Remwks on the Trilohite. 25 



is sufficient to account for the 27 feet on ground so unequal as 



a 



Bo 



a difference, that it rather proves the exactness of my calculation- 

 In Popayan we have 99 feet ; yet the difforent barometrical meas- 

 urements of that city differ still more widely, CaJdas observes, 

 p. 31, " The Baron de Humboldt's barometer stood in Popayan 

 at 23 3.4, mine at 22 11.2, and Bouguer's at 2210.7." The 

 most accurate measurements of the peak of Teneriffe, selecting 

 4 out of 14, leaves a difference of 71 French toises, or rejecting 

 the barometric measurements of Borda, of 18 toises. — Humboldt^ 

 Pers. NaT. v. 1, p. 160, 170. Saussure is said to have found 

 water boil at 187*^ on the summit of Mont Blanc, being, accord- 

 ing to Humboldt, 15,660 ft. It is 90 ft. only below the point on 

 Pichincha, where 1 found it to boil at 186^. The elevations 

 nearly equal the difference cannot amount to a degree ; and I 

 consider the error less likely to be on my side, because I was 

 aware of the probable cause of error, and had to deduce the 

 height from the accuracy of the observation, Humboldt in the 

 sarjie manner suspects the accuracy of Laraouroux's observation 

 on the peak of Teneriffe. — P. Nar. vol. i. p. 1 



[To be continued.] 



Art. II.^ — Remarks on the Trilobite ; by Jacob Grekn, M. D., 

 Professor of Chemistry in the Jefferson Medical Collegej Phila- 

 delphia. 



Remarks. — We are informed by the author that the present 

 communication was written originally for this Journal ; but some 

 peculiar circumstances induced him to publish it (March 16, 1839) 



r 



in the Friend, a weekly Journal of Philadelphia, By the author's 

 request it is now republished with additions, — Eds. 



The anatomical structure and physiological history of the 

 whole family of the trilobites are not only involved in great ob- 

 scurity, but we can scarcely hope that the most persevering 

 efforts of the naturalist will ever be able to penetrate the darkness, 

 or unravel the mysteries, which involve the subject. No depart- 

 ment in the science of organic remains has been pursued of late 

 with more zeal and curiosity than this. The trilobite furnishes 



V<i. xxsvii. No. 1.— July, 1839; bis. 4 



