276 PHILOSOPHICAL TRANSACTIONS. [aNNO J 7/8. 



surface of the ice, and the heat of the room is 62, the point of 32° should be 

 placed 7 X .OO261, or .018 of an inch lower than the observed point. This 

 correction also would be made more easy by the help of a diagonal scale, similar 

 to that proposed for the boiling point. 



On the precautions necessary to he observed in making observations with ther- 

 mometers. — In trying the heat of liquors, care should be taken that the quick- 

 silver in the tube of the thermometer be heated to the same degree as that in the 

 ball ; or, if this cannot be done conveniently, the observed heat should be cor- 

 rected on that account : but for this we refer to the former part. 



H. Cavendish ; W. Heberden ; Alex. Aubert ; J. A. De Luc ; N. JVJaskelyne; 

 S. Horsley ; J. Planta. ,. 



END OF THE SIXTY-SEVENTH VOLUME OF THE OEIGINAL. 



/. On certain Traces of f'olcanos on the Banks of the Rhine. By Sir IVm. 

 Hamiho7i, K.B., F. R.S. Vol. LXVlll. Anno \ 7TB. p. 1. 



The first certain token of volcanos having existed in this country was evident 

 to me in the court of the palace of the elector palatine at DusseldorfF, which is 

 at this moment new paving with a lava exactly like that of Etna and Vesuvius, 

 which comes from a quarry belonging to the same elector at Unkei, between 

 Bonn and Coblenz. At Cologne, I was struck with the sight of numberless 

 basaltic columns inserted in the walls of the town ; and columns of the same 

 sort are universally used as posts in the streets, and at every door ; they are 

 chiefly pentagonal, but some are hexagonal, and a few have only 4 sides ; they 

 are very like the basaltes of the Giants Causeway, but without their regular ar- 

 ticulations. These come likewise from the Unkel quarry. The walls of most 

 of the ancient buildings in the town of Cologne are of a tuffa exactly resembling 

 that of Naples and its environs. This species of stone abounds on the banks 

 of the Rhine, between Bonn and Coblenz : these circumstances made me keep 

 a sharp look out, and, on my approach to Bonn, I was struck with the volcanic 

 forms of th Sevenbergen, or Seven Mountains, about 2 leagues from the town, 

 on the other side of the Rhine. In the walls and streets of Bonn are many of 

 the abovementioned columns of basaltes, and the pavement of the town is of 

 lava. The stone in general use for building here, is a very compact one, a hard 

 volcanic tuffa like that of Pianura near Naples, and of the sort called Piperno 

 in Italy ; it is something like free-stone, but, on near inspection, is mixed with 

 fragments of lava and other volcanic substances. 



I visited Wolckenberg, Tackenfelts, and Stromberg, 3 of the Sevenbergen, 

 and found the first 2 entirely composed of tuffii. and the last of tuHii and lava : 



