286 PROCEEDINGS. 



Conference certain results were shown, which promise a solution* 

 of the difficulty, but in these, although there is little doubt that the 

 photo is made as permanent as the glass itself, because the photo 

 is actually melted on to the glass and made part of it, the heat 

 necessary to do this is sufficient to melt the glass, and generally 

 put it out of form, so that no satisfactory measures can be taken 

 on such a plate. M. Henri acknowledged that this objection was 

 fatal co the process in its present stage, but he said he was still 

 experimenting and hoped to be able to burn in the photo without 

 melting the glass. As a great favour one of these vitrified star 

 photos was given to me to bring to Australia, and it is this that 

 I have to shew you to night. The photo represents a part of the 

 constellation Cassiopeia, in one of the richest parts of the milky 

 way in the North. Assuming this plate to be on the same scale 

 as all the other Paris photos, viz., 1 millemetre to 1 minute of arc, 

 we have a part of the heavens measuring 132 minutes by 162 

 minutes, or about five square degrees, and on that the photograph 

 shews 5,000 stars of all sizes. If the same cluster had been 

 mapped out by the old method of measuring with the telescope 

 and then plotting on to paper, it would have taken one observer 

 working six hours every night 422 days to attain the same result. 

 It is estimated that the star photos, including all to the 11th 

 magnitude, will record the positions of one and a-half millions of 

 stars in the same way as they are upon this plate, and that 

 ultimately all these stars will be measured and catalogued in 

 books. Taking as a moderate estimate half-an-hour for each star,, 

 that is to measure and catalogue it, one man would have to work 

 at the rate of six hours a day for 417 years to get through the 

 work. Of course, the work is not going to be done at this rate ; 

 but these facts obviously call for that united effort which it was 

 the object of the Paris Astronomical Conference to secure. 



"I have here another photograph shewing the nebulae in Orion, 

 which I am sure you will all be pleased to see, for it is no longer 

 dependent upon the unknown peculiarities of the observer, whose 

 eyes have, it may be, unknown peculiarities in their sensibility to> 

 light or to colour or faint differences of these ; but we have here 

 the actual record of the light itself upon known chemicals under 

 known conditions, which can be repeated and varied at pleasure. 

 This photo was taken by Mr. Common with his own 3ft. diameter 

 reflector, and is a just reward for his unlimited perseverance and 

 ability ; perhaps one of the most hopeful things about it is that 

 success so far has nerved Mr. Common's arm, and made him feel 

 that better results still are possible with him, so that now every 

 moment that can be spared from other engrossing occupations, 

 is given to the grinding and polishing of a silver-on-glass mirror, 

 five feet in diameter, which when completed — and it is fast 



