324 rHILOSOPHlCAL TRANSACTIONS. [ANNOI759. 



antiquity ; and will satisfy the learned, that the Romans had penetrated into the 

 westernmost parts of Cornwall before the empire became christian : that the 

 sacrifical vessels, the paterae, and praefericulum, are of tin, the natural product 

 of Cornwall : the vase, the weights, the millstone, are also of Cornish granite : 

 and by the walls, the religious utensils, the weights, the quantity of shoes, 

 bones, horns, vases, urn, and ashes, this fort appears to have been that of a 

 fixed garrison, not a temporary occasional fortification : that by the shape of 

 this fort, and the antiquities discovered in it, it was a Roman fort. 



If. A New Improved Silk- Reel. By the Rev. Samuel Pullein, M. A. p. 21. 

 The improvements made in the reeling, and other operations relating to silk as 

 well as cotton, have been so numerous and much more important since the date 

 of this paper, that it was deemed quite unnecessary to reprint it in these 

 Abridgments. 



r. Experiments on several Pieces of Marble Stained by Mr. Robert Chambers. 

 In a Letter from Mr. E. M. Da Costa, F. R. S. p. 30. 



But before relating the experiments, it may not be improper to give some 

 little historical account of the art itself. Kircher, in his Mundus Subterraneus, 

 lib. viii, sect. 1, c. Q, p. 45 and 46, is the first author that mentions it. 

 There was, says he, an artist at Rome, who painted several pieces of marble, in 

 an elegant manner for Pope Urban VIII. He would not discover his art ; there- 

 fore Kircher strove by many experiments to discover it : and he made colours, 

 viz. tinctures of metals and minerals, which coloured the marble as finely as any 

 the artist had done, and quite penetrated the stone ; insomuch that a slab cut 

 horizontally made as many pictures as pieces or sections. Kircher gives at large 

 the process he used for making the colours ; and observes they should always be 

 of a mineral origin. The said author (Ibid.) also gives another method to colour 

 marble, by vitriol, bitumen, &c. forming a design of what you like upon paper, 

 and laying the design between 2 pieces of polished marble ; then closing all the 

 interstices with wax, you bury them for a month or 2 in a damp place. On 

 taking them up, you will find that the design you painted on the paper has pene- 

 trated the marbles, and formed exactly the same design on them. A modern 

 author, Wallerius, in his Mineralogy, vol. ii. gen. 58. p. 128. also recommends 

 this method. 



In the Phil. Trans. N° 7, Kircher's first method is copied. The editor how- 

 ever says, that method has not since been tried. He adds, that one Mr. Bird 

 had for many years (he writes in 1 666) found out a way to sink colours a con- 

 siderable depth into polished marble ; pieces of which were shown to King 

 Charles 2d, soon after his restoration ; and, being broken in his presence, it 



