Prof. Draper on the AUotropism of Chlorine. 327 



for determining the motion the approximate equations follow- 

 ing: 



dx " dt^ dy dt^ dz ~~ dt' 



Hence, supposing no force impressed, we obtain approxi- 

 mately, 



Tt\dlf~di)~' TATz" d^J ~ ' 



d . /dv (i'^\ _ () 



di\dz dy) 



These equations are true, not because the functions in brackets 



, -.11 -1 du dv du 



do not contam t, but because approximately -j- = -r-, -r- 



ay O/X CL % 



diso dv d lio 

 = -j—f and -r^ = -j-. Thus the corresponding equations 



above are accounted for without affecting the generality of the 

 previous reasoning. 

 Cambridge Observatory, Sept. 29, 1845. 



L. On the AUotropism of Chlorine as connected isoith the 

 Theory of Substitutio?is. By John William Draper, 

 M.D., Professor of Chemistty in the University of New 

 York*'. 



[With a Plate.] 



T^HE researches of M. Dumas on chemical types have 

 -*- shown that between chlorine and hydrogen remarkable 

 relations exist, indicating that the electrical characters of ele- 

 mentary atoms are not essential, but rather incidental proper- 

 ties. 



The extension of these researches has given much weight 

 to the opinion that the electro-chemical theory may be re- 

 garded as failing to account for the replacement of such a body 

 as hydrogen, by chlorine, bromine, oxygen, &c. 



I do not know that as yet any direct evidence has been of- 

 fered that the electrical character of an atom is not an essen- 

 tial quality, but one that changes with circumstances. It ap- 

 pears to be ratiier a matter of inference than of absolute de- 

 monstration. 



It is the object of this memoir to furnish such direct evi- 

 dence, and to show that chlorine, the substance which has 

 given rise to the discussions connected with the theory of sub- 

 stitutions, under the very circumstances contemplated, has its 

 electro-chemical relations changed. 



* Communicated by the Author. 



