Letter by H C Russell, 6 February 1891
pages 142 – 145
Febry 6th
Admiral Mouchez
The Director of Paris Observatory
My dear Sir
I am sending you with this such proofs as I can that my personal absence from the conference of Astronomers which is to meet in Paris on 31st of March next is not due to any want of interest in the work, but simply to my inability to leave my duty in Sydney, for so long a time as would enable me to be present at the conference.
You are I think aware that I ordered the photographic objective from Sir Howard Grub[b] in September 1887 and I did not receive it until 19th September 1890 or just 3 years. In one of the papers herewith I have given details of what has been done since then. Suffice it to say here that I have the instrument in complete working order, and that I have sent herewith some photographs taken with it which seem to prove…. the focus is very satisfactory, and that the instrument is a good one in every respect.
…. one pointed out in one of the papers herewith that…[w]eather has been so cloudy, and unfavourable for [de]licate work: that it has been very difficult to get [ho]urs of fine weather sufficient to thoroughly test…. focus. but I think I have succeeded in finding [i]t and in showing that it is highly satisfactory. The photo.… Argus, was specially taken to show a plate covered [wi]th stars, as a test of definition all over it.
The photo of the Pleiades was taken under disadvantages…. is very far from our Zenith; and the weather has [be]en very hazy. The great difficulty I have had to contend with has been the inferior sensitive plates. They are very unequal in quality; and almost every plate has serious blemishes in the glass or the chatine. but they are the best I could get.
I have ordered sensitive plates from England and America: but they have not arrived yet.
In a previous letter I mentioned that we …… ….ted all the guiding stars excepting a few….. we are about to observe with the Transit [Ins]trument. Not aware what the Committee have recommended about the marking of plates, but I should ….. to suggest to the Committee that it is de[s]irable to cut one corner off each plate, and …….. at be a mark common to all makers of p[l]ates. Then on the corner let each maker of plates …… his own number followed by the initial letters of [h]is name. Every sensitive plate could then be traced [fro]m the time it was made till it was a finished [pho]tograph. Each maker could easily keep his …… numbers consecutive. and there could be ……[co]nfusion. [sic] at the same time plates could be nicely …..ked before they were coated with gelatine. It [wou]ld be a great convenience and saving of time …. The Observatory, if all the plates were so numbered.
Most inconvenient to put numbers on the plates … the Dark room before using…. I have no reseau or good plates I have…. attempted to put lines upon the plates sent [w]ith a view to measurement, and the glass is so uneven …. It is difficult to make contact prints. [I] am looking forward to the arrival of the reseau and some of the sensitive plates plates which I have [o]rdered, and will then at once begin photographing my Zone, and am looking forward with pleasure …. The receipt of a copy of the report of the Committee giving particulars of the methods [a]nd processes to be employed in the work.
Under separate covers I am sending description of the essential parts of the Telescope and plate holder, and in print a description of my clock control which works exceedingly well. Also photographs of the Telescope and clock for moving it.
I do not know what are the limits of focal length allowed in the work, but the one I have received from Sir Howard Grubb is 11mm too long. Measuring the focal length from the back of the objective to the surface of the sensitive plate it is 3448.4mm calculating it from the measured distance of ……. stars and photograph it comes to 3450.1 and it ought to be (in order that 1mm=1’) 3437.3
I shall be very glad to hear if this error is too large otherwise the objective seems to give small and remarkably well defined images of the stars.
My letter is already too long, and I must close it regretting very much my inability to be present at the Conference.
With great regard
Believe Me
My dear Sir
Yours very faithfully
H C Russell
H. C. Russell continues his correspondence with notables of 19th Century science. Here he addresses Rear Admiral Ernest Amadee Barthelemy Mouchez, Director of the Paris Observatory 1878 – 1892 and the initiator of the Carte du Ciel, a project to photograph the entire sky in detail.
Russell had been to the congress at the Paris Observatory in 1887.