287 



KDomledge & Seientifle Nems 



A MONTHLY JOURNAL OF SCIENCE. 



Conducted by MAJOR B. BADEN-POWELL, F.R.A.S., and E. S. GREW, M.A. 



Vol. II. No. 13. 



[new series.] 



DECEMBER, 1905. 



SIXPENCE NET. 



CONTENTS.— See Page VII. 



TKe Greact Gnomon 

 a^t Florence. 



By W. Alfrud Parr. 



Of the crowds of worshippers who, on Midsummer 

 Day, yearly assemble beneath the vast dome of the 

 Cathedral at Florence to commemorate the festival 

 of San Giovanni, the patron-saint of their city, but 



Fig. I.— The Cathedral (Sta. Maria del Fiore) at Floreoee, from the 

 south ; showing the window in the lantern to which the Qnomon 

 is attached. 



few probably give a thoutjht to the astronomical signi- 

 ficance of the day they are celebrating. Yet Brunel- 

 leschi's wonderful dome — over 138 feet in diameter, 

 and, with its lantern, 387 feet high* — which marked an 

 epoch in architecture, and was the first great triumph 

 of the Renaissance, forms, with its famous gnomon, 

 placed there by the Florentine cosmographer Paolo 

 Toscaneili about the middle of the 15th century, un- 

 doubtedly the most stupendous astronomical instru- 

 ment for determining the summer solstice that the 



* The corresponding dimensions of the dome of St. Paul's are 

 112 feet and 364 feet respectively. 



world possesses. So, at least, thought the great 

 Lalande in 1765, when he wrote : " La meridienne que 

 Ton voit dans la Cathedrale de Florence est le plus 

 grand monument d'Astronomie qu'il y ait au monde. " 

 But that was some 30 years before his countrymen 

 gave to the world, as an earnest of the eventful ex- 

 pedition culminating in the Battle of the Pyramids, 

 that memorable work, the " Description de I'Egypte," 

 which has formed the starting-point for our pre- 

 sent day knowledge of the design and orientation 

 of many O'f the great temples on the banks of the Nile. 

 Compared with some of these, the Florence " Duomo," 

 considered as a solstitial instrument, must take a very 

 subordinate position in regard tO' the length of the beam 

 of light utilised. 



The temple of Amen-Ra, at Karnak, for instance, 

 was, according to Sir Norman Lockyer, oriented tO' the 

 summer solstice in such a way that the setting sun 

 flashed a beam of light along its huge axis, something 

 like 500 yards in length, into the sanctuary at the ex- 

 treme end, heralding to the priests the commencement 

 of a new solar year, and affording them, at the same 

 time, an obvious means of impressing the multitude 

 with a " Manifestation of Ra." -A^t Florence, it is 

 true, Toscanelli's solar apparatus plays no part in the 

 structural scheme of the grand cathedral in which it is 

 placed, although the idea of utilising the ample propor- 

 tions of a vast public edifice in the interests of astro- 

 nomy is the same. At Florence, moreover, " the sun 

 had from the South to bring solstitial summer's heat,'' 

 and thus mark his greatest northern declination from 

 the equator instead of being required, as in the sun- 

 god's temple, to register his greatest northern ampli- 

 tude along the western horizon. The method here 

 adopted is, indeed, the venerable one of the gnomon ; 

 and, having regard to the fact that the Florentine con- 

 trivance is higher than the similar apparatus in the 

 churches of S. Petronio, at Bologna (which, by the way, 

 was constructed in 1653 by the first Cassini, the dis- 

 coverer of the chief division in Saturn's Ring), S. Maria 

 degli Angeli, at Rome, and St. Sulpice, at Paris, put 

 together, Lalande 's claim for it may not be so far from 

 the truth as regards this particular form of solstitial 

 instrument. 



Situated at a height of nearly 300 feet above the 

 floor of the Cathedral, and firmly built into the marble 

 sill of the southern window in the lantern surmounting 

 the dome, Paolo Toscanelli's famous gnomon must cer- 

 tainly have constituted, together with its solstitial 

 marble let into the pavement far beneath, a very effi- 

 cient instrument of precision in the days that preceded 



