162 PROCEEDINGS OF SECTION A. 
complete series consisting of 22,054 separate and independent 
photographs. 
It would be hardly appropriate to enter here into further 
technicalities and details. Suflice it to say that, so far as securing 
the negatives with the required precision and efficiency, all the 
difficulties have been gradually conquered, and the work has pro- 
ceeded satisfactorily for some years past. 
One series, namely, that with short exposures, for the star 
catalogue, has been accomplished by the majority of the co-operating 
Observatories. Both Sydney and Melbourne terminated their 
share some time since. 
In regard to the second series, with long exposures for the 
chart proper, a few Observatories are fast approaching completion, 
some are making fair progress, and others (the South America 
Observatory, for instance) have not yet commenced. 
Sydney is well advanced ; but in Melbourne we have not been 
able to go ahead with the desired speed lately, but the conditions 
have greatly improved more recently, and the work is now pro- 
ceeding quite satisfactorily. 
As we are bound to complete our Australian share of astropho- 
tographic work, let us see what still remains to be done in this 
respect. 
Actual photographic operation for the chart proper will occupy 
at least four years. In the meantime, the negatives of the 
catalogue or short exposure series require to be measured and 
reduced. 
The nature of the measurements consists in determining the 
rectilinear coordinates of each star on each plate, taking the 
centre of the plates as the origin. 
The resolutions of the Conference held in Paris, in 1896, 
demands that these co-ordinates shall be correctly determined 
within 0:2”. That is the linear distances of a star from the 
central lines of the reticule, as measured micrometrically, ovght to 
be correct within 0-003 millimeters, which is equivalent to a little 
more than ;>25,sth of an inch. 
This is the maximum error allowable. Of these distances there 
will be probably half a million to measure for the Australian 
portion. 
The measures are then to be subjected to various corrections, 
and prepared for publication as early as possible. The labour 
involved in these operations exceeds by far that required for the 
whole actual photographing, and will take perhaps seven or eight 
years to accomplish, provided a special bureau is created for the 
purpose with half a dozen or more assistants. 
This is not all. In order that the precise positions which the 
stars actually occupy in the heavens may be deduced from the 
position of their photographic images on the plates, it is necessary 
