December 5, 1901] 



NA TURE 



105 



enclosure, on which portable instruments could be used 

 when necessary. 



In the centre of each crypt was a large instrument, 

 the floor rising gradually by circular stone steps (shown 

 on the plan) up to the walls. The floor of the crypt G 

 was, however, flat ; in it was placed a sextant of 5^ feet 

 radius for measuring angular distances in any plane. In 

 the southern crypt (c) there was a large equatorial 

 instrument, consisting of a declination circle of gi feet 

 diameter, revolving round a diameter parallel to the 

 earth's axis, and having a semicircle of 12 feet diameter, 

 supported on stone piers and representing the northern 

 half of the equator. In the crypt F stood a quadrant of 

 7 feet radius, enclosed in a square and with an azimuth 

 circle on the wall, in n another quadrant somewhat 

 smaller and in E a zodiacal armilla like those used by 

 the ancients. Of these instruments those in c and F 

 were the most important, and an immense deal of 

 valuable work was done with them. 



Of this observatory and of the instruments in it very 

 full and well-illustrated descriptions were published by 



=.— Plan of Stjerneborg :— a, entrance ; b, sludy ; c, crypt with lareest 

 armilte; p crypt with qu.ulr.-int: e, crypt with zodiacal armilla:; 

 F, crypt with largest quadrant : G, crypt with sextant ; H, i, stone piers 

 for portable armilla ; K, L, n, t stands for se.«ants ; m, stone table ; 

 o, Tychos bed; p, stove; v. table: o, bedroom for assistants; 

 s, unlinished underground passage towards Uraniborg. 



Tycho. When he left Denmark he took all his instru- 

 ments with him except the four largest, two of which 

 were those in the crypts C and F, and the large equa- 

 torial was actually used by an assistant to observe the 

 partial eclipse of the sun of February 25 (March 7), 1 598.' 

 They were, however, subsequently dismounted and sent 

 to Bohemia, where every single instrument from Hveen 

 was destroyed during the thirty years' war, except Tycho's 

 large star-globe, which found its way back to Denmark 

 only to perish in a great fire in 1728. 



When Ekdahl, as already mentioned, examined the 

 site of .Stjerneborg in 1823-24, he found without difficulty 1 

 the floors of the central study and of all the crypts more i 

 or less well preserved, one of them (f) being almost ' 

 perfect, with the four circular steps and the short stone 



1 See Monthly Notices R.A.S., vol. liv. p. .^a. ' 



NO. 1675, VOL. 65] 



pillar in the middle on which the quadrant had been fixed. 

 In the course of years everything became again covered 

 with earth and grass except the crypt F, which was 

 always visible, though generally more or less full of 

 water. It furnished a valuable clue to the unit of linear 

 measure employed by Tycho, as d'Arrest, in 1868, found 

 the diameter of the crypt to be 11 \ Paris feet, which must 

 be equal to the diameter of the azimuth circle of the 

 quadrant which Tycho states to have been nine cubits. 

 This gives one cubit = i6'i English inches = 40-9 centi- 

 metres. Tycho, however, also makes use of feet, and 

 d'.'^rrest found to his surprise, on measuring the length 

 of the ramparts round Uraniborg, that the whole place 

 was much smaller than the figures given by Tycho had 

 led him to expect, the enclosure being only 233 French 

 feet square instead of 300. The discrepancy was, how- 

 ever, easily cleared up, as Picard had carefully measured 

 the great star globe in 1671, which gave one Tychonic 

 foot = o'8i5 English = 24^9 centimetres. These figures 

 are of importance, as it is of interest to know the exact 

 dimensions of the instruments, by means of which so 

 great a revolution in practical astronomy was carried 

 out. For instance, the radius of the great quadrant (in 

 f) was five cubits long ; one minute of arc was, there- 

 fore, o'6 millimetre in length, and as Tycho says that he 

 could by his transversal divisions distinguish 10", this 

 means that he could read off the arc to a tenth of a 

 millimetre. In reality the accuracy attained was hardly 

 as great, the probable error of one measure of altitude 

 being certainly more than half a minute. But even this 

 was a wonderful advance on what had been possible 

 before Tycho's time, when errors of three or four minutes 

 were unavoidable. 



During the past year the site of the observatory has 

 again been thoroughly excavated under the super- 

 vision of the Swedish inspector of antiquities and 

 Prof Charlier, of Lund. From the account published 

 by the latter it appears that the tiled floor of 

 the central study is almost perfectly preserved ; it 

 is 4 metres long (from north to south) by 3^ metres 

 broad. The floor of the alcove where Tycho's bed stood 

 is also visible, the dimensions being only 185 by 125 cm. 

 As it seems to have been completely underground, this 

 tiny and grave-like bedroom can hardly have been a 

 healthy place of rest, and it is to be hoped that the 

 energetic observer did not use it very often. The floor 

 of the study was found to be two metres below the 

 ground. As Prof. Charlier's account is in Swedish, it 

 may not be useless to give here a summary of the re- 

 sults of his examination of the five crypts. Of D, G and 

 C the floors are left, all on the same level as the floor of 

 B, and in D also the short pillar to which the lower end of 

 the vertical axis of the quadrant was attached. The 

 polished stone floor of E was 125 cm. above that of the 

 study li and the steps leading up to it from the little 

 vestibtile north of the study are still intact. But the 

 crypt F is almost in perfect preservation, with its four 

 steps, the floor being 122 cm. below that of the study (or 

 10 feet below the ground), the innerdiameter of the lowest 

 step being 88 cm. and the outer diameter of the top step 

 345 cm. The top step was exactly on a level with the 

 floor of the study. As the diameter of the top step was 

 of importance for fixing the length of Tycho's cubit, it 

 was measured again by a second observer, who found 

 354 cm. The mean of the two measures gives i cubit = 

 3S'8 cm., agreeing sufficiently well with the 40^9 found by 

 d'Arrest. Prof Charlier found the value of a Tychonic 

 foot from measures of the length of the foundation-wait 

 of Uraniborg equal to 238 cm. ; but as Tycho only says 

 that the side of the square was "circiter pedes 60," this 

 result can hardly be as accurate as that deduced from 

 Picard's measure of the star-globe, as it seems likely that 

 the latter was exactly 6 Tychonic feet in diameter, which 

 Picard found equal to 55^^ French inches. 



