question of the sun's distance. Indeed, the computation used until recently 

 was based upon the observations made on the last transit in 1769, before 

 the invention of accurate instruments. Photographs will be taken at the 

 different stations at various stages in the progress of the transit. Spectro- 

 scopic observations will be made in several instances. The spectroscopic 

 is more accurate than any other method for the measurement of the exact 

 moment of the second or interior contact with the sun's limb. The Ger- 

 man, Russian, English and American corps of observers, already selected, 

 are training for the occasion by practising with the chosen instruments 

 upon an apparatus used to represent the transit. Stations for observation 

 will be chosen in Russia, Siberia, China, Japan, and on sundry islands in 

 the Indian and Pacific Oceans. The importance of accurately determining 

 the distance of the earth from the sun cannot be properly estimated unless 

 one remembers that that distance is taken for the unit of measure in most 

 of the calculations of Astronomy, and that a change in the standard ac- 

 cepted will involve a change in all the distances as recorded in our astro- 

 nomical tables. 



In my inaugural address before you two years ago, I spoke of the 

 wonderful calculations of the elements of the orbit of Neptune by LeVer- 

 rier. On the morning of the 24th of March last, another confirmation by 

 actual observation was made of the existence of a planet within the orbit 

 of Mercury, to which the name of Vulcan has been assigned. Certain dis- 

 turbances in the motion of the planet Mercury had long since led LeVer- 

 rier to calculate the elements of a planet interior to it, and with a period of 

 revolution which he computed at igf^ days. Certain well-defined circular 

 black spots have been observed passing rapidly across the sun's disc, the 

 same having been seen by a French physician in 1859, *"*^ ^7 ^" °^' 

 server in Manchester in 1S62. Mr. Hind of the Twickenham Observatory, 

 England, made calculations from these and other observations, and pre- 

 dicted its transit across the sun's disc on the 24th of March, 1873, and at 

 that time it is said to have been actually seen by an observer at Shanghai, 

 China. 



It has been long suspected that Venus is accompanied by a satellite. If 

 such be the case, it is more than probable that the observations at the time 

 of the transit next December will detect the fact. 



The brilliant discoveries made by the spectroscope on its first introduc- 

 tion have been eclipsed by still greater ones made within the past two 

 years. The method of measuring the rise and fall of the hydrogen flames 

 in the sun by the variation of the lines in the spectrum has made it possi- 

 ble to keep a record of the prominent disturbances on the solar surface for 

 every day in the year not obscured by clouds. The observations of Dr. 

 Huggins, of the Royal Astronomical Society, upon the movements of the 

 "fixed" stars, have been before the public for some time. He finds by the 

 variation of the lines in the spectrum that some stars are approaching us 

 at rates exceeding fifty miles per second, while others are receding quite 

 as rapidly. Sirius is at present leaving our system at a rate exceeding 



