DIALLING. 



693 



History, block of stone, having its base horizontal. At the bot- 

 N *^"Y"™"' torn of the cavity, a style was erected, the top of which 

 was at the centre of the sphere. It is easy to see that 

 the summit of the style would describe every day an 

 arc of a circle at the bottom, similar to the diurnal pa- 

 rallel described by the sun. The equator and tropics 

 would be easily delineated on the inside of the hemi- 

 sphere, and these being divided into twelve equal parts, 

 curve lines drawn through the divisions would be hour 

 lines, and would divide into 12 parts the trace of the 

 style, and the entire day from sunrise to sunset. Seve- 

 ral antique dials of this kind have been found ; the first 

 in 1741, in the ruins of an ancient Roman house, situ- 

 ated on Tusculum, which appears to have belonged to 

 Cicero's Cicero, so that the dial is valuable both on account of 

 *»*'• its antiquity, and its having belonged to the Roman 



orator, who seems to have referred to it in one of his 

 letters to his freedman Tiro. It was placed in the mu- 

 seum of the Roman college, and described in 1746 by 

 P. Zuzzeri, a learned Jesuit. We have given a figure of 

 it in Plate CCXXVIII. Fig. 1 ; and it may be remarked, 

 that the useless part of it has been cut off by a plane pa- 

 rallel to the equator and the tropics of the dial. This 

 plane has been found to be inclined to the earth's equator 

 at an angle of 48° 17' or 18' ; now this is precisely the in- 

 clination of thehorizon of Tusculum to the equator, which 

 shews that the dial has been made by anintelligent person. 

 A dial of the same construction was discovered in 

 1751, at Castel-Nuovo, in the ecclesiastical state, and 

 was placed by Pope Benedict XIV. in the museum of 

 the capital ; and another was disinterred the same year 

 about the same place. These exhibit ia their cavity 

 not only the hour circles, but also the equator and the 

 tropics. A third was found in the ruins of Pompeii, 

 but this differs from the others in having only the hour 

 lines and equator. 



1 3. The figures of some antique dials have been pre- 

 served on the monuments of antiquity. Gabriel Sime- 

 oni has described one which accompanied a calendar. 

 It was a triple dial, the middle one traced on a concave 

 cylindric surface, and the two lateral ones on plane sur- 

 faces. There was formerly a dial at Ravenna, which 

 had the figure of a hemisphere supported on the shoul- 

 ders of a Hercules : it was turned towards the south. 

 Lambecius has also preserved the figure of a dial sup- 

 ported on a column. Pie copied it from a very ancient 

 manuscript in the imperial library. It wants the upper 

 part of the hemisphere, which would have been useless, 

 because the shadow of the extremity of the stile pass- 

 es only over the inferior part. 



14. A very curious portable dial was dug out of the 

 ruins of Portici in 1755, and described in the preface to 

 the third volume of the description of representations 

 found in the ruins. Its shape is that of a bacon ham ; 

 and it is suspended to a ring fastened to the leg. The 

 end of the tail, which has been preserved, serves as a 

 stile. Its figure is shewn in Plate CCXXVIII. Fig. 2. 

 The hours are marked on that part of the surface which is 

 nearly plane. There appears to be seven vertical lines 

 intersected by as many others, and below these inter- 

 vals the names of the months are written. Such as un- 

 derstand dialling will readily see how this dial is to be 

 used. It must be suspended by the ring, and turned 

 slowly round, until the shadow of the top of the stile 

 fall upon the line of the month, the hour will then be 

 indicated by the nearest transversal line. 



1 5. The theory of sun dials must have been cultiva- 

 ted among the Arabians along with the sciences of ma- 



thematics and astronomy, upon wliich it depends, du- 

 ring the period when Europe was enveloped in the 

 darkness of ignorance ; and some manuscript treatises 

 of their astronomers on this subject are to be found in 

 the repositories of literature. In the Bodleian library, 

 there is a treatise on sun dials by Takioddin Ibn Marysh, 

 who lived about the year 1579; and it contains 

 others by Abul-Hazen de Maroc and Mohalled. Then- 

 celebrated philosopher Jacob Alkendi, has also written 

 on shadows ; and it was probably a treatise of his on 

 sun dials that was called Sciolherica. 



The necessity of a method of dividing time, has in- 

 duced even the Turks to attend to this subject. One 

 of their astronomers, Mustapha ben Ali, who lived about 

 1533, has written a treatise on sun dials, and the divi- 

 sion of time. 



16. Upon the revival of learning in Europe, the sci- 

 ence of gnomonics was again cultivated, and treatises 

 were composed on the subject by John Stabius, Andrew 

 Stiberius, and John Werner, astronomers of the 15th. 

 century ; but they have remained in manuscript. To 

 these may be added John Schoner, an astronomer of the 

 beginning of the 16th century, who published in 1515' 

 a work called H ovarii eglindri canones, where he 

 teaches the construction of c)dindrical dials. Plis other 

 gnomonical works were afterwards published by his 

 son. Other early writers on this subject, were Mun- 

 ster and Orontius Fineus. The first of these pub- 

 lished at Basil in 1.531, a work called Compositio 

 horologiorum in piano muro, &c. and the latter brought 

 out in 1532, Ins work de Horologiis solaribus et qua- 

 drantibus, libri iv. Among the gnomonists of that age 

 may be rekoned Vinet and Bullant, who have written 

 in French. The Chartreuse John Bat. Vico Mercati, 

 who lightened his solitude by writing his treatise De- 

 gli horologi solari. Commandinus, whose work is call- 

 ed de Horologiorum description, and who afterwards 

 published an edition of the Analemma ofPtolemy. Mau- 

 rolycus, whose treatise de Lineis korariis appeared in 

 1575. Paduanus of Verona de compositione et usu mul- 

 tiformium horologiorum. Valentino Pini, J. B. Beneditti 

 or de Benedictis, who published a treatise de Gnomo- 

 num umbrarumque solarium usu 1574; and Clavius the 

 Jesuit, whose Gnomonices, libri viii. appeared in 1581 and 

 1599. 



17- The Portuguese astronomer Nonius, deserves 

 to be mentioned here, on account of his having noticed 

 and explained the phenomenon of the retrogradation of 

 the shadow on a dial in certain latitudes. Some have 

 supposed that it was in this way the shadow went back 

 on the sun dial of Ahaz, but this explanation seems 

 quite inadmissible. 



18. The 17th century produced a multitude of works 

 on dialling in all languages, and suited to all capa- 

 cities, from the geometer, who required merely the the- 

 ory in order to see at once all its applications, to the 

 stone mason, who, ignorant of its principles, could only 

 follow practical rules. The principal writers of this 

 age were Muzio Oddi Degli Orologi Solari (Mil. $• 

 Ven. 161 1 and 1638, in 4to.) ; Kircher, Ars magna lucis 

 et umbra; ; P. Maignan, Perspcctiva horaria, lib. iv. 

 (Rome 1646 in fol.) ; Deschales in his Cursus Math. 

 (Ludg. 1674 and 16.90, in fol.) ; Forster, The art of di- 

 alling, &c. (Lond. 1638, in 8vo. ) ; Collins' Description 

 and use of a great wiiversal quadrant, (Lond. 1658); 

 Desargues, La meihode de Gnomonique, (Paris 1641, in 

 4to.) ; De la Hire, Gnomonique, (Paris 1681, in 8vo.); 

 Ozanarn, Gnomonique, (Paris 1673, in 8vo.) ; WebV 



History. 



