Observatory

CSIRO PUBLICATION ON DAGELET by Ivan Barko and Doug Morrison

This letter was written by Joseph Lepaute Dagelet (1751-1788?), astronomer with the La Perouse expedition, to William Dawes (1762-1836), astronomer with the First Fleet at Port Jackson, shortly before the French expedition’s departure from Botany Bay in March 1788.

William Dawes served on the Sirius. From February 1788, he was employed  to build an observatory at what became Dawes Point. As a member of the party sent to welcome the French in January 1788, Dawes most probably met Dagelet at Botany Bay.

In his letter, Dagelet writes to Dawes of his regret at not being able to visit the site of the observatory before he leaves, and comments extensively on Dawes’ plans for his observatory.

Link to full story.

Translation by Professor Barko (2005)

Joseph Lepaute Dagelet to William Dawes, At Botany Bay on 3 March 1788

It is with much regret that I see myself on the point of leaving you without any hope of going to visit your observatory. Mr de La Perouse claims that I am too weak to undertake such a long expedition, and the zeal he shows for my health makes it my duty to agree with him. M. Boutin [Charles Fantin de Boutin, a senior officer on La Boussole] has easily explained to me the plan you have chosen and that you are currently having carried out. I find that your q.c.[quart de cercle, i.e. quadrant] is perfectly well placed and leaves nothing to be desired from any point of view. Will you cover it with a little cone-shaped dome which turns on itself? This is something very handy for the observer, and would also protect you from the humidity of the air at night, which I would strongly recommend to you for the sake of your health. You could have it constructed in tin or iron sheeting if you have a shortage of carpenters.

I would also like your clock to be located in a such a way that you can see the face and the second hand when you stand on the platform of the q.c. As far as possible you should avoid comparisons or the need to make comparisons on machines of this order ? this will mean less discussion about your reductions and greater simplicity in your journals. Never forget to note the slightest verifications, the slightest changes and any improvements to your instruments, as such a circumstance will add confidence in those who like to argue, it will save you all those “ifs” and “buts” of disputatious people. This, Sir, is advice you doubtless do not need, and I am only offering it to you because of the absolute certainty I have that you will see it as a proof of my sincerest friendship for you and my concern for all your interests.

Permit me now to offer you a picture of the research topics which your enthusiasm and insights would make interesting and useful to science. Your integrity would bring a very special quality and true certainty. You are aware that scientists are still divided on the question: are the tides at the Equinox more powerful than the tides at the Solstice? Are they equal, or what is their force? Theory would seem to render them stronger at the solstice of Capricorn, but as far as I know nothing definitive has been observed on this question. You know that a well graduated rule [= tide pole] on a headland which does not dry out etc. the winds, and thermometers are necessary to follow in this sort of research. The strength or violence of the winds in this hemisphere would be of interest to Physics. You can easily imagine a means, Sir, to oppose to its action a perfect surface of a clearly determined size, whose force would press a spring or would move a weight which would give the relationships in all circumstances. It would be necessary to ensure carefully that this surface moves only on a horizontal plane and that it be perpendicular to the lie of the wind. These sorts of observations have never been made properly nor have they been followed up. It is possible that great benefits to naval design would result from such research. I have no doubt that you could find much simpler things than the ones I would put on paper ? your very construction will provide you with some.

If at some future stage in the development of your establishment it were possible for you to procure a sector with a radius of 6 to 8 feet, a grander enterprise, and one more worthy of your merit, would be to attempt to measure a degree of the meridian under this hemisphere. That was the greatest wish of the Academy and also my own at the outset of this campaign ? I did not despair of completing this task within 4 months, provided that the position was favourable. You know that there is a host of good books on this topic, Bouguer’s for an Astronomer seems to me the best. [Pierre Bouguer, 1698-1758, author of La Figure de la terre, déterminée par les observations de Messieurs Bouguer et de La Condamine, […] envoyés par ordre du Roy au Pérou pour observer aux environs de l’équateur […], Paris: C.-A. Jombert, 1749]

If in your purely astronomical inquiries you would devote time to the comparative research of the right ascension of the Sun and some of the stars which provide the setting of cœlum Australis, that would be of particular interest to me, and if you judged it appropriate, I would offer it on your behalf to the Academy of Sciences. If you were to observe some of Venus’s conjunctions, either superior or inferior, you know perhaps that I have studied its movements and intend to return to this research one day.

The daily variations of the magnetic needle preoccupies many minds in Europe. I have had the honour of telling you what this research amounted to. An 8 or 10 inch needle in a wooden box safely placed on one of the blocks which follow your observatory would provide a stable point to fix it firmly.

I have always wished to meet with you again to clarify these questions but I fear that I have been too lengthy already and I therefore conclude by sending you the longitude and latitude at Botany Bay:

latit. 33o 59´ 10″ long. 149o 6´ 30″ This is the position of our observatory.
+ 2.19.0_
151.25.30

Please present my compliments to all your gentlemen and to Cpt Hunter. I profit from the presence of your seamen to send you my farewells and my very sincere offers of service in France for everything you would find me capable of.

I take advantage of the offer you made to me and I would be obliged to you if you would forward or have sent to England the packet which I addressed to M. de la Lande [Director, Paris Observatory] and a letter to the Royal Military School. The latter can be entrusted to the Post but I would ask you to be so kind as to forward that of M. de la Lande to Mr de Maskeline [Nevil Maskelyne, Astronomer Royal] for him to pass it on to him, or, if you would prefer, to Doctor Sepherd, [probably Anthony Shepherd, Professor of Astronomy, Cambridge] putting a second envelope over the other, and addressing it either to the Minister in Paris or to the Minister of War.

You see, Sir, that I somewhat abuse your kindness. I have presented your compliments to Mr de la Perouse and to our gentlemen, and I am charged with expressing their general gratitude.

P.S. This morning we sent back a seaman who was almost the victim of the natives. Without the help of our chasseurs who went to his rescue it is probable that he would have been overcome by numbers. Please be so kind, Sir, in your travels to think that they, these natives, merit only a very limited measure of trust, their good faith is suspect, and I urge you not to venture too far without your weapons.

Dagelet sends his regards to Mr Donis [Dawes]. He would be flattered to go and get his errands for him in Europe, and he will do it if he can be relieved of some of his duties before his departure; he has not forgotten which topics of research hold the greatest interest for scientists at the present time. He also intends to send him the results of his observations on longitude and latitude at Botany Bay. Latitude will diverge little from 33o 59´0″ and longitude from 149o 2 or. Paris, but he will send them to him and will take the liberty of sending a dispatch for his journal before his departure ? In any eventuality he presents his compliments to Mr Donis and is jealous that he will go without having the honour of presenting his respects and without admiring the foundations of the Maskeline Observatory. We have drunk your collective health.
Translated by Professor Ivan Barko, 2005

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