62 Lartet on the Asphalt of the Dead Sea. 



the position of the flat mirror makes this stop work excellently 

 with the podura scale. Thus this arrangement enables an 

 experimenter viewing a new object to see surface markings, 

 and to obtain penetration with one and the same stop, an 

 important gain in original investigation. For lined objects, 

 other combinations will do better, but it is remarkable how 

 well distance lines can be shown with only 40° aperture of the 

 condenser, and no central stop at all. The slot stops have 

 been found very useful in investigating unknown objects, as 

 well as in displaying those that are known ; and with the whole 

 aperture and the two-slot stop many diatoms with double sets 

 of lines are brought out very powerfully. The microscopist 

 will find that from 40° to 59° angle of aperture will, in many 

 cases, give the best results, when a one-fourth or a one-fifth 

 objective is employed, though a larger aperture would be 

 desirable to display the same objects if another condenser 

 made of smaller glasses should be used. 



LABTET ON THE ASPHALT OF THE DEAD SEA. 



The following paper of M. Louis Lartet will be found in 

 Oomptes Rendus, No. 26, 1866 : — 



" The ancient traditions concerning the appearance of 

 bitumen on the surface of the Dead Sea bear testimony to the 

 evident connection of this phenomenon with the persistent 

 activity of the internal forces of the globe in this region, and 

 which have given rise to profound dislocations of cretaceous 

 and nummulitic rocks, to the flow of volcanic matter, and to 

 thermal springs. In our own times, some travellers who, like 

 the American missionary, Smith, had the advantage of know- 

 ing the Arabic language, have been able to obtain, from tribes 

 actually stationed in this region, tolerably consistent accounts 

 of the more recent appearances of bitumen in the waters of the 

 Dead Sea. It seems that the appearance of this substance is 

 always preceded by subterranean commotions. Thus, after 

 the earthquake of 1834, a considerable mass of bitumen made 

 its appearance at the southern end of the sea, and the Arabs 

 detached about 220 quintals, out of which they made a good 

 profit. 



" In 1820, when another earthquake destroyed a great part 

 of the city of Tiberias, and occasioned the death of more than 

 6000 inhabitants of the district, very violent shocks occurred 

 in the direction of the great axis of dislocation of the basin ; 

 new hot springs uprose in the Tiberiad ; and a few days after- 



