Cloué is known
for his hydrographic work around the coasts of Newfoundland culminating in
his Pilote de Terre-Neuve (Paris: Lainé, 1869 and Paris: Imprimerie
nationale, 1882). In 1857 Cloué had Miot under his orders on board
the Ardent, Miot's first posting to Newfoundland. It was during this
voyage that began a collaboration that was destined to last several years
(see Tréfeu's biography). In the following letter to the Commodore
of the Newfoundland station, Mazères, he describes Miot's work (text
translated from the French).
|Archives nationales, Paris, MAR BB4 797 (1857) - Extract (translated).
Port of St. John's, Newfoundland, 27 September 1857
[...] One of the officers of the Ardent, Lieutenant Miot, took up photography during his last period of leave. He is remarkably successful, Commodore, as you have been able to see for yourself. 1 I have given some thought to utilizing this new science, which, until now, might have appeared to have no more than an artistic side, for our precision work, and I believe that, thanks to the ability and the intelligence of Mr. Miot, I have achieved results that give extremely high hopes for the future.
Theodolite readings taken from the main points of triangulation require a certain experience of drawing to produce the views, which, with the aid of the angles that are included in them, are invaluable in later recreating the contours of the coast and the main features of the terrain.
Henceforward, a few angles taken with the theodolite will suffice, and the readings will be completed by a photographic view on which the angles need not be calculated until the moment when the plan is drawn. I have had Mr. Miot take several of these views, taking care that the focal point of the instrument's lens is in the same position for each of the views, so that the horizontal distances on the print always represent the same number of degrees in the angle.
When taking measurements from the photographic views, with a graduated metal ruler, of the distances that separate the verticals drawn from various readings, I have frequently obtained an accuracy to within one minute compared to the angles provided by the theodolite readings.
A metal ruler with a vernier scale would easily give tenths of millimetres, in other words forty seconds (since generally 3 millimetres give an angle of 20 minutes). Is this not a very satisfactory approximation?
Mr. Miot's camera has a lens of 0m085 and has only plates measuring 0m27 by 0m22 with which one can record only a field of view of approximately 25 degrees. Hence one needs at least 13 plates to make up a complete panoramic view, covering the full horizon. With a lens that has a greater diameter, one could reduce this number to eight or nine. In fact, theodolite readings rarely cover the full horizon. Hence, with five views from a powerful instrument, one could obtain most of the necessary readings. Three carefully-selected camera locations within a broad area would be sufficient to obtain a reproduction of the land and the indentations of the coast with the greatest accuracy. In addition, this information is an excellent check on that taken with the theodolite; for if, with the latter, one makes a mistake (which happens to everyone), the photograph will reveal it immediately, for it never lies. If the photograph is sufficiently sharp, measuring the distance between the verticals gives the horizontal angle.
In order to be certain of having the vertical for every point, it would be necessary to place a small plumb line inside the camera body so that it would be reproduced on the photographic image.
When the focal point of the instrument is at a particular location, each millimetre of the image has an angular value which changes as one modifies the distance between the plate and the focal point of the lens. In the dark room it is possible to set up a graduated lateral ruler so that one can determine the angular value of a millimetre on the image according to where the instrument is placed. It would probably be sufficient (and I speak with some experience) to maintain a constant position of the lens in relation to the plate for all of the photographs.
The hygrometry of paper can result in the dimensions on a print that has been fixed being noticeably different from the image on the glass plate. In that case one can take measurements directly from the plate. In any case, a reading taken with the theodolite can serve as a scale for the photographic view printed on paper.
In spite of the difficulties encountered on board in setting up a small, suitably-equipped photographic laboratory, Mr. Miot has succeeded in producing photographs of harbour entrances which offer the highest promise of what this highly-skilled officer could produce with an instrument that has a powerful lens and if he were not frequently halted by an inadequate supply of chemicals.
The camera on board is the property of Mr. Miot. This young, intelligent officer placed it and all of his chemical supplies entirely at my disposal for all of the experiments that I wished to attempt. I made frequent use of them, always with Mr. Miot; for, since I am not a photographer myself, I could not have achieved anything without him.
The supervision of the completion of the four sheets on Fichot that are at the engraver's and the detailed correction of the proofs would alone require my presence at the Dépôt de la marine; however, I also have to write up the work carried out this year and listed above, the publication of which is urgent.
Mr. Miot took a very active part in this work. His collaboration would be useful for me to pursue this writing. In addition, it would be desirable for this officer to come to Paris to keep up to date with the advances that have doubtless been made in photography over the past year.
(signature: le Capitaine de frégate commandant l'Ardent Cloué)
P.S. As soon as I arrive in Lorient I shall send the transcripts of our observations accompanied by photographic views via the Maritime Prefect.
(copy certified as authentic by Mazères, Commodore of the Newfoundland naval division)
1. This comment appears to indicate that the ministry had already received copies of prints by Miot, and the post-script shows that others were soon to follow. What happened to them? (Note by the authors of this web page.)