasonably small periods — say, less than a hundred years — it is the only 

 one that ranks amongst the great comets which are conspicuous to the naked eye. The 

 varied attractions of the planets make the period of Halley's Comet vary from about 

 seventy-four to seventy-nine years. Calculations made for its next appearance by 

 prominent astronomers differ by several weeks in their results as to the time of perihelion ; 

 but it seems reasonable to believe that the comet will be nearest the sun not earlier than 

 about the 12th April or later than about the 10th May next. The prospects of the 

 approaching visit are bright for the Southern Hemisphere, in spite of the fact that appears 

 to be a necessary deduction from the nature of a comet's tail — namely, that the mass 

 of a comet is less after each visit to the neighbourhood of the sun. The circumstances 

 of the comuig visit are very similar to those found to exist in 1066, when the comet was 

 a great object even in the Northern Hemisphere. When nearest the sun, and for some 

 time after, when the comet will be at its best, it will be a morning star, and mu.st be seen 

 before sunrise. Owing to the comet lying near the ecliptic, and to the fact that m these 

 latitudes at that time of year and before sunrise the ecliptic cuts the horizon at a large 

 angle, and lies high in the heavens, the comet, rising as much as an hour and a half before 

 the sun, will be well up in the sky before the sun rises, and will be seen for some time 

 without much interference from twilight, with the tail stretching upwards from the 

 horizon. In the northern latitudes, however, the reverse will be the case : the ecliptic 

 will lie low in the heavens, and the sun will rise very soon after the comet. 



There will be a total eclipse of the sun on the 8th May, 1910. It may be possible 

 to see Halley's Comet during this eclipse. Such a view of the comet would be exception- 

 ally good, for the sun's light would be cut ofl^ before meeting the atmosphere, and the 

 trouble from twilight, which is an atmospheric effect, would be eliminated. The Ime of 

 totality of the eclipse, however, only touches land at its north-eastern extremity ui 

 Tasmania. Further, it seems possible that the comet may have set below the horizon 

 before totality is reached. We shall want to know more certainly where the comet is 

 in its course before we can decide. The earliest jihotographic observations of the comet, 

 which are sure to be made within the next few weeks, will give us the necessary informa- 

 tion. If the event should turn out favourably, there should be many a pilgrimage made 

 to Tasmania on the occasion. 



In concluding his lectiu'e. Professor Segar said that this was the tercentenary of the 

 first making of a telescope by Galileo, and its first application to astronomy. It was 

 worth consideruig whether the time had not arri\-ed when a national observatory should 

 be established in this country. New Zealand stood easily third in ])opulation and wealth 

 among the Australasian States. New South Wales had established a fine ob.servatory, 

 and Victoria had set up a great' telescope before they had attained the position in which 

 New Zealand stood to-day. We inherited the scientific knowledge discovered by the 

 genius of our ancestors ; it should be both oin- privilege and duty to do all possible to 

 further extend its boundaries. 



