The Mars Sketch here by DOLLFUS was made on 17 April 1997 22:00 TU (106 degs Ls). Used 233x10cm Astroscope (Fig 3). The planet was going away and the apparent diameter was 12.7 arcsecs. The phase angle was 23.5 degrees, and DOLLFUS detected a defect of illumination. The LCM was 025 degs W, and M Acidalium was evident. The other dark marking at upper left must includes Aurora S. The season was 106 degs Ls, and hence the area of the north polar cap (2"x1" in angle) did not well show up, just light obscure.
Professor DOLLFUS also made a sketch of Mars by 100x10cm, and interestingly compares it with a drawing of Ganymede (of 1.2" arcsecs) anotherly made by the use of 1000x100cm at the Pic du Midi. Apart from the contrast, the images are quite similar.
The drawing by DOLLFUS reminds us of a sketch by Ch HUYGENS made in 1683 (Fig 4). HUYGENS obtained the drawing cited here on 7 April 1683 at 9.5h by the use of a 36 pieds refractor. The refractor used by him was not any astroscope without tube, because the idea of the latter was introduced after August 1683. Although F TERBY made a different interpretation, we may say that HUYGENS also saw M Acidalium if we compare both drawings.
As detailed in CMO #106 p909 by the present writer, the year difference 284 is one of the best recurrence year to produce a similar Mars season as well as the apparent diameter (that is, both planets meet at the similar points on their orbits). Since 1683+284=1967, HUYGENS' Mars was similar to the planet in 1967. In 1967, Mars was at opposition on 15 April with the season 120 degs Ls, and so the north polar cap must have been smaller than that in the case of DOLLFUS. This implies in turn that it was hard for HUYGENS to detect the npc also. (We add that the 1999 Mars is in another sense a returned planet of the 1683 Mars since 4x79+1683=1999, where 79 is another -not best- recurrence year.)
It is described by DOLLFUS that it was because the diameter of the south polar cap was of the dimension of 6 arcsecs that HUYGENS did discover the polar cap on 13 August 1672. Yes, 1672+284=1956, and the 1956 Mars showed us the south polar cap clearly as well as the great dust storm. At another page, Professor DOLLFUS compares his detailed drawing of Mars in 1956 with the famous one by HUYGENS made in 1659 (made on 28 Nov 1659) both of which describe Syrtis Major and alludes to the decisive progress made during the 300 years. Prof. DOLLFUS is right, but one thing to be noticed is that there is a natural reason why HUYGENS did not write the polar cap in 1659, and in this point HUYGENS' 1659 drawing should not be compared with any drawing in 1956. The reason is simple:1659+284=1943 and hence HUYGENS' Mars corresponds to the 1943 Mars if we refer to the planet at hand. Mars was closest to the Earth on 29 Nov 1943! when the season was 345 degs Ls and De=5 degs S, and therefore we can say in 1659 nobody could have detected the south polar cap.
N.B.: We should incidentally note that at p 444 of the April 1992 issue of the Sky & Telescope, Alan BINDER wrote about his experience on an application of his 7.5 cm Hevelius-type telescope to the planet Mars in 1988. The south polar cap was detected as well as some dark markings by the 5.2-metre-long Hevelius. (Hevelius himself used a 45-metre-long telescope.)