On the Calculation of the Orbits of Double Stars. 279 



crucible set in a common fire, assisted with the bellows. 

 The register A was prepared with the iron bar and held down 

 in the metal, which was supplied from time to time so as to 

 insure its very gradual fusion, and some portion always re- 

 maining in the solid state. In ten minutes time it was re- 

 moved, and when cold the arc measured was 2° 45', equivalent 

 to an expansion of '0239. 



A dry stick of deal plunged into the melted metal for a few 

 seconds caused a violent ebullition, and was deeply charred. 

 The zinc in this state did not appear red in the light. 



Exp. 18. About 12lbs. of zinc were melted in a smaller 

 crucible : the register B prepared with the iron bar was im- 

 mersed in it ; but instead of being gradually supplied, the heat 

 was allowed to increase after fusion till it began to burn : at 

 this point there was an evident blush of red upon its surface. 

 The arc measured upon this occasion was 4-° 7' = expansion 

 •0358. 



[To be continued.] 



XXXVI. On the Calculation of the Orbits of Double Stars. 

 By Professor Encke. 



[Continued from vol. ix. page 410.] 



T N making the corrections for the purpose of fulfilling the 

 -■■ equations of condition, one may be guided by the conside- 



dp 



~dt 



If, therefore, several p have been observed at intervals of time 

 not too great, but likewise not too small, so that we may put, 



approximately, — y- in place of -rj- ; and if the distances ap- 

 pear to be more certain at one epoch than at another, one 

 may correct the distances at the other epoch, having 



"We have already observed, that the angles of position appear 

 to be capable of a more accurate determination than the di- 

 stances. On account of the uncertainty of the observations of 

 the angles of position, it will not be advisable to take A t too 

 small. As soon as one is pretty near the truth, and a rough 

 drawing will, in most cases, lead us so far, these trials appear 

 to be most ade(juate to the purpose on account of the simple 

 form of the equation. In the beginning it will, however, be 



necessary 



ration that h =s f ^4- = constant. 



