50 Proceedincja of the Boi/al Society of Victoria. 



aliout equivalent focal length. This latter telescope is used 

 to keep the instrument pointed always exactly on the same 

 point in the sk}-, by watching a selected star, whicli is 

 bisected by the spider web cross in the field of the telescope, 

 and by requisite adjusting motion, kept exactly bisected 

 during the whole time of exposure. A photograph of the 

 Pleiades, obtained by the brothers Henry, exhibited 1421 

 stars, and a small nebula aroiind one of them, which had 

 never before been seen or suspected. A chart of this group,, 

 which had occupied an observer three 3-ears and four months, 

 contains G71 stars, so that one hour's photography gave the 

 position of 1421 stars, figainst 671 hi three years and four 

 months by eye observation. 



So remarkable a success encouraged the Director of the 

 Paris Observator}', Admiral Mouchez, to address a circular 

 to astronomers all over the world, suggesting that a complete 

 charting of the heavens siiould be undertaken, as an 

 international work, by the various national observatories. 

 The proposal being favourably received, an invitation was 

 issued to all ast)-onomers to attend a conference on the 

 proposal, to meet in Paris in April 1887. Fifty-eight 

 astronomers attended this congress, Austi'alia being repre- 

 sented by my colleague, Mr. Russell, of Sydney Observatory. 

 The congress agreed to the main propositions and passed a 

 series of resolutions on most of the vital points, leaving the 

 further consideration of details to several selected committees. 

 Sevei-al meetings of members of the congress have since been 

 held, the last being in March of the present year, when nearly 

 all the minor points left to the committees were settled, and 

 Admiral Mouchez declared the woi'k of the international 

 astrographic charting of the heavens had now commenced. 



The earlier resolutions fixed the dimensions and optical 

 characters of the photographic telescopes, the size and kind 

 of photographic plates, times of exposui-e, and inagnitudes of 

 . the stars to be secured on the plates. Subsequent decisions 

 allotted particular portions of the heavens to each partici- 

 pating observatory, numbers of plates to be exposed to each 

 two square degrees of the skies, and so on. Questions 

 concerning the after measurements of plates and final 

 formation of charts and catalogues remain still to be 

 disposed of. 



The summation of the work of the congress is bi ietly as 

 follows : — It was agreed to undertake a photo, cliart of the 

 heavens of all stars down to the 14th magnitude, as they 



