33© DETERMINATION OF THE PLACES OF THE PLANETS. 



tunate one. There are three sets of co-ordinates which appear to 

 be possible : 



(i) The Ecliptic; 



{2) The invariable plane of the solar system ; 



(3) The plane of the Milky Way. 

 But in each case it would be necessary to adopt a fixed departure 

 point. In the case of (3) probably either the intersection of the 

 invariable-plane with the Milky Way or the plane of the solar 

 drift (apex and antiapex) would furnish such a point. In any case 

 the departure-point could be fixed so that the resultant proper 

 motions in the adopted plane of say 1,000 bright stars should 

 vanish. If (i) were adopted, in the course of 30,000 to 100, oca 

 years the latitudes of the stars would vary by possibly 2 degrees 

 or so ; but if (2) or (3) were adopted the stars' places would only 

 change by proper motion. If alternatives (2) or (3) were adopted, 

 it would mean the computation once and for all (or at least for say 

 1,000 years) of some 250,000 star-places, and in addition the mov- 

 ing co-ordinates, i.e., Right Ascension and Declination of about 

 1,000 stars. The labour thus saved would be enormous. A very 

 large part of the time of every observatory is devoted to bringing 

 star-places up-to-date, — this labour is never-ceasing ; on the con- 

 trary it tends to augment. 



It can be safely said that had the great astronomers Lacaille, 

 Lalande, Piazzi and Bessel, to whom we are indebted for tHe 

 earliest extensive catalogues of faint stars, been in possession of 

 the photographic dry-plate, their catalogues would not have been 

 based on Right Ascensions and Declinations. 



INTERNATIONAL GEOGRAPHICAL CONGRESS 



— Preparations for the tenth International Geographical Congress, 

 to be held in Rome under the patronage of the King of Italy 

 during the week beginning October 15th, are now in active pro- 

 gress under the direction of an Organising Committee appointed 

 by the Council of the Italian Geographical Society. The Congress 

 will be divided into the following eight sections : — Mathematical 

 geography, Physical geography, Biogeography, Anthropogeo- 

 graphy, and ethnography, Economic geography, Chorography, 

 Historical geography, and History of geography. Methodology 

 and Didactics. Buildings have been specially erected for the 

 accommodation of the Congress in the grounds adjacent to 

 Castel Sant'Angelo, where the inaugural meeting will take place 

 on the date above mentioned. There will be some excursions in 

 the neighbourhood of Rome during the course of the Congress, 

 and immediately after its conclusion there is to be an excursion 

 into Central and Northern Italy, in order to visit regions where 

 geographical factors have caused particular economic and indus- 

 trial development, and another in Southern Italy and Sicily, 

 where most interestic geologic and volcanic phenomena, includ- 

 ing the ravages of the 1908 earthquake, may be observed. 



