106 Fisher on the Variation of the Compass. 



comparing the sun's noon and midnight meridional zenith 

 distances*. 



The aurora boreahs was seen on our returning to England, 

 exceedingly vivid, but no sensible effect was produced on the 

 compasses. 



Art. IX. Observations on the Theory which ascribes Secre- 

 tion to the Agency of Nerves. By W. P. Alison, M.D. 

 F.R.S.E., 8fc. Professor of Medical Jurisprudence and 

 Medical Police in the University of Edinburgh. 



[Communicated by the Author.] 



The importance of Dr. Wilson Philip's Experimental Inquiry 

 into the Laws of the Vital Functions must be obvious to all who 

 study, with the attention it deserves, his refutation of the theory 

 of Le Gallois, concerning the connexion of the nervous system, 

 in the living body, with muscular action, contained in a work 

 which the French National Institute characterized as " certainly 

 the most important which has appeared in physiology since the 

 learned experiments of Haller," and the doctrines of which 

 that learned body, somewhat hastily, sanctioned and adopted. 



The most prevalent opinion in the schools of medicine, in re- 

 gard to the connexion of the nervous system with muscular ac- 

 tion, has been, that the muscles derive from the nerves, not 

 merely occasions of irritation, but supplies of irritability, in the 



* The apparent meridional zenith distances of O centre at noon and 

 midnight, observed by Lieutenant Morell and myself, were, at noou, 

 69°.38.'6", and midnight 79°.10'.57",4. 



— . O t n 



If A=obs. Z.D. O centre atnoon corrected for Parallax . . =59.38.6' 



a = do at midnight =79.10.57,4 



rf = Q declin. corresponding to A corrected for long... =20.35.1 



rf'= Ditto a =20.29.10 



r = refraction of the tables corresponding to A = 0. 1.37" 



»•'= ditto a = 0. 4.51 



X = True refraction corresponding to A 



3/= ditto a 



Then since x+x'=lSO°—{A + a + d+d')= m 



and X : 3/ :: Tang. (A-3r) : Tang. (a—Sr') 

 m. Tan. (A— S r) 

 •• =*' Tan. (A-3r)+Tan.ra-3r'} "" l'-39"- 



w.Tan. {a-3?) ^ ^^ 



^~ Tan (A-3r)+Tau.(«-3r') "" ^'•^'^ '' 

 nearly the same as the refraction iu the tables, at the mean temperature 

 and pressure. 



