160 PROCEEDINGS OF SECTION A. 
The Sydney and Melbourne Observatories are among the 
eighteen institutions participating in the work. 
It is with a feeling of deep admiration that I think of the year 
1887, when the directors of these two Australian Observatories, 
with a truly scientific spirit, well knowing the difficulties to be 
faced, secured the opportunity of rendering a great service to 
science, and of raising the astronomical prestige of their institu- 
tions to the honour and credit of the colonies by inducing their 
Governments to permit and support their adherence to the 
purposes of the Astrophotographic Congress, to associate with so 
many distinguished workers in a common enterprise, which will 
certainly leave its conspicuous mark among the many extra- 
ordinary achievements of our time. You will observe that the 
work consists of two distinct parts, namely, a catalogue and a 
chart. Hach of these parts involves (for reasons to be given later) 
the photographing of the whole extent of the celestial sphere 
twice over; one series of negatives (catalogues) being obtained 
with short exposures of a few minutes, about five minutes on an 
average, while the exposure for the other series (chart) extends 
from forty to ninety minutes. 
For the purpose of allotting an approximate equal area to each 
participating Observatory, the heavens were divided into eighteen 
zones, bounded by parallels of declination, each zone being taken 
complete charge of by each Observatory. Thus, Greenwich 
and Melbourne have charge respectively of the North and South 
Polar caps; Sydney has the zone adjoining that of Melbourne, 
and the Helsingfors zone adjoins that of Greenwich. 
The intermediate zones are taken up by four other Observatories 
in the Southern Hemisphere and eleven others in the North. 
The complete list is as follows, in order of latitude :—Green- 
wich, Rome, Catania, Helsingfors, Potsdam, Oxford, Paris, Bor- 
deaux, Toulouse, Alger, San Fernando, Tacubaia, Santiago, La 
Plata Rio, Cape of Good Hope, Sydney, and Melbourne. The 
Australian contribution alone is a little more than one-tenth of 
the total. 
The labours of the past years, and the progress made, place it 
beyond reasonable doubt that the accomplishment of the under- 
taking is within reach. It may, perhaps, be interesting to some 
among you to know the principal features of the work, and the 
first conditions laid out by the International Committee, which I 
will attempt to describe very briefly, as follows :—AII the instru- 
ments employed in these operations are of the same class and 
optical dimensions, and each consists of a double telescope, 
equatorially mounted, and forming a rigid system, one for photo- 
graphing, provided with an objective of 13-0 inches aparture, and 
the other for visual observations, with an objective of 10-1 inches, 
both of the same focal length—approximately, 134 inches. 
