Observations

Letter by H C Russell, 14 February 1891

Letter by H C Russell, 14 February 1891
Letter by H C Russell, 14 February 1891
Letter by H C Russell, 14 February 1891
Letter by H C Russell, 14 February 1891

Letter by H C Russell, 14 February 1891
Letter by H C Russell, 14 February 1891

150-154

Feby 14th [189]1

Admiral Mouchez

My Dear Sir

With this I am sending a contact print of one of my photographs of the Nubecula Major. The negative was exposed for 7h 3m and it shows that the whole of the Nubecula Major is a complicated Spiral Structure. I thought you would like to see it. and it might interest the members of the conference. It was taken with a Dalmey [sic] portrait lens 6 inches….

The photograph is one of a series I have taken of the milky way and Nubecula Major & Minor while waiting for the lens from Sir Howard Grubb.

On the plate on the north side of the centre are 4 dark marks in a line. And on the preceding side a large dark mark. All these are faults in the plate left by the maker.

I have been using a developer which Mr E J Hunt A.M.L.C.E. has designed. It is in fact a modification of an old developer but it seems to me to be very much better for star photographs than any other that I am acquainted with. It gives brilliant contrasts and has the advantage that the development can be limited by time and not by what one sees. It might for instance be a resolution of the committee that all should use this and keep the plate 4 minutes in solution A and 2 minutes in solution B: I should be glad if the Committee would try some experiments.

I have done so and find that I get much better results: denser star points and more certain development; with this developer than with any other. The negatives I have sent were developed with it and not intensified.

Referring now to the Zones allotted to the different observatories. I should like to say, that I shall be glad to take any Zone which the Conference may allot to Sydney. I am anxious to do everything in my power to help in carrying out the work of the Conference. My reason for speaking of this is: that I shall not be at the Conference. And that I see you have received one letter objecting to the new allotment of Zones Proposed by the Committee.

Feby 14 [189]1

Formula for Development

Solution A
94 grammes sulpis sodae
2 grammes S….ylic acid
Alcohol 0.004 litre
Glycerine 0.008 litre
0.591 litre water

Solution B
6 ½ grammes Bromide Ammonium
0.015 litre Ammonia .880 strong
0.591 litre water

To develop take of Solution A 0.059 litre and add to it at the time; 3 grammes pyrogallic acid. Pour this over the plate and keep it on the plate 4 minutes. Pour off the solution and pour on to the plate 0.059 of Solution B. Keep this on for 1 or 2 minutes and the development is complete. Then wash the plate and fix it as usual.

The plate must not be washed between the use of solutions A and B it is necessary to mix A and the pyrogallic at the time of using, it will not keep many hours it may be used for several plates.

With reference to the proposed methods for securing defined star magnitudes 11 and 14 on the photographic plates. I would submit the following considerations.

If the time necessary for exposure of the plate in order to secure the desired magnitudes is to be determined by experimental plates on well known test objects. It will often happen that in the course of the evening & night the translucency of the Atmosphere will change, and the plates for the chart of the sky will be too much or too little exposed. And this may very well take place without the knowledge of the Astronomer, hence it will be necessary either to have two telescopes simultaneously at work one pointed to the test object and the other to the plate, and test it by means of the stars of known magnitude on it. Of course it will not be possible to do this at the time. The plates would have to be developed and they would be wet and unfit for examination. Moreover the time lost would be a very serious delay, if indeed the work could be done in this way at all. It follows then that each negative plate must be examined when measured to see if the exposure has been right. If it has not been right. Then a correction derived from measures of the known stars on the plate must be applied to the magnitudes of the new stars which are found on the plate.

I think therefore that the best method of securing the desired magnitudes of the plates for the chart. Will be to expose the plates long enough to be sure they are there. It would result from this: that in the great majority of cases the plates would be over exposed and the correction to be applied to the star magnitudes would always have the sign -. and there would be a great saving of time in the work of taking the photographs of the sky. and the additional time given to measuring them would not be much. Because as I have before, pointed out the magnitude of each star on the plate must be examined. And if necessary corrected for any error of exposure, by the error found on known stars on each plate, and therefore since there will be few plates with exactly the right exposure and which require no correction it will I think be much better to have all the plates subject to a correction for magnitude derived from the known stars on it: and in this way save a great deal of time in taking the photographs for the chart.

Yours faithfully
H.C. Russell

Related