26 president's address. 



of which were observed successfully at the principal stations. 

 The value of the solar parallax determined from all the observ- 

 ations is about 8"-80, from which the mean distance of the sun 

 from the earth is calculated to be about 92,885,000 miles. Prof. 

 Newcomb and Mr. Michelson have since made independent 

 determinations of the velocity of light per second, from which 

 they have deduced a value di:ffering very little from that 

 determined from the transits of Venus. You may easily imagine 

 how difficult a problem the astronomers have had to solve, when 

 it is considered that a second of arc is only equivalent to the 

 angle subtended by a ring one inch in diameter, when viewed 

 at a distance of more than three miles, and the correction to the 

 solar parallax is just one-third of this. Or it is what a human 

 hair would appear to be if viewed at the distance of 150 feet. 

 Such are the minute quantities with which -astronomy has to 

 deal. If then a second of arc is so minute a measurement, 

 what must we say when this second is again divided into a 

 hundred parts, every one of which represents 100,000 miles in 

 the distance of the sun. And yet this almost mathematical 

 accuracy is hoped to be obtained eventually from the combined 

 series of all the observations of the recent transits of Venus 

 over the disc of the sun. 



A total eclipse of the sun is another phenomenon which 

 always creates much interest, as on these occasions most valuable 

 observations are made on the constitution of the chromosphere 

 and corona, which are usually visible during totality, but at 

 other times hidden by the glare of sunlight. In England, total 

 eclipses of the sun seldom occur, and then only at long intervals. 

 The last occurred in 1724, and the next wiU not take place until 

 1927. Before the red solar prominences were found to be 

 observable in sunlight, by means of the spectroscope, the 

 expeditions formed for viewing an eclipse were of a more 

 interesting character than the purely scientific expeditions of the 

 present day ; as now the attention of the observers is usually 

 confined to spectroscopic and photographic observations of the 

 corona and prominences, and thus all the sentimental beauty of 

 the phenomenon is sacrificed to pure science. In 1851, 1 had the 

 good fortune of witnessing a total eclipse in Norway, and the 

 impressions then fixed on my mind of its sublime character, are 



