234 



SIE DAVID BREWSTER 



Angles of Incidence i. 



Angles of Refraction t. 



Botation R. 



Length of Tangent. 



64° 40' 



36° 46' 



7 



2-386 inches, 



67 29 



37 43 



8 



2-726 



70 



38 29 



9 



3104 



72 19 



^ 39 7 



10 



3-544 



. By setting off the tangent 0-655 inch from the zero at F, we obtain the place 

 of 1° of rotation, and so on with the rest. The polariscope P is then placed at 

 the end FH of the tube. 



Having observed the maximum polarisation of the atmosphere by the polari- 

 meter, and its place, we take its altitude A, and by means of the sun's altitude A', 

 observed or computed, we obtain the distance D of the place of maximum polari- 

 sation from the sun : — 



D = 180° - A + A'. 



The following are all the values of D which I obtained. I have added the 

 values of R or the degrees of polarisation in the zenith and in the horizon, when 

 they happen to have been measured : — 



Observations in 1841. 





Apparent Time. 



Values of D. 



Rotation in 

 Zenith. 



Rotation in 

 HorizoD. 



April 



28. 



S^ 



Qm 





88° 



16' 



• • • 



• • • 



5) 



30. 



2 



5 





79 



15 



... 



* *• 



May 



17. 



1 



20 





99 





18^° 



151° 



June 



6. 



4 



45 





+ 90 





161 



221 



>) 



9. 



4 



30 





+ 90 





25^ 



24^ 



J5 



10. 



10 



39 





92 



35 







95 



10. 



12 









88 



26 



30 15' 



29 



Sept. 



15. 



10 



18 





88 



4 



27 



261 



Oct. 



26. 



4 



30 





93 





28J^ 



27^ 



Dec. 



17. 



9 



7 



A.M. 



Appt. +90 





27 



24^ 



}} 



18. 



9 







9> 



time. + 90 





28 



27 













Observations in 1842. 











Apparent Time. 



Values of D. 



Rotation in 

 Zenith. 



Rotation in 

 Horizon. 



Jan. 



7. 



9^ 



Om A.M. 



120° 





Haze 



241° 



April 



5. 



6 



58 





+ 90 





3or 



261 



)» 



20. 



12 



49 





84 





25 



17 



)> 



j> 



2 



25 





86 





25 



19 



)» 



)> 



3 



35 





88 



20' 



25 



• • . 



» 



55 



4 



32 





90 





27 



17 



9> 



21. 



11 









90 





23 



* • • 



JJ 



5) 



12 









90 





23 





>> 



59 



1 



10 





90 







25 



J5 



25. 



1 



17 





90 





26i 





»J 



26. 



10 



63 



A.M. 



90 





29 



• ■ • 



5> 



?> 



11 



46 





88 





29 





>) 



?3 



3 



42 





88 





29 



■ > ■ 



3) 



27. 



10 



41 



A.M. 



87 





29 



• . • 



J J 



28. 



11 



34 



A.M. 



87 





29 



■ • • 



») 



28. 



1 



50 



55 



88 





29 



• • • 



)J 



29. 



1 



34 



55 



87^ 





29 



... 



May 



3. 



11 



29 



55 



89 





20 



• c. 



