1867.] made with a Rigid Spectroscope. 11 



Date. 



Temperature 

 of prism. 



Reading. 



JJate. 



Temperature 

 of prism. 



Keading. 



1865. 



o 





1865. 



o 





Jan. 13. 



48-2 



0-67 



Feb. 12. 



52-8 



1-26 



14. 



51-5 



0-75 



18. 



52-5 



1-22 



16. 



75-6 



2-00 



23. 



49-9 



1-04 



17. 



80-8 



2-24 



24. 



50-8 



1-02 



18. 



76-0 



2-22 



March 2. 



73-7 



2-26 



19. 



74-8 



2-05 



3. 



76-8 



2-43 



20. 



75-1 



2-04 



4. 



76-6 



2-43 



21. 



70-5 



1-71 



5. 



75-0 



2-36 



22. 



75-0 



2-04 



6. 



78-3 



2-64 



2X 



74-5 



1-87 



7. 



79-0 



2-76 



24. 



75-4 



1-86 



8. 



78-9 



2-68 



25. 



74-6 



1-83 



9. 



76-8 



2-46 



26. 



75-4 



1-92 



10. 



75-5 



2-28 



27. 



77-4 



2-15 



12. 



56-3 



]-37 



28. 



75-9 



2-09 



21. 



51-0 



1-26 



29. 



76-7 



2-14 









These experimeuts consequently consist — 



(1) of a set of readings at low temperature. 



(2) „ „ high 



(3) „ „ low „ 



(4) „ „ high „ 



(5) „ „ low 



If we compare (2) with the mean of (1) and (3), and (4) with the 

 mean of (3) and (5), we obtain as the Kew correction for temperature 

 an increase of 1*44 revolution for an increase of 30° Fahr. 



On comparing the temperatures obtained under very different treat- 

 ment at the Minories at Kew, and we find — 



At the Minories 30° Fahr. gives 1*32 revolution. 

 At Kew . . .30° „ 1-44 



Mean 1-38 „ 



These two results are therefore extremely consistent with each other, 

 although the treatment to which the instrument was exposed differed 

 materially in the two cases. "We should therefore say that the tempera- 

 ture correction should not vary with change of treatment, and have 

 therefore considerable confidence in applying the above value of it to 

 observations made on board the ' Nassau.' 



II. Correction for Change of Atmospheric Pressure. 



It is justly remarked by Captain Mayne that the readings seemed to 

 vary with the barometer. 



