174< Dr. Winn 07i a remarkable Property/ of 



which gives 



From this result we learn, 1st, that since « is the same for 

 all values of ^, every molecule vibrates to and fro in a straight 



line; 2nd, that « varies as — ^ , that is, directly as the thick- 

 ness of the crystal through which the ray has passed, and in- 

 versely as the square of the length of the wave. 



These results are equivalent to the well-known experi- 

 mental laws of Blot; hence we conclude that our formulfe 

 (23.), (25.), (26.), (27.), represent correctly the motions which 

 constitute a ray of light passing through the crystal in the 

 direction of its axis. 



On looking at the length of this paper I think it will be 

 best to reserve the remainder of the investigation for another. 

 I am, Gentlemen, yours, &c. 



Littlemoor, Clitheroe, Jan. 9, 1839. JoHN ToVEY. 



P.S. In the paper, vol. xii. p. 11, line 8, Jbr <f> (r) read 

 <P{r)Ayj; ibid. Vine 9, Jbr ij' (r) read <^(r)A^; and p. 12, 

 equations [1.) for p^^a^i {n^^t—k x—b), read Pna^^ sin {n^^t 

 —kx — b). The corrections of a few other errors in the same 

 paper have been previously given. 



XXX. Oil a remarkable Property of Arteries considered as 

 a Cause of Animal Heat. By J. M. Winn, M.D.* 



A BOUT three years since whilst making a few experiments 

 -^^ with caoutchouc, I was forcibly struck with the property 

 it possesses of evolving heat when suddenly stretched, and 

 was led at the time to infer the probability of other bodies 

 being similarly endowed. The elastic coat of arteries espe- 

 cially, from the mechanical resemblance it bears to caout- 

 chouc, appeared to be one of the substances most likely to 

 exhibit this calefactory principle ; and in the event of this be- 

 ing the case it would not be unreasonable to conclude that 

 the incessant contractions and dilatations of the arteries du- 

 ring life must prove an efficient source of animal heat. 



During the past week I was induced to resume the subject 

 afresh, and upon making an experiment with part of the 

 aorta of a bullock, I felt much gratification in being able 

 to verify my previous conjecture. The experiment was per- 



* Communicated by the Author. 



