The Comet Daniel.

Progress, 1 October 1907, Page 434

The Comet Daniel.

We have received, tfte following letter from the Government Astronomer, Sydney :—": — " In your excellent publication for September, I notice an article on the comet Daniel which is well put together, and reflects credit on the writer in having assembled facts from previous authorities on the subject for your readers The photographs are very good, but is Fig.l a photograph of the comet, or is it a photograph of a drawing ? With twenty minutes' exposure, (4.45 to 5.5 a.m.) both the crescent moon and the stars would have moved a good deal, and their images would, therefore, be blurred ; but in your reproduction the images are very sharp, also the long streamers of the tail of comet do not show any tapeiing , they are as well denned towards the extremity as close up to the nucleus. A study of the other photographs will give you an idea of what I mean. The photographs I had taken at our branch observatory of this comet were a great success, but owing to our astrographic telescope being set to only cover 2 sq. degrees (and I did not wish to alter the focus) a small portion of the end of the streamers was lost." In connection with the above letter we have received the following reply from Dr. Kennedy :—": — " I beg to say that Fig. lis a photograph of a drawing of a photograph of the comet. In the original negative the halation caused by the moon was so great that it spoiled the picture considerably, blotting out a number of the stars and even a part of the comet's tail, near the centre. I therefore had as exact a drawing as possible made, by pricking through a print from the negative the positions of the stars, comet and moon on to white cardboard, on which the stars, comet and moon were then drawn in the positions marked by the pin pricks, and this drawing was then photographed. The star images in the original negative show a slight trail when examined with a magnifying glass, but the image of the moon does not show any blurring, no doubt because the difference in the motions of the moon -and of the comet was not sufficient in that short time to show with a short-focus lens."