xxvi. ytew Zealand Institute. 



at the point where the phase is maximum, the eclipse of the 6th May- 

 last, which was to have a duration three times as great, was looked for- 

 ward to the more eagerly, and scientific parties were sent out from 

 England, France, and America to examine the phenomenon from 

 Flint and Caroline Islands, situated to westward of the Marquesas, 

 and the nearest points of land to the central line. We have learnt, 

 by telegram, that the observations made by them were successful, 

 especially as regards the photographs taken j but it is impossible to 

 discuss the details of the results until further accounts reach us. 



TEANSIT OF VENUS. 



Next, as regards the transit of Venus. I need scarcely mention 

 that the object of observing the transit of Venus across the sun's 

 disc is to determine the distance of the sun from the earth ; — in the 

 words of Sir George Airey, " the noblest problem in astronomy." 

 Although, through the sublime discoveries of Copernicus and Kepler, 

 we have a just conception of the order of the solar system and its 

 relative dimensions as expressed in Kepler's Law: that the squares of the 

 periodic times of the planets in their orbits are to each other as the cubes 

 of their distances from the sun; yet we know not with anything like 

 absolute certainty any of these distances. But, in virtue of the law 

 just quoted, given the true distance of any of the planets from the 

 sun or from each other, and we have all the rest. The distance we 

 seek, therefore, is not alone that of the earth from the sun, but in 

 reality the base-line of the universe. 



The sun's distance was to the ancient astronomers an insoluble prob- 

 lem, owing to the want of adequate instrumental means. Aristarchus 

 gave the distance as nineteen times that of the moon, which, accord- 

 ing to our value of the moon's distance, would give that of the sun 

 under 5,000,000 miles. Even so late as the time of Kepler, not 300 

 years ago, the estimate of the sun's distance was 13,000,000 miles, or 

 less than one-seventh of what is now accepted. 



Indeed, in Kepler's time, the idea of utilizing the transit of 

 Venus, as astronomers now do, was not thought of. It was reserved 

 for the celebrated Scottish philosoper, James Gregory, in 1663, to 

 point out the probability of determining the sun's parallax by means 

 of the transit of Venus. 



As is well known, these transits occur in pairs, the first and 

 second of a pair being divided by an interval of only eight years, 

 whilst between one pair and another there are successively intervals of 

 105^ and \2\\ years. Thus, there were transits of Venus in 1631 

 and 1639; next in 1761 and 1769; the present generation has been 

 specially favoured by having seen the transits of 1874 and 1882 ; and 

 the next will not take place till 2001 and 2012. 



