S54 Professor Weber^s Description of an 



those making the port. For this reason, only the upper half 

 of the lens was used, and the lower edge of the bright flame 

 brought into focus. A very copious light is thus thrown on 

 the pier and on the water in the vicinity, so that the seamen 

 can work the landing lines, and the custom-house officer make 

 his entries with ease. The existence of the harbour light has, 

 indeed, nearly doubled the number of opportunities for enter- 

 ing the port. 



In order to complete the instrument, a reflective ring ought 

 to have been placed on the top of the annular lens, so as to 

 save some more of the rays that proceed upwards : — the funds 

 placed at my disposal did not allow of that, but I have made 

 provision, on the upper edge of the lens, for securing it there 

 if it should be thought of. 



To conclude, I may point out a mistake into which M. 

 Fresnel has fallen with regard to the reflective rings employed 

 by him. He places the focus of both the refracting and re- 

 flecting system at the lower part of the bright flame, whereas 

 the focus of the refractors only ought to be at the bottom, the 

 focus of the reflectors should be at the top of the flame. 



Edward Sang. 

 Edinburgh, l^th April 1838. 



r- 



Description of' an Experiment regard'mg the Jailing out of the 

 head of the Thigh-bone from the Socket in rarefied air, 

 explanatory of the great prostration of strength experienced 

 during the ascent (f lofty mountains.'^ By Professor Wil- 

 HELM Weber of Gottingen. 



Alexander Von Humboldt delivered an address to the Asso- 

 ciation of Naturahsts at Jena, at the public general meeting of 

 the 26th September, in which he described his ascent of Chim- 

 borazo, and compared it with the subsequent one of Boussin- 

 gault. Among other interesting subjects, he alluded particu- 

 larly to the remarkable feeling of fatigue experienced while 

 walking in very lofty regions ; and remarked that this curious 

 phenomenon may probably be explained by means of the 

 equilibration of the bones produced by the pressure of the at- 



>•"- • ' 



* Prom Poggendorflf's Annalen. 1837. No. 1, p. 8, 



