Started: nov 15, 2004
Last Update: june 17, 2005

The telescopes

Introduction

Apart from the telescope on the quadrant, there are two more telescopes visible in the painting.

The first is in the foreground on the floor, under the celestial sphere with a green exterior covered with fleurs de lys. It looks like a multi-tubed Campani telescope of 7 feet in length with the smaller tubes at the side of the ocular partly extracted.

The second, longer telescope can be seen in the background just above the head of Colbert and next to the observatory. The pole and the rope and pulley is very reminiscent of illustrations of the observatory like the ones shown here. I estimate it's length at 15-20 feet.

Al van Helden indicated (personal communication dec/22/2004) that the telescope in the front looked like the 10-meter instrument Campani made for the Medici in the mid-sixties.Campani sent a 34-foot telescope to Cassini in 1671 or 1672, the objective of which still survives (in the old observatory). The one in Florence is 202 cm long and 14.5 cm in diameter. He suggested that this could be the 34-foot Campani telescope.

A lighter version of the image above, providing a better view of the part on the right

Van Helden provided a link to the IMMS website where I found the following description of the Florentine telescope mentioned above.

IMMS: V.51 Terrestrial telescope
Maker: Giuseppe Campani
Date: 1665
Place: Italian
Materials: Wood, cardboard, leather
Dimensions: Length c. 12000 mm
Current inventory: 3185
Large terrestrial telescope consisting of ten wooden tubes covered with cardboard. The largest is additionally covered with green leather with gilt tooling and the Medici coat of arms. It houses the wooden mount for the objective lens. The other tubes are covered with red marbled paper. The smallest contains the compound eyepiece. The objective lens V.6 and the compound eyepiece V.7 belong to this telescope. The compound eyepiece inserted in the telescope carries the inscription "lente meno acuta" ["less acute (i.e., less powerful) lens"]. The tube in which it slides has two inscriptions: "Per la lente più acuta" ["for the more acute lens"] and "Lente meno acuta" ["(for) the less acute lens"]. The magnification is 223 or 112, depending on the eyepiece. Toward the mid-1660s, Giuseppe Campani built a telescope of 52 palms (11.6 m) that—in a paragone degli occhiali [one of several telescope competitions]—proved superior to one made by Eustachio Divini. In 1665, Campani presented another instrument of the same length to Grand Duke Ferdinand II de' Medici, which is the instrument here described. On July 11, 1665, the Grand Duke observed Jupiter and its moons.

Notice the various similar features: green leather exterior, covered with gilt, the presence of emblematic ornaments.

Checking the date

As Al van Helden suggested, I started to collect references to the 34-foot telescope in order to get a more specific date of it's arrival in France. The first difficulty I encountered was the discrepancy in values of the length (34-36 foot), depending on (probably) either the type of foot (modern units of 30.48cm, French units of 32.48cm or Dutch 'Rijnlandse voeten' of 31.4cm) that was used and what was actually indicated (focal length or the length of the tube).
My first source was the OC which resulted in the following references.

OC VII: 1915: 16 dec 1672 “Monsieur Cassini qui loge dans l'observatoire m'a dit qu'il a essayè celle de Campani de 36 pieds, dans Saturne, et qu'elle fait un effect merveilleux.”
OC VII: 1949: 14 juni 1673 “Pour ce qui est des decouvertes que nous avons faites avec ces verres de 36 et 46 pieds;”
OC VII: 2045: 9 augustus 1675 “Celle de Campani de 36 pieds est tres bonne”

And a reference that showed me the ratio used by Huygens' of pieds to palms.

OC VII: 1856: 4 dec 1671: “Cependant Campani et Divini travaillent à qui mieux mieux a nous faire des verres de 40 pieds ou 60 palmi”

Palms differ from 22.8cm (Roman) to 25cm (Common). The IMMS information suggests palms of 11.6/52= 22.3cm i.e. approx. Roman palms (52*22.8=1185.6cm). This would when using the above relation result in a foot-unit of 33.5 cm. I will leave it at that for the moment, as it does not appear to be a fertile approach .

A reference in the Ency Britt 1911 article “Telescope”:

G. D. Cassini discovered Saturns fifth satellite (Rhea) In 1672 with a telescope of 35 ft., and the third and fourth satellites in 1684 with telescopes made by Campani of 100- and 136-ft.

I then discovered the answer in Cassini (2004, p 34):

“In fact, during a trip to the Provence in November 1672, an impatient Cassini personally went to the Marseille customs office to pick up a telescope that — with his customary skill — Campani had constructed for him; Cassini described it as “une excellente Lunette de 35 pieds” [“an excellent 35-foot telescope”](approx, 11.4m).”

The 35-foot being equal to about 11.4 meters points to Cassini using French 'feet' (35*32.48cm=1136.8cm). Huygens' 36-feet suggest Rijnlandse voeten as unit of measurement (36*31.4cm=1130.4cm). which seems in line with the fact that the letters mentioned above were written to his brothers Lodewijk and Constantijn.
From the date mentioned by Anna Cassini we can deduce that this new Campani telescope could only appear in the Versailles painting after November 1672.