222 PHILOSOPHICAL TRANSACTIONS. [aNNO 1771. 



very speciously produced in favour of his own observation at the island of 

 Rodrigues, as represented in his learned memoir on the sun's parallax, will pro- 

 bably be of opinion, that an error of one minute was committed in writing 

 down the time of hi observation, as was conjectured by many persons, as well 

 as myself; a mistake to which the most experienced observer is sometimes 

 liable, when at the time of observation the minute is nearly completed. 



The parallax on the 3d of June being 8".65, the mean parallax will be found 

 to be = 8".78; and if the semidiameter of the earth be supposed = 3985 

 English miles, the mean distance of the earth from the sun will be 93,726,900 

 English miles. And, as the relative distances of the planets are well known, 

 their absolute distances, and consequently the dimensions of the solar system, 

 will be as follows : 



Relative distance. Absolute distance. 



Mercury 387,10 36,281,700 



Venus 723,33 67,795,500 



Earth 1000,00 . . 93,726,900 



Mars 1523,69 142,818,000 



Jupiter 5200,98 487,472,000 



Saturn 9540,07 894,162,000 



LIV, A short Account of some Basalt Hills, in Hessia. By Air. R. E. Raspe, 



F. R. S. p. 580. 



Mr. R. discovered in the neighbourhood of Cassel, several hills, composed of 

 basalt rocks, formed in polyedrous and mostly pentagonal columns. As this sort 

 of stone has hitherto met with few observers, and affords many curious singu- 

 larities, Mr. R. gives the following account of his researches. He observes 

 that the German basalt rocks differ from those of the giant's causeway in 

 Ireland, by their want of articulation ; and from those anciently found at Syena 

 in Egypt, and described with tolerable exactness by Strabo, lib. 17, by their 

 being less thick, and not exceeding 8 or 10 inches in breadth, on unequal 

 lengths from 5 to 30 feet. The colour, hardness, weight, and substance of 

 these stones sufficiently show them not to belong to the genus of the marbles, 

 among which Mr. Da Costa ranked them, in imitation of the ancients. 



Their substance is vitreous, analogous to that of the horny stones; they resist 

 aqua fortis, and the chizzel: and only yield to a violent fire and the engravers 

 wheel. Being worked in this manner they acquire the polish of the ancient 

 basaltes, named by the Italians Marmo paragone. Mr. R. had not completed a 

 chemical analysis of these stones, which he says they richly deserve, chiefly as 

 they contain small nests of crystals of tin ore, yellow, green, and black. These 



* See Phil. Trans., vol. 53, for the year 1763. p. 491. 



