JURA. GEOLOGY. 205 



in the market, while on the eastern, at the same period, 

 they are full, and far inferior in quality. In comparing 

 their excellence as an article of food, these would indeed 

 be scarcely considered as the same fish. But I need 

 not dwell on a subject at present so little capable of 

 illustration: it is sufficient to have pointed it out to 

 the attention of naturalists. 



THE great regularity of the stratification of Jura cannot 

 be understood without ascending to the summits of the 

 Paps; and, to comprehend the whole as it deserves, it 

 is necessary to ascend both the northern and southern 

 mountains, since they alternately exclude the view of 

 the ground beyond each other. 5 * From Ben an oir on 



* In ascending the Paps of Jura on my last visit, the heat was 

 excessive, and, in this country, rare; the thermometer on the shore 

 standing at 82 and on the summit at 72. I may here point out the 

 utility of a thermometer much less known than it merits, although by 

 no means new ; it is the best that can be applied to the purpose 

 of observing the atmospheric temperature. In this, the bulb is no 

 larger than the stem, and the scale is applied to the tube only, being 

 a hollow cylinder of ivory. Thus the bulb is at a distance from the 

 scale, and, when taken out of its case, is free from the action of accumu- 

 lated heat. The facility with which the rays of the sun are trans- 

 mitted through glass and reflected by polished metallic surfaces, enables 

 this instrument to point out the temperature of the place in which it is, 

 although exposed to the sun's rays : it seldom rises above half a degree 

 when removed from a shady place into the open sunshine, and in par- 

 ticular positions undergoes no change, the stem forming a shade to 

 the bulb. Were it in more general use, and due precautions taken 

 against reflected and radiant heat by sheltering it from the action of the 

 ground below and other approximate bodies, we should not receive from 

 travellers such extravagant accounts of the temperature of hot climates; 

 accounts which owe their origin partly to this latter cause, and partly 

 to the heat accumulated in the scale by the sun's action. The heat in 

 the sun would in fact be seldom found to be greater than in the shade. 

 At the same time, the sensibility of this instrument is both amusing and 

 instructive ; since it is affected by every accidental breeze blowing over 

 a surface colder or warmer than the observer's station, by its vicinity to 



