THE PHOTOGRAPHIC CHAKT OF THE HEAVENS. 61 



PREPARATIONS NOW BEING MADE IN SYDNEY 



OBSERVATORY FOR THE PHOTOGRAPHIC 



CHART OF THE HEAYENS. 



By H. C Russell, b.a., c.m.g., f.r.s. 



[With Plate xi.] 



[Read before the Royal Society of N.8. Wales, July 1, 1891.'] 



Last year I exhibited various photographs of stars and nebulae 

 taken with a portrait camera lens having a focal length of thirty- 

 two inches, now I am able to shew you some of the same objects 

 photographed with the new star camera of one hundred and thirty- 

 five inches focal length. One could hardly realize the extra- 

 ordinary difference between the two without seeing it. I am also 

 able to shew you the result of taking a star cluster with an enlarg- 

 ing lens which makes the equivalent focal length of the star 

 camera five hundred and sixty-four inches or forty-seven feet. 

 The success of this addition to the star camera is very gratifying, 

 because it shews how much may be added to our knowledge of 

 star clusters by this method of direct enlargement. I find it is 

 much better to enlarge the star pictures in the camera direct than 

 after they are taken, because there are always blemishes in the 

 surface used for the photograph which get enlarged with the 

 picture. The first photograph of Kappa Crucis did not cover a 

 space of one-tenth of an inch square, the star camera makes it 

 eighteen times larger and the enlarging lens three hundred and 

 twenty-four times larger. Where extreme accuracy for measure- 

 ment is required, as in these cases, the photograph may be again 

 magnified fifty times under the microscope, and the smaller 

 picture will bear no greater power, because it is the imperfections 

 in the surface that carries the image, that limit the magnifying 

 power that can be used. 



The photograph obtained with the enlarging lens on the star 

 camera speaks volumes for the stability and accurate motion of 



